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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code> --- 正则表达式操作</a><ul>
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<section id="module-re">
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<span id="re-regular-expression-operations"></span><h1><a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> --- 正则表达式操作<a class="headerlink" href="#module-re" title="永久链接至标题">¶</a></h1>
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<p><strong>源代码:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/re.py">Lib/re.py</a></p>
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<hr class="docutils" />
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<p>本模块提供了与 Perl 语言类似的正则表达式匹配操作。</p>
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<p>模式和被搜索的字符串既可以是 Unicode 字符串 (<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>) ，也可以是8位字节串 (<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>)。 但是，Unicode 字符串与 8 位字节串不能混用：也就是说，不能用字节串模式匹配 Unicode 字符串，反之亦然；同理，替换操作时，替换字符串的类型也必须与所用的模式和搜索字符串的类型一致。</p>
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<p>正则表达式使用反斜杠字符 (<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) 来表示特殊形式或允许使用特殊字符而不表达其特殊含义。 这与 Python 为相同目的在字符串字面量中使用相同字符的做法相冲突；例如，要匹配一个反斜杠字面量，我们可能不得不写``'\\'`` 作为模式字符串，因为正则表达式必须是 <code class="docutils literal notranslate"><span class="pre">\\</span></code>，而每个反斜杠必须在正则 Python 字符串字面量中表示为 <code class="docutils literal notranslate"><span class="pre">\\</span></code>。 另外，请注意 Python 在字符串字面中使用反斜杠时，任何无效的转义序列现在都会生成 <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">DeprecationWarning</span></code></a> ，将来会变成 <a class="reference internal" href="exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a>。 即使它是正则表达式的有效转义序列，这种行为也会发生。</p>
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<p>解决办法是对于正则表达式模式（patterns）使用 Python 的原始字符串表示法；在带有 <code class="docutils literal notranslate"><span class="pre">'r'</span></code> 前缀的字符串字面值中，反斜杠不必做任何特殊处理。 因此 <code class="docutils literal notranslate"><span class="pre">r"\n"</span></code> 表示包含 <code class="docutils literal notranslate"><span class="pre">'\'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">'n'</span></code> 两个字符的字符串，而 <code class="docutils literal notranslate"><span class="pre">"\n"</span></code> 则表示只包含一个换行符的字符串。 模式在 Python 代码中通常都使用原始字符串表示法。</p>
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<p>绝大多数正则表达式操作都提供为模块函数和方法，在 <a class="reference internal" href="#re-objects"><span class="std std-ref">编译正则表达式</span></a>. 这些函数是一个捷径，不需要先编译正则对象，但是损失了一些优化参数。</p>
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<div class="admonition seealso">
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<p class="admonition-title">参见</p>
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<p>第三方模块 <a class="reference external" href="https://pypi.org/project/regex/">regex</a> , 提供了与标准库 <a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> 模块兼容的 API 接口，同时，还提供了更多功能和更全面的 Unicode 支持。</p>
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</div>
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<section id="regular-expression-syntax">
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<span id="re-syntax"></span><h2>正则表达式语法<a class="headerlink" href="#regular-expression-syntax" title="永久链接至标题">¶</a></h2>
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<p>正则表达式（或 RE）指定了一组与之匹配的字符串；模块内的函数可以检查某个字符串是否与给定的正则表达式匹配（或者正则表达式是否匹配到字符串，这两种说法含义相同）。</p>
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<p>正则表达式可以拼接；如果 <em>A</em> 和 <em>B</em> 都是正则表达式，则 <em>AB</em> 也是正则表达式。通常，如果字符串 <em>p</em> 匹配 <em>A</em>，并且另一个字符串 <em>q</em> 匹配 <em>B</em>，那么 <em>pq</em> 可以匹配 AB。除非 <em>A</em> 或者 <em>B</em> 包含低优先级操作，<em>A</em> 和 <em>B</em> 存在边界条件；或者命名组引用。所以，复杂表达式可以很容易的从这里描述的简单源语表达式构建。更多正则表达式理论和实现，详见 the Friedl book <a class="reference internal" href="#frie09" id="id1"><span>[Frie09]</span></a> ，或者其他构建编译器的书籍。</p>
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<p>以下是正则表达式格式的简要说明。更详细的信息和演示，参考 <a class="reference internal" href="../howto/regex.html#regex-howto"><span class="std std-ref">正则表达式指南</span></a>。</p>
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<p>正则表达式可以包含普通或者特殊字符。绝大部分普通字符，比如 <code class="docutils literal notranslate"><span class="pre">'A'</span></code>, <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, 或者 <code class="docutils literal notranslate"><span class="pre">'0'</span></code>，都是最简单的正则表达式。它们就匹配自身。你可以拼接普通字符，所以 <code class="docutils literal notranslate"><span class="pre">last</span></code> 匹配字符串 <code class="docutils literal notranslate"><span class="pre">'last'</span></code>. （在这一节的其他部分，我们将用 <code class="docutils literal notranslate"><span class="pre">this</span> <span class="pre">special</span> <span class="pre">style</span></code> 这种方式表示正则表达式，通常不带引号，要匹配的字符串用 <code class="docutils literal notranslate"><span class="pre">'in</span> <span class="pre">single</span> <span class="pre">quotes'</span></code> ，单引号形式。）</p>
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<p>有些字符，比如 <code class="docutils literal notranslate"><span class="pre">'|'</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">'('</span></code>，属于特殊字符。 特殊字符既可以表示它的普通含义， 也可以影响它旁边的正则表达式的解释。</p>
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<p>重复修饰符 (<code class="docutils literal notranslate"><span class="pre">*</span></code>, <code class="docutils literal notranslate"><span class="pre">+</span></code>, <code class="docutils literal notranslate"><span class="pre">?</span></code>, <code class="docutils literal notranslate"><span class="pre">{m,n}</span></code>, 等) 不能直接嵌套。这样避免了非贪婪后缀 <code class="docutils literal notranslate"><span class="pre">?</span></code> 修饰符，和其他实现中的修饰符产生的多义性。要应用一个内层重复嵌套，可以使用括号。 比如，表达式 <code class="docutils literal notranslate"><span class="pre">(?:a{6})*</span></code> 匹配6个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> 字符重复任意次数。</p>
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<p>特殊字符有：</p>
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<dl class="simple" id="index-0">
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<dt><code class="docutils literal notranslate"><span class="pre">.</span></code></dt><dd><p>(点号) 在默认模式下，匹配除换行符以外的任意字符。 如果指定了旗标 <a class="reference internal" href="#re.DOTALL" title="re.DOTALL"><code class="xref py py-const docutils literal notranslate"><span class="pre">DOTALL</span></code></a> ，它将匹配包括换行符在内的任意字符。</p>
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</dd>
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</dl>
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<dl class="simple" id="index-1">
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<dt><code class="docutils literal notranslate"><span class="pre">^</span></code></dt><dd><p>(插入符) 匹配字符串的开头， 并且在 <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> 模式下也匹配换行后的首个符号。</p>
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</dd>
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</dl>
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<dl class="simple" id="index-2">
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<dt><code class="docutils literal notranslate"><span class="pre">$</span></code></dt><dd><p>匹配字符串尾或者在字符串尾的换行符的前一个字符，在 <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> 模式下也会匹配换行符之前的文本。 <code class="docutils literal notranslate"><span class="pre">foo</span></code> 匹配 'foo' 和 'foobar'，但正则表达式 <code class="docutils literal notranslate"><span class="pre">foo$</span></code> 只匹配 'foo'。 更有趣的是，在 <code class="docutils literal notranslate"><span class="pre">'foo1\nfoo2\n'</span></code> 中搜索 <code class="docutils literal notranslate"><span class="pre">foo.$</span></code>，通常匹配 'foo2'，但在 <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> 模式下可以匹配到 'foo1'；在 <code class="docutils literal notranslate"><span class="pre">'foo\n'</span></code> 中搜索 <code class="docutils literal notranslate"><span class="pre">$</span></code> 会找到两个（空的）匹配：一个在换行符之前，一个在字符串的末尾。</p>
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</dd>
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</dl>
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<dl class="simple" id="index-3">
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<dt><code class="docutils literal notranslate"><span class="pre">*</span></code></dt><dd><p>对它前面的正则式匹配0到任意次重复， 尽量多的匹配字符串。 <code class="docutils literal notranslate"><span class="pre">ab*</span></code> 会匹配 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>，<code class="docutils literal notranslate"><span class="pre">'ab'</span></code>，或者 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> 后面跟随任意个 <code class="docutils literal notranslate"><span class="pre">'b'</span></code>。</p>
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</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-4">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">+</span></code></dt><dd><p>对它前面的正则式匹配1到任意次重复。 <code class="docutils literal notranslate"><span class="pre">ab+</span></code> 会匹配 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> 后面跟随1个以上到任意个 <code class="docutils literal notranslate"><span class="pre">'b'</span></code>，它不会匹配 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-5">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">?</span></code></dt><dd><p>对它前面的正则式匹配0到1次重复。 <code class="docutils literal notranslate"><span class="pre">ab?</span></code> 会匹配 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">'ab'</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-6">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">+?</span></code>, <code class="docutils literal notranslate"><span class="pre">??</span></code></dt><dd><p><code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>，和 <code class="docutils literal notranslate"><span class="pre">'?'</span></code> 修饰符都是 <em class="dfn">贪婪的</em>；它们在字符串进行尽可能多的匹配。有时候并不需要这种行为。如果正则式 <code class="docutils literal notranslate"><span class="pre"><.*></span></code> 希望找到 <code class="docutils literal notranslate"><span class="pre">'<a></span> <span class="pre">b</span> <span class="pre"><c>'</span></code>，它将会匹配整个字符串，而不仅是 <code class="docutils literal notranslate"><span class="pre">'<a>'</span></code>。在修饰符之后添加 <code class="docutils literal notranslate"><span class="pre">?</span></code> 将使样式以 <em class="dfn">非贪婪`方式或者 :dfn:`最小</em> 方式进行匹配； 尽量 <em>少</em> 的字符将会被匹配。 使用正则式 <code class="docutils literal notranslate"><span class="pre"><.*?></span></code> 将会仅仅匹配 <code class="docutils literal notranslate"><span class="pre">'<a>'</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-7">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">{m}</span></code></dt><dd><p>对其之前的正则式指定匹配 <em>m</em> 个重复；少于 <em>m</em> 的话就会导致匹配失败。比如， <code class="docutils literal notranslate"><span class="pre">a{6}</span></code> 将匹配6个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> , 但是不能是5个。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}</span></code></dt><dd><p>对正则式进行 <em>m</em> 到 <em>n</em> 次匹配，在 <em>m</em> 和 <em>n</em> 之间取尽量多。 比如，<code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> 将匹配 3 到 5个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>。忽略 <em>m</em> 意为指定下界为0，忽略 <em>n</em> 指定上界为无限次。 比如 <code class="docutils literal notranslate"><span class="pre">a{4,}b</span></code> 将匹配 <code class="docutils literal notranslate"><span class="pre">'aaaab'</span></code> 或者1000个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> 尾随一个 <code class="docutils literal notranslate"><span class="pre">'b'</span></code>，但不能匹配 <code class="docutils literal notranslate"><span class="pre">'aaab'</span></code>。逗号不能省略，否则无法辨别修饰符应该忽略哪个边界。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}?</span></code></dt><dd><p>前一个修饰符的非贪婪模式，只匹配尽量少的字符次数。比如，对于 <code class="docutils literal notranslate"><span class="pre">'aaaaaa'</span></code>， <code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> 匹配 5个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> ，而 <code class="docutils literal notranslate"><span class="pre">a{3,5}?</span></code> 只匹配3个 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-8">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\</span></code></dt><dd><p>转义特殊字符（允许你匹配 <code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'?'</span></code>, 或者此类其他），或者表示一个特殊序列；特殊序列之后进行讨论。</p>
|
||
<p>如果你没有使用原始字符串（ <code class="docutils literal notranslate"><span class="pre">r'raw'</span></code> ）来表达样式，要牢记Python也使用反斜杠作为转义序列；如果转义序列不被Python的分析器识别，反斜杠和字符才能出现在字符串中。如果Python可以识别这个序列，那么反斜杠就应该重复两次。这将导致理解障碍，所以高度推荐，就算是最简单的表达式，也要使用原始字符串。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-9">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">[]</span></code></dt><dd><p>用于表示一个字符集合。在一个集合中：</p>
|
||
<ul class="simple">
|
||
<li><p>字符可以单独列出，比如 <code class="docutils literal notranslate"><span class="pre">[amk]</span></code> 匹配 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>， <code class="docutils literal notranslate"><span class="pre">'m'</span></code>， 或者 <code class="docutils literal notranslate"><span class="pre">'k'</span></code>。</p></li>
|
||
</ul>
|
||
<ul class="simple" id="index-10">
|
||
<li><p>可以表示字符范围，通过用 <code class="docutils literal notranslate"><span class="pre">'-'</span></code> 将两个字符连起来。比如 <code class="docutils literal notranslate"><span class="pre">[a-z]</span></code> 将匹配任何小写ASCII字符， <code class="docutils literal notranslate"><span class="pre">[0-5][0-9]</span></code> 将匹配从 <code class="docutils literal notranslate"><span class="pre">00</span></code> 到 <code class="docutils literal notranslate"><span class="pre">59</span></code> 的两位数字， <code class="docutils literal notranslate"><span class="pre">[0-9A-Fa-f]</span></code> 将匹配任何十六进制数位。 如果 <code class="docutils literal notranslate"><span class="pre">-</span></code> 进行了转义 （比如 <code class="docutils literal notranslate"><span class="pre">[a\-z]</span></code>）或者它的位置在首位或者末尾（如 <code class="docutils literal notranslate"><span class="pre">[-a]</span></code> 或 <code class="docutils literal notranslate"><span class="pre">[a-]</span></code>），它就只表示普通字符 <code class="docutils literal notranslate"><span class="pre">'-'</span></code>。</p></li>
|
||
<li><p>特殊字符在集合中会失去其特殊意义。比如 <code class="docutils literal notranslate"><span class="pre">[(+*)]</span></code> 只会匹配这几个字面字符之一 <code class="docutils literal notranslate"><span class="pre">'('</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>, <code class="docutils literal notranslate"><span class="pre">'*'</span></code>, or <code class="docutils literal notranslate"><span class="pre">')'</span></code>。</p></li>
|
||
</ul>
|
||
<ul class="simple" id="index-11">
|
||
<li><p>字符类如 <code class="docutils literal notranslate"><span class="pre">\w</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">\S</span></code> (如下定义) 在集合内可以接受，它们可以匹配的字符由 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 或者 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> 模式决定。</p></li>
|
||
</ul>
|
||
<ul class="simple" id="index-12">
|
||
<li><p>不在集合范围内的字符可以通过 <em class="dfn">取反</em> 来进行匹配。如果集合首字符是 <code class="docutils literal notranslate"><span class="pre">'^'</span></code> ，所有 <em>不</em> 在集合内的字符将会被匹配，比如 <code class="docutils literal notranslate"><span class="pre">[^5]</span></code> 将匹配所有字符，除了 <code class="docutils literal notranslate"><span class="pre">'5'</span></code>， <code class="docutils literal notranslate"><span class="pre">[^^]</span></code> 将匹配所有字符，除了 <code class="docutils literal notranslate"><span class="pre">'^'</span></code>. <code class="docutils literal notranslate"><span class="pre">^</span></code> 如果不在集合首位，就没有特殊含义。</p></li>
|
||
<li><p>在集合内要匹配一个字符 <code class="docutils literal notranslate"><span class="pre">']'</span></code>，有两种方法，要么就在它之前加上反斜杠，要么就把它放到集合首位。比如， <code class="docutils literal notranslate"><span class="pre">[()[\]{}]</span></code> 和 <code class="docutils literal notranslate"><span class="pre">[]()[{}]</span></code> 都可以匹配括号。</p></li>
|
||
</ul>
|
||
<ul class="simple">
|
||
<li><p><a class="reference external" href="https://unicode.org/reports/tr18/">Unicode Technical Standard #18</a> 里的嵌套集合和集合操作支持可能在未来添加。这将会改变语法，所以为了帮助这个改变，一个 <a class="reference internal" href="exceptions.html#FutureWarning" title="FutureWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">FutureWarning</span></code></a> 将会在有多义的情况里被 <code class="docutils literal notranslate"><span class="pre">raise</span></code>，包含以下几种情况，集合由 <code class="docutils literal notranslate"><span class="pre">'['</span></code> 开始，或者包含下列字符序列 <code class="docutils literal notranslate"><span class="pre">'--'</span></code>, <code class="docutils literal notranslate"><span class="pre">'&&'</span></code>, <code class="docutils literal notranslate"><span class="pre">'~~'</span></code>, 和 <code class="docutils literal notranslate"><span class="pre">'||'</span></code>。为了避免警告，需要将它们用反斜杠转义。</p></li>
|
||
</ul>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>如果一个字符串构建的语义在未来会改变的话，一个 <a class="reference internal" href="exceptions.html#FutureWarning" title="FutureWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">FutureWarning</span></code></a> 会 <code class="docutils literal notranslate"><span class="pre">raise</span></code> 。</p>
|
||
</div>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-13">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">|</span></code></dt><dd><p><code class="docutils literal notranslate"><span class="pre">A|B</span></code>， <em>A</em> 和 <em>B</em> 可以是任意正则表达式，创建一个正则表达式，匹配 <em>A</em> 或者 <em>B</em>. 任意个正则表达式可以用 <code class="docutils literal notranslate"><span class="pre">'|'</span></code> 连接。它也可以在组合（见下列）内使用。扫描目标字符串时， <code class="docutils literal notranslate"><span class="pre">'|'</span></code> 分隔开的正则样式从左到右进行匹配。当一个样式完全匹配时，这个分支就被接受。意思就是，一旦 <em>A</em> 匹配成功， <em>B</em> 就不再进行匹配，即便它能产生一个更好的匹配。或者说，<code class="docutils literal notranslate"><span class="pre">'|'</span></code> 操作符绝不贪婪。 如果要匹配 <code class="docutils literal notranslate"><span class="pre">'|'</span></code> 字符，使用 <code class="docutils literal notranslate"><span class="pre">\|</span></code>， 或者把它包含在字符集里，比如 <code class="docutils literal notranslate"><span class="pre">[|]</span></code>.</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-14">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(...)</span></code></dt><dd><p>（组合），匹配括号内的任意正则表达式，并标识出组合的开始和结尾。匹配完成后，组合的内容可以被获取，并可以在之后用 <code class="docutils literal notranslate"><span class="pre">\number</span></code> 转义序列进行再次匹配，之后进行详细说明。要匹配字符 <code class="docutils literal notranslate"><span class="pre">'('</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">')'</span></code>, 用 <code class="docutils literal notranslate"><span class="pre">\(</span></code> 或 <code class="docutils literal notranslate"><span class="pre">\)</span></code>, 或者把它们包含在字符集合里: <code class="docutils literal notranslate"><span class="pre">[(]</span></code>, <code class="docutils literal notranslate"><span class="pre">[)]</span></code>.</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-15">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?…)</span></code></dt><dd><p>这是个扩展标记法 （一个 <code class="docutils literal notranslate"><span class="pre">'?'</span></code> 跟随 <code class="docutils literal notranslate"><span class="pre">'('</span></code> 并无含义）。 <code class="docutils literal notranslate"><span class="pre">'?'</span></code> 后面的第一个字符决定了这个构建采用什么样的语法。这种扩展通常并不创建新的组合； <code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code> 是唯一的例外。 以下是目前支持的扩展。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?aiLmsux)</span></code></dt><dd><p>( <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'i'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code>, <code class="docutils literal notranslate"><span class="pre">'m'</span></code>, <code class="docutils literal notranslate"><span class="pre">'s'</span></code>, <code class="docutils literal notranslate"><span class="pre">'u'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code> 中的一个或多个) 这个组合匹配一个空字符串；这些字符对正则表达式设置以下标记 <a class="reference internal" href="#re.A" title="re.A"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.A</span></code></a> (只匹配ASCII字符), <a class="reference internal" href="#re.I" title="re.I"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.I</span></code></a> (忽略大小写), <a class="reference internal" href="#re.L" title="re.L"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.L</span></code></a> (语言依赖), <a class="reference internal" href="#re.M" title="re.M"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.M</span></code></a> (多行模式), <a class="reference internal" href="#re.S" title="re.S"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.S</span></code></a> (点dot匹配全部字符), <code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code> (Unicode匹配), and <a class="reference internal" href="#re.X" title="re.X"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.X</span></code></a> (冗长模式)。 (这些标记在 <a class="reference internal" href="#contents-of-module-re"><span class="std std-ref">模块内容</span></a> 中描述) 如果你想将这些标记包含在正则表达式中，这个方法就很有用，免去了在 <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> 中传递 <em>flag</em> 参数。标记应该在表达式字符串首位表示。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-16">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?:…)</span></code></dt><dd><p>正则括号的非捕获版本。 匹配在括号内的任何正则表达式，但该分组所匹配的子字符串 <em>不能</em> 在执行匹配后被获取或是之后在模式中被引用。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?aiLmsux-imsx:…)</span></code></dt><dd><p>(<code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'i'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code>, <code class="docutils literal notranslate"><span class="pre">'m'</span></code>, <code class="docutils literal notranslate"><span class="pre">'s'</span></code>, <code class="docutils literal notranslate"><span class="pre">'u'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code> 中的0或者多个， 之后可选跟随 <code class="docutils literal notranslate"><span class="pre">'-'</span></code> 在后面跟随 <code class="docutils literal notranslate"><span class="pre">'i'</span></code> , <code class="docutils literal notranslate"><span class="pre">'m'</span></code> , <code class="docutils literal notranslate"><span class="pre">'s'</span></code> , <code class="docutils literal notranslate"><span class="pre">'x'</span></code> 中的一到多个 .) 这些字符为表达式的其中一部分 <em>设置</em> 或者 <em>去除</em> 相应标记 <a class="reference internal" href="#re.A" title="re.A"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.A</span></code></a> (只匹配ASCII), <a class="reference internal" href="#re.I" title="re.I"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.I</span></code></a> (忽略大小写), <a class="reference internal" href="#re.L" title="re.L"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.L</span></code></a> (语言依赖), <a class="reference internal" href="#re.M" title="re.M"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.M</span></code></a> (多行), <a class="reference internal" href="#re.S" title="re.S"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.S</span></code></a> (点匹配所有字符), <code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code> (Unicode匹配), and <a class="reference internal" href="#re.X" title="re.X"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.X</span></code></a> (冗长模式)。(标记描述在 <a class="reference internal" href="#contents-of-module-re"><span class="std std-ref">模块内容</span></a> .)</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code> and <code class="docutils literal notranslate"><span class="pre">'u'</span></code> 作为内联标记是相互排斥的， 所以它们不能结合在一起，或者跟随 <code class="docutils literal notranslate"><span class="pre">'-'</span></code> 。 当他们中的某个出现在内联组中，它就覆盖了括号组内的匹配模式。在Unicode样式中， <code class="docutils literal notranslate"><span class="pre">(?a:...)</span></code> 切换为 只匹配ASCII， <code class="docutils literal notranslate"><span class="pre">(?u:...)</span></code> 切换为Unicode匹配 (默认). 在byte样式中 <code class="docutils literal notranslate"><span class="pre">(?L:...)</span></code> 切换为语言依赖模式， <code class="docutils literal notranslate"><span class="pre">(?a:...)</span></code> 切换为 只匹配ASCII (默认)。这种方式只覆盖组合内匹配，括号外的匹配模式不受影响。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.6 新版功能.</span></p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>符号 <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">'u'</span></code> 同样可以用在一个组合内。</p>
|
||
</div>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-17">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?P<name>…)</span></code></dt><dd><p>（命名组合）类似正则组合，但是匹配到的子串组在外部是通过定义的 <em>name</em> 来获取的。组合名必须是有效的Python标识符，并且每个组合名只能用一个正则表达式定义，只能定义一次。一个符号组合同样是一个数字组合，就像这个组合没有被命名一样。</p>
|
||
<p>命名组合可以在三种上下文中引用。如果样式是 <code class="docutils literal notranslate"><span class="pre">(?P<quote>['"]).*?(?P=quote)</span></code> （也就是说，匹配单引号或者双引号括起来的字符串)：</p>
|
||
<table class="docutils align-default">
|
||
<colgroup>
|
||
<col style="width: 53%" />
|
||
<col style="width: 47%" />
|
||
</colgroup>
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p>引用组合 "quote" 的上下文</p></th>
|
||
<th class="head"><p>引用方法</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p>在正则式自身内</p></td>
|
||
<td><ul class="simple">
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">(?P=quote)</span></code> (如示)</p></li>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">\1</span></code></p></li>
|
||
</ul>
|
||
</td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p>处理匹配对象 <em>m</em></p></td>
|
||
<td><ul class="simple">
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">m.group('quote')</span></code></p></li>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">m.end('quote')</span></code> (等)</p></li>
|
||
</ul>
|
||
</td>
|
||
</tr>
|
||
<tr class="row-even"><td><p>传递到 <code class="docutils literal notranslate"><span class="pre">re.sub()</span></code> 里的 <em>repl</em> 参数中</p></td>
|
||
<td><ul class="simple">
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">\g<quote></span></code></p></li>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">\g<1></span></code></p></li>
|
||
<li><p><code class="docutils literal notranslate"><span class="pre">\1</span></code></p></li>
|
||
</ul>
|
||
</td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-18">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?P=name)</span></code></dt><dd><p>反向引用一个命名组合；它匹配前面那个叫 <em>name</em> 的命名组中匹配到的串同样的字串。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-19">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?#…)</span></code></dt><dd><p>注释；里面的内容会被忽略。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-20">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?=…)</span></code></dt><dd><p>当 <code class="docutils literal notranslate"><span class="pre">…</span></code> 匹配时，匹配成功，但不消耗字符串中的任何字符。这个叫做 <em class="dfn">前视断言</em> （lookahead assertion）。比如， <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?=Asimov)</span></code> 将会匹配 <code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> ，仅当其后紧跟 <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code> 。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-21">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?!…)</span></code></dt><dd><p>当 <code class="docutils literal notranslate"><span class="pre">…</span></code> 不匹配时，匹配成功。这个叫 <em class="dfn">否定型前视断言</em> （negative lookahead assertion）。例如， <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?!Asimov)</span></code> 将会匹配 <code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> ，仅当它后面 <em>不是</em> <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code> 。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-22">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?<=…)</span></code></dt><dd><p>如果 <code class="docutils literal notranslate"><span class="pre">...</span></code> 的匹配内容出现在当前位置的左侧，则匹配。这叫做 <em class="dfn">肯定型后视断言</em> （positive lookbehind assertion）。 <code class="docutils literal notranslate"><span class="pre">(?<=abc)def</span></code> 将会在 <code class="docutils literal notranslate"><span class="pre">'abcdef'</span></code> 中找到一个匹配，因为后视会回退3个字符并检查内部表达式是否匹配。内部表达式（匹配的内容）必须是固定长度的，意思就是 <code class="docutils literal notranslate"><span class="pre">abc</span></code> 或 <code class="docutils literal notranslate"><span class="pre">a|b</span></code> 是允许的，但是 <code class="docutils literal notranslate"><span class="pre">a*</span></code> 和 <code class="docutils literal notranslate"><span class="pre">a{3,4}</span></code> 不可以。注意，以肯定型后视断言开头的正则表达式，匹配项一般不会位于搜索字符串的开头。很可能你应该使用 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 函数，而不是 <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> 函数：</p>
|
||
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">re</span>
|
||
<span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'(?<=abc)def'</span><span class="p">,</span> <span class="s1">'abcdef'</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
|
||
<span class="go">'def'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>这个例子搜索一个跟随在连字符后的单词：</p>
|
||
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="sa">r</span><span class="s1">'(?<=-)\w+'</span><span class="p">,</span> <span class="s1">'spam-egg'</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
|
||
<span class="go">'egg'</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>添加定长组合引用的支持。</p>
|
||
</div>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-23">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?<!…)</span></code></dt><dd><p>如果 <code class="docutils literal notranslate"><span class="pre">...</span></code> 的匹配内容没有出现在当前位置的左侧，则匹配。这个叫做 <em class="dfn">否定型后视断言</em> （negative lookbehind assertion）。类似于肯定型后视断言，内部表达式（匹配的内容）必须是固定长度的。以否定型后视断言开头的正则表达式，匹配项可能位于搜索字符串的开头。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">(?(id/name)yes-pattern|no-pattern)</span></code></dt><dd><p>如果给定的 <em>id</em> 或 <em>name</em> 存在，将会尝试匹配 <code class="docutils literal notranslate"><span class="pre">yes-pattern</span></code> ，否则就尝试匹配 <code class="docutils literal notranslate"><span class="pre">no-pattern</span></code>，<code class="docutils literal notranslate"><span class="pre">no-pattern</span></code> 可选，也可以被忽略。比如， <code class="docutils literal notranslate"><span class="pre">(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)</span></code> 是一个email样式匹配，将匹配 <code class="docutils literal notranslate"><span class="pre">'<user@host.com>'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'user@host.com'</span></code> ，但不会匹配 <code class="docutils literal notranslate"><span class="pre">'<user@host.com'</span></code> ，也不会匹配 <code class="docutils literal notranslate"><span class="pre">'user@host.com>'</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
<p>由 <code class="docutils literal notranslate"><span class="pre">'\'</span></code> 和一个字符组成的特殊序列在以下列出。 如果普通字符不是ASCII数位或者ASCII字母，那么正则样式将匹配第二个字符。比如，<code class="docutils literal notranslate"><span class="pre">\$</span></code> 匹配字符 <code class="docutils literal notranslate"><span class="pre">'$'</span></code>.</p>
|
||
<dl class="simple" id="index-24">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\number</span></code></dt><dd><p>匹配数字代表的组合。每个括号是一个组合，组合从1开始编号。比如 <code class="docutils literal notranslate"><span class="pre">(.+)</span> <span class="pre">\1</span></code> 匹配 <code class="docutils literal notranslate"><span class="pre">'the</span> <span class="pre">the'</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">'55</span> <span class="pre">55'</span></code>, 但不会匹配 <code class="docutils literal notranslate"><span class="pre">'thethe'</span></code> (注意组合后面的空格)。这个特殊序列只能用于匹配前面99个组合。如果 <em>number</em> 的第一个数位是0， 或者 <em>number</em> 是三个八进制数，它将不会被看作是一个组合，而是八进制的数字值。在 <code class="docutils literal notranslate"><span class="pre">'['</span></code> 和 <code class="docutils literal notranslate"><span class="pre">']'</span></code> 字符集合内，任何数字转义都被看作是字符。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-25">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\A</span></code></dt><dd><p>只匹配字符串开始。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl id="index-26">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\b</span></code></dt><dd><p>匹配空字符串，但只在单词开始或结尾的位置。一个单词被定义为一个单词字符的序列。注意，通常 <code class="docutils literal notranslate"><span class="pre">\b</span></code> 定义为 <code class="docutils literal notranslate"><span class="pre">\w</span></code> 和 <code class="docutils literal notranslate"><span class="pre">\W</span></code> 字符之间，或者 <code class="docutils literal notranslate"><span class="pre">\w</span></code> 和字符串开始/结尾的边界， 意思就是 <code class="docutils literal notranslate"><span class="pre">r'\bfoo\b'</span></code> 匹配 <code class="docutils literal notranslate"><span class="pre">'foo'</span></code>, <code class="docutils literal notranslate"><span class="pre">'foo.'</span></code>, <code class="docutils literal notranslate"><span class="pre">'(foo)'</span></code>, <code class="docutils literal notranslate"><span class="pre">'bar</span> <span class="pre">foo</span> <span class="pre">baz'</span></code> 但不匹配 <code class="docutils literal notranslate"><span class="pre">'foobar'</span></code> 或者 <code class="docutils literal notranslate"><span class="pre">'foo3'</span></code>。</p>
|
||
<p>默认情况下，Unicode字母和数字是在Unicode样式中使用的，但是可以用 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标记来更改。如果 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> 标记被设置的话，词的边界是由当前语言区域设置决定的，<code class="docutils literal notranslate"><span class="pre">\b</span></code> 表示退格字符，以便与Python字符串文本兼容。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-27">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\B</span></code></dt><dd><p>匹配空字符串，但 <em>不</em> 能在词的开头或者结尾。意思就是 <code class="docutils literal notranslate"><span class="pre">r'py\B'</span></code> 匹配 <code class="docutils literal notranslate"><span class="pre">'python'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py3'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py2'</span></code>, 但不匹配 <code class="docutils literal notranslate"><span class="pre">'py'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py.'</span></code>, 或者 <code class="docutils literal notranslate"><span class="pre">'py!'</span></code>. <code class="docutils literal notranslate"><span class="pre">\B</span></code> 是 <code class="docutils literal notranslate"><span class="pre">\b</span></code> 的取非，所以Unicode样式的词语是由Unicode字母，数字或下划线构成的，虽然可以用 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标志来改变。如果使用了 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> 标志，则词的边界由当前语言区域设置。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-28">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\d</span></code></dt><dd><dl class="simple">
|
||
<dt>对于 Unicode (str) 样式：</dt><dd><p>匹配任何Unicode十进制数（就是在Unicode字符目录[Nd]里的字符）。这包括了 <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code> ，和很多其他的数字字符。如果设置了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标志，就只匹配 <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code> 。</p>
|
||
</dd>
|
||
<dt>对于8位(bytes)样式：</dt><dd><p>匹配任何十进制数，就是 <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code>。</p>
|
||
</dd>
|
||
</dl>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-29">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\D</span></code></dt><dd><p>匹配任何非十进制数字的字符。就是 <code class="docutils literal notranslate"><span class="pre">\d</span></code> 取非。 如果设置了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标志，就相当于 <code class="docutils literal notranslate"><span class="pre">[^0-9]</span></code> 。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-30">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\s</span></code></dt><dd><dl class="simple">
|
||
<dt>对于 Unicode (str) 样式：</dt><dd><p>匹配任何Unicode空白字符（包括 <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code> ，还有很多其他字符，比如不同语言排版规则约定的不换行空格）。如果 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 被设置，就只匹配 <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code> 。</p>
|
||
</dd>
|
||
<dt>对于8位(bytes)样式：</dt><dd><p>匹配ASCII中的空白字符，就是 <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code> 。</p>
|
||
</dd>
|
||
</dl>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-31">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\S</span></code></dt><dd><p>匹配任何非空白字符。就是 <code class="docutils literal notranslate"><span class="pre">\s</span></code> 取非。如果设置了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标志，就相当于 <code class="docutils literal notranslate"><span class="pre">[^</span> <span class="pre">\t\n\r\f\v]</span></code> 。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-32">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\w</span></code></dt><dd><dl class="simple">
|
||
<dt>对于 Unicode (str) 样式：</dt><dd><p>匹配Unicode词语的字符，包含了可以构成词语的绝大部分字符，也包括数字和下划线。如果设置了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标志，就只匹配 <code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code> 。</p>
|
||
</dd>
|
||
<dt>对于8位(bytes)样式：</dt><dd><p>匹配ASCII字符中的数字和字母和下划线，就是 <code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code> 。如果设置了 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> 标记，就匹配当前语言区域的数字和字母和下划线。</p>
|
||
</dd>
|
||
</dl>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-33">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\W</span></code></dt><dd><p>匹配非单词字符的字符。这与 <code class="docutils literal notranslate"><span class="pre">\w</span></code> 正相反。如果使用了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 旗标，这就等价于 <code class="docutils literal notranslate"><span class="pre">[^a-zA-Z0-9_]</span></code>。如果使用了 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> 旗标，则会匹配当前区域中既非字母数字也非下划线的字符。</p>
|
||
</dd>
|
||
</dl>
|
||
<dl class="simple" id="index-34">
|
||
<dt><code class="docutils literal notranslate"><span class="pre">\Z</span></code></dt><dd><p>只匹配字符串尾。</p>
|
||
</dd>
|
||
</dl>
|
||
<p id="index-35">绝大部分Python的标准转义字符也被正则表达式分析器支持。:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span>\<span class="n">a</span> \<span class="n">b</span> \<span class="n">f</span> \<span class="n">n</span>
|
||
\<span class="n">N</span> \<span class="n">r</span> \<span class="n">t</span> \<span class="n">u</span>
|
||
\<span class="n">U</span> \<span class="n">v</span> \<span class="n">x</span> \\
|
||
</pre></div>
|
||
</div>
|
||
<p>（注意 <code class="docutils literal notranslate"><span class="pre">\b</span></code> 被用于表示词语的边界，它只在字符集合内表示退格，比如 <code class="docutils literal notranslate"><span class="pre">[\b]</span></code> 。）</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">'\u'</span></code>, <code class="docutils literal notranslate"><span class="pre">'\U'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">'\N'</span></code> 转义序列只在 Unicode 模式中可被识别。 在 bytes 模式中它们会导致错误。 未知的 ASCII 字母转义序列保留在未来使用，会被当作错误来处理。</p>
|
||
<p>八进制转义包含为一个有限形式。如果首位数字是 0， 或者有三个八进制数位，那么就认为它是八进制转义。其他的情况，就看作是组引用。对于字符串文本，八进制转义最多有三个数位长。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.3 版更改: </span>增加了 <code class="docutils literal notranslate"><span class="pre">'\u'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">'\U'</span></code> 转义序列。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span>由 <code class="docutils literal notranslate"><span class="pre">'\'</span></code> 和一个ASCII字符组成的未知转义会被看成错误。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.8 版更改: </span>添加了 <code class="docutils literal notranslate"><span class="pre">'\N{name}'</span></code> 转义序列。 与在字符串字面值中一样，它扩展了命名 Unicode 字符 (例如 <code class="docutils literal notranslate"><span class="pre">'\N{EM</span> <span class="pre">DASH}'</span></code>)。</p>
|
||
</div>
|
||
</section>
|
||
<section id="module-contents">
|
||
<span id="contents-of-module-re"></span><h2>模块内容<a class="headerlink" href="#module-contents" title="永久链接至标题">¶</a></h2>
|
||
<p>模块定义了几个函数、常量，和一个异常。有些函数是编译后的正则表达式方法的简化版本（少了一些特性）。重要的应用程序大多会在使用前先编译正则表达式。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span>标志常量现在是 <code class="xref py py-class docutils literal notranslate"><span class="pre">RegexFlag</span></code> 类的实例，这个类是 <a class="reference internal" href="enum.html#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">enum.IntFlag</span></code></a> 的子类。</p>
|
||
</div>
|
||
<dl class="function">
|
||
<dt id="re.compile">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">compile</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.compile" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>将正则表达式的样式编译为一个 <a class="reference internal" href="#re-objects"><span class="std std-ref">正则表达式对象</span></a> （正则对象），可以用于匹配，通过这个对象的方法 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a>, <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 以及其他如下描述。</p>
|
||
<p>这个表达式的行为可以通过指定 <em>标记</em> 的值来改变。值可以是以下任意变量，可以通过位的OR操作来结合（ <code class="docutils literal notranslate"><span class="pre">|</span></code> 操作符）。</p>
|
||
<p>序列</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">prog</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="n">pattern</span><span class="p">)</span>
|
||
<span class="n">result</span> <span class="o">=</span> <span class="n">prog</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">string</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>等价于</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">result</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果需要多次使用这个正则表达式的话，使用 <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> 和保存这个正则对象以便复用，可以让程序更加高效。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>通过 <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> 编译后的样式，和模块级的函数会被缓存， 所以少数的正则表达式使用无需考虑编译的问题。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.A">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">A</code><a class="headerlink" href="#re.A" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.ASCII">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">ASCII</code><a class="headerlink" href="#re.ASCII" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>让 <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code>, <code class="docutils literal notranslate"><span class="pre">\d</span></code>, <code class="docutils literal notranslate"><span class="pre">\D</span></code>, <code class="docutils literal notranslate"><span class="pre">\s</span></code> 和 <code class="docutils literal notranslate"><span class="pre">\S</span></code> 只匹配ASCII，而不是Unicode。这只对Unicode样式有效，会被byte样式忽略。相当于前面语法中的内联标志 <code class="docutils literal notranslate"><span class="pre">(?a)</span></code> 。</p>
|
||
<p>注意，为了保持向后兼容， <code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code> 标记依然存在（还有他的同义 <code class="xref py py-const docutils literal notranslate"><span class="pre">re.UNICODE</span></code> 和嵌入形式 <code class="docutils literal notranslate"><span class="pre">(?u)</span></code> ) ， 但是这些在 Python 3 是冗余的，因为默认字符串已经是Unicode了（并且Unicode匹配不允许byte出现)。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.DEBUG">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">DEBUG</code><a class="headerlink" href="#re.DEBUG" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>显示编译时的debug信息，没有内联标记。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.I">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">I</code><a class="headerlink" href="#re.I" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.IGNORECASE">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">IGNORECASE</code><a class="headerlink" href="#re.IGNORECASE" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>进行忽略大小写匹配；表达式如 <code class="docutils literal notranslate"><span class="pre">[A-Z]</span></code> 也会匹配小写字符。Unicode匹配（比如 <code class="docutils literal notranslate"><span class="pre">Ü</span></code> 匹配 <code class="docutils literal notranslate"><span class="pre">ü</span></code>）同样有用，除非设置了 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.ASCII</span></code></a> 标记来禁用非ASCII匹配。当前语言区域不会改变这个标记，除非设置了 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.LOCALE</span></code></a> 标记。这个相当于内联标记 <code class="docutils literal notranslate"><span class="pre">(?i)</span></code> 。</p>
|
||
<p>注意，当设置了 <a class="reference internal" href="#re.IGNORECASE" title="re.IGNORECASE"><code class="xref py py-const docutils literal notranslate"><span class="pre">IGNORECASE</span></code></a> 标记，搜索Unicode样式 <code class="docutils literal notranslate"><span class="pre">[a-z]</span></code> 或 <code class="docutils literal notranslate"><span class="pre">[A-Z]</span></code> 的结合时，它将会匹配52个ASCII字符和4个额外的非ASCII字符： 'İ' (U+0130, 拉丁大写的 I 带个点在上面), 'ı' (U+0131, 拉丁小写没有点的 I ), 'ſ' (U+017F, 拉丁小写长 s) and 'K' (U+212A, 开尔文符号).如果使用 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> 标记，就只匹配 'a' 到 'z' 和 'A' 到 'Z' 。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.L">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">L</code><a class="headerlink" href="#re.L" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.LOCALE">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">LOCALE</code><a class="headerlink" href="#re.LOCALE" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>由当前语言区域决定 <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code> 和大小写敏感匹配。这个标记只能对byte样式有效。这个标记不推荐使用，因为语言区域机制很不可靠，它一次只能处理一个 "习惯”，而且只对8位字节有效。Unicode匹配在Python 3 里默认启用，并可以处理不同语言。 这个对应内联标记 <code class="docutils literal notranslate"><span class="pre">(?L)</span></code> 。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span><a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.LOCALE</span></code></a> 只能用于byte样式，而且不能和 <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.ASCII</span></code></a> 一起用。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>设置了 <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.LOCALE</span></code></a> 标记的编译正则对象不再在编译时依赖语言区域设置。语言区域设置只在匹配的时候影响其结果。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.M">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">M</code><a class="headerlink" href="#re.M" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.MULTILINE">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">MULTILINE</code><a class="headerlink" href="#re.MULTILINE" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>设置以后，样式字符 <code class="docutils literal notranslate"><span class="pre">'^'</span></code> 匹配字符串的开始，和每一行的开始（换行符后面紧跟的符号）；样式字符 <code class="docutils literal notranslate"><span class="pre">'$'</span></code> 匹配字符串尾，和每一行的结尾（换行符前面那个符号）。默认情况下，<code class="docutils literal notranslate"><span class="pre">’^’</span></code> 匹配字符串头，<code class="docutils literal notranslate"><span class="pre">'$'</span></code> 匹配字符串尾。对应内联标记 <code class="docutils literal notranslate"><span class="pre">(?m)</span></code> 。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.S">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">S</code><a class="headerlink" href="#re.S" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.DOTALL">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">DOTALL</code><a class="headerlink" href="#re.DOTALL" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>让 <code class="docutils literal notranslate"><span class="pre">'.'</span></code> 特殊字符匹配任何字符，包括换行符；如果没有这个标记，<code class="docutils literal notranslate"><span class="pre">'.'</span></code> 就匹配 <em>除了</em> 换行符的其他任意字符。对应内联标记 <code class="docutils literal notranslate"><span class="pre">(?s)</span></code> 。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="data">
|
||
<dt id="re.X">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">X</code><a class="headerlink" href="#re.X" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.VERBOSE">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">VERBOSE</code><a class="headerlink" href="#re.VERBOSE" title="永久链接至目标">¶</a></dt>
|
||
<dd><p id="index-36">这个标记允许你编写更具可读性更友好的正则表达式。通过分段和添加注释。空白符号会被忽略，除非在一个字符集合当中或者由反斜杠转义，或者在 <code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">(?:</span></code> or <code class="docutils literal notranslate"><span class="pre">(?P<…></span></code> 分组之内。当一个行内有 <code class="docutils literal notranslate"><span class="pre">#</span></code> 不在字符集和转义序列，那么它之后的所有字符都是注释。</p>
|
||
<p>意思就是下面两个正则表达式等价地匹配一个十进制数字：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">a</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"""\d + # the integral part</span>
|
||
<span class="s2"> \. # the decimal point</span>
|
||
<span class="s2"> \d * # some fractional digits"""</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">X</span><span class="p">)</span>
|
||
<span class="n">b</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\d+\.\d*"</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>对应内联标记 <code class="docutils literal notranslate"><span class="pre">(?x)</span></code> 。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.search">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">search</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.search" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>扫描整个 <em>字符串</em> 找到匹配样式的第一个位置，并返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a>。如果没有匹配，就返回一个 <code class="docutils literal notranslate"><span class="pre">None</span></code> ； 注意这和找到一个零长度匹配是不同的。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.match">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">match</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>如果 <em>string</em> 开始的0或者多个字符匹配到了正则表达式样式，就返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 。 如果没有匹配，就返回 <code class="docutils literal notranslate"><span class="pre">None</span></code> ；注意它跟零长度匹配是不同的。</p>
|
||
<p>注意即便是 <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> 多行模式， <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> 也只匹配字符串的开始位置，而不匹配每行开始。</p>
|
||
<p>如果你想定位 <em>string</em> 的任何位置，使用 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 来替代（也可参考 <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a> ）</p>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.fullmatch">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">fullmatch</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.fullmatch" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>如果整个 <em>string</em> 匹配到正则表达式样式，就返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 。 否则就返回一个 <code class="docutils literal notranslate"><span class="pre">None</span></code> ；注意这跟零长度匹配是不同的。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.4 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.split">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">split</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">maxsplit=0</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.split" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>用 <em>pattern</em> 分开 <em>string</em> 。 如果在 <em>pattern</em> 中捕获到括号，那么所有的组里的文字也会包含在列表里。如果 <em>maxsplit</em> 非零， 最多进行 <em>maxsplit</em> 次分隔， 剩下的字符全部返回到列表的最后一个元素。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\W+'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">)</span>
|
||
<span class="go">['Words', 'words', 'words', '']</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'(\W+)'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">)</span>
|
||
<span class="go">['Words', ', ', 'words', ', ', 'words', '.', '']</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\W+'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
|
||
<span class="go">['Words', 'words, words.']</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">'[a-f]+'</span><span class="p">,</span> <span class="s1">'0a3B9'</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
|
||
<span class="go">['0', '3', '9']</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果分隔符里有捕获组合，并且匹配到字符串的开始，那么结果将会以一个空字符串开始。对于结尾也是一样</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'(\W+)'</span><span class="p">,</span> <span class="s1">'...words, words...'</span><span class="p">)</span>
|
||
<span class="go">['', '...', 'words', ', ', 'words', '...', '']</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>这样的话，分隔组将会出现在结果列表中同样的位置。</p>
|
||
<p>样式的空匹配仅在与前一个空匹配不相邻时才会拆分字符串。</p>
|
||
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\b'</span><span class="p">,</span> <span class="s1">'Words, words, words.'</span><span class="p">)</span>
|
||
<span class="go">['', 'Words', ', ', 'words', ', ', 'words', '.']</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\W*'</span><span class="p">,</span> <span class="s1">'...words...'</span><span class="p">)</span>
|
||
<span class="go">['', '', 'w', 'o', 'r', 'd', 's', '', '']</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">'(\W*)'</span><span class="p">,</span> <span class="s1">'...words...'</span><span class="p">)</span>
|
||
<span class="go">['', '...', '', '', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '', '', '']</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.1 版更改: </span>增加了可选标记参数。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>增加了空字符串的样式分隔。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.findall">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">findall</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.findall" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>对 <em>string</em> 返回一个不重复的 <em>pattern</em> 的匹配列表， <em>string</em> 从左到右进行扫描，匹配按找到的顺序返回。如果样式里存在一到多个组，就返回一个组合列表；就是一个元组的列表（如果样式里有超过一个组合的话）。空匹配也会包含在结果里。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>非空匹配现在可以在前一个空匹配之后出现了。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.finditer">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">finditer</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">string</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.finditer" title="永久链接至目标">¶</a></dt>
|
||
<dd><p><em>pattern</em> 在 <em>string</em> 里所有的非重复匹配，返回为一个迭代器 <a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> 保存了 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 。 <em>string</em> 从左到右扫描，匹配按顺序排列。空匹配也包含在结果里。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>非空匹配现在可以在前一个空匹配之后出现了。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.sub">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">sub</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">repl</em>, <em class="sig-param">string</em>, <em class="sig-param">count=0</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.sub" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回通过使用 <em>repl</em> 替换在 <em>string</em> 最左边非重叠出现的 <em>pattern</em> 而获得的字符串。 如果样式没有找到，则不加改变地返回 <em>string</em>。 <em>repl</em> 可以是字符串或函数；如为字符串，则其中任何反斜杠转义序列都会被处理。 也就是说，<code class="docutils literal notranslate"><span class="pre">\n</span></code> 会被转换为一个换行符，<code class="docutils literal notranslate"><span class="pre">\r</span></code> 会被转换为一个回车符，依此类推。 未知的 ASCII 字符转义序列保留在未来使用，会被当作错误来处理。 其他未知转义序列例如 <code class="docutils literal notranslate"><span class="pre">\&</span></code> 会保持原样。 向后引用像是 <code class="docutils literal notranslate"><span class="pre">\6</span></code> 会用样式中第 6 组所匹配到的子字符串来替换。 例如:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):'</span><span class="p">,</span>
|
||
<span class="gp">... </span> <span class="sa">r</span><span class="s1">'static PyObject*\npy_\1(void)\n{'</span><span class="p">,</span>
|
||
<span class="gp">... </span> <span class="s1">'def myfunc():'</span><span class="p">)</span>
|
||
<span class="go">'static PyObject*\npy_myfunc(void)\n{'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果 <em>repl</em> 是一个函数，那它会对每个非重复的 <em>pattern</em> 的情况调用。这个函数只能有一个 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 参数，并返回一个替换后的字符串。比如</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">dashrepl</span><span class="p">(</span><span class="n">matchobj</span><span class="p">):</span>
|
||
<span class="gp">... </span> <span class="k">if</span> <span class="n">matchobj</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="o">==</span> <span class="s1">'-'</span><span class="p">:</span> <span class="k">return</span> <span class="s1">' '</span>
|
||
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span> <span class="k">return</span> <span class="s1">'-'</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="s1">'-{1,2}'</span><span class="p">,</span> <span class="n">dashrepl</span><span class="p">,</span> <span class="s1">'pro----gram-files'</span><span class="p">)</span>
|
||
<span class="go">'pro--gram files'</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">'\sAND\s'</span><span class="p">,</span> <span class="s1">' & '</span><span class="p">,</span> <span class="s1">'Baked Beans And Spam'</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
|
||
<span class="go">'Baked Beans & Spam'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>样式可以是一个字符串或者一个 <a class="reference internal" href="#re-objects"><span class="std std-ref">样式对象</span></a> 。</p>
|
||
<p>可选参数 <em>count</em> 是要替换的最大次数；<em>count</em> 必须是非负整数。如果省略这个参数或设为 0，所有的匹配都会被替换。 样式的空匹配仅在与前一个空匹配不相邻时才会被替换，所以 <code class="docutils literal notranslate"><span class="pre">sub('x*',</span> <span class="pre">'-',</span> <span class="pre">'abxd')</span></code> 返回 <code class="docutils literal notranslate"><span class="pre">'-a-b--d-'</span></code> 。</p>
|
||
<p id="index-37">在字符串类型的 <em>repl</em> 参数里，如上所述的转义和向后引用中，<code class="docutils literal notranslate"><span class="pre">\g<name></span></code> 会使用命名组合 <code class="docutils literal notranslate"><span class="pre">name</span></code>，（在 <code class="docutils literal notranslate"><span class="pre">(?P<name>…)</span></code> 语法中定义） <code class="docutils literal notranslate"><span class="pre">\g<number></span></code> 会使用数字组；<code class="docutils literal notranslate"><span class="pre">\g<2></span></code> 就是 <code class="docutils literal notranslate"><span class="pre">\2</span></code>，但它避免了二义性，如 <code class="docutils literal notranslate"><span class="pre">\g<2>0</span></code>。 <code class="docutils literal notranslate"><span class="pre">\20</span></code> 就会被解释为组20，而不是组2后面跟随一个字符 <code class="docutils literal notranslate"><span class="pre">'0'</span></code>。向后引用 <code class="docutils literal notranslate"><span class="pre">\g<0></span></code> 把 <em>pattern</em> 作为一整个组进行引用。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.1 版更改: </span>增加了可选标记参数。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>不匹配的组合替换为空字符串。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span><em>pattern</em> 中的未知转义（由 <code class="docutils literal notranslate"><span class="pre">'\'</span></code> 和一个 ASCII 字符组成）被视为错误。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span><em>repl</em> 中的未知转义（由 <code class="docutils literal notranslate"><span class="pre">'\'</span></code> 和一个 ASCII 字符组成）被视为错误。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>样式中的空匹配相邻接时会被替换。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.subn">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">subn</code><span class="sig-paren">(</span><em class="sig-param">pattern</em>, <em class="sig-param">repl</em>, <em class="sig-param">string</em>, <em class="sig-param">count=0</em>, <em class="sig-param">flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.subn" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>行为与 <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> 相同，但是返回一个元组 <code class="docutils literal notranslate"><span class="pre">(字符串,</span> <span class="pre">替换次数)</span></code>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.1 版更改: </span>增加了可选标记参数。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>不匹配的组合替换为空字符串。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.escape">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">escape</code><span class="sig-paren">(</span><em class="sig-param">pattern</em><span class="sig-paren">)</span><a class="headerlink" href="#re.escape" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>转义 <em>pattern</em> 中的特殊字符。如果你想对任意可能包含正则表达式元字符的文本字符串进行匹配，它就是有用的。比如</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="s1">'http://www.python.org'</span><span class="p">))</span>
|
||
<span class="go">http://www\.python\.org</span>
|
||
|
||
<span class="gp">>>> </span><span class="n">legal_chars</span> <span class="o">=</span> <span class="n">string</span><span class="o">.</span><span class="n">ascii_lowercase</span> <span class="o">+</span> <span class="n">string</span><span class="o">.</span><span class="n">digits</span> <span class="o">+</span> <span class="s2">"!#$%&'*+-.^_`|~:"</span>
|
||
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="s1">'[</span><span class="si">%s</span><span class="s1">]+'</span> <span class="o">%</span> <span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="n">legal_chars</span><span class="p">))</span>
|
||
<span class="go">[abcdefghijklmnopqrstuvwxyz0123456789!\#\$%\&'\*\+\-\.\^_`\|\~:]+</span>
|
||
|
||
<span class="gp">>>> </span><span class="n">operators</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'+'</span><span class="p">,</span> <span class="s1">'-'</span><span class="p">,</span> <span class="s1">'*'</span><span class="p">,</span> <span class="s1">'/'</span><span class="p">,</span> <span class="s1">'**'</span><span class="p">]</span>
|
||
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="s1">'|'</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">,</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">operators</span><span class="p">,</span> <span class="n">reverse</span><span class="o">=</span><span class="kc">True</span><span class="p">))))</span>
|
||
<span class="go">/|\-|\+|\*\*|\*</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>这个函数不能被用于 <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> 和 <a class="reference internal" href="#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">subn()</span></code></a> 的替换字符串，只有反斜杠应该被转义。 例如:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">digits_re</span> <span class="o">=</span> <span class="sa">r</span><span class="s1">'\d+'</span>
|
||
<span class="gp">>>> </span><span class="n">sample</span> <span class="o">=</span> <span class="s1">'/usr/sbin/sendmail - 0 errors, 12 warnings'</span>
|
||
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="n">digits_re</span><span class="p">,</span> <span class="n">digits_re</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">'</span><span class="se">\\</span><span class="s1">'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'</span><span class="se">\\</span><span class="s1">'</span><span class="p">),</span> <span class="n">sample</span><span class="p">))</span>
|
||
<span class="go">/usr/sbin/sendmail - \d+ errors, \d+ warnings</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.3 版更改: </span><code class="docutils literal notranslate"><span class="pre">'_'</span></code> 不再被转义。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>只有在正则表达式中具有特殊含义的字符才会被转义。 因此， <code class="docutils literal notranslate"><span class="pre">'!'</span></code>, <code class="docutils literal notranslate"><span class="pre">'"'</span></code>, <code class="docutils literal notranslate"><span class="pre">'%'</span></code>, <code class="docutils literal notranslate"><span class="pre">"'"</span></code>, <code class="docutils literal notranslate"><span class="pre">','</span></code>, <code class="docutils literal notranslate"><span class="pre">'/'</span></code>, <code class="docutils literal notranslate"><span class="pre">':'</span></code>, <code class="docutils literal notranslate"><span class="pre">';'</span></code>, <code class="docutils literal notranslate"><span class="pre">'<'</span></code>, <code class="docutils literal notranslate"><span class="pre">'='</span></code>, <code class="docutils literal notranslate"><span class="pre">'>'</span></code>, <code class="docutils literal notranslate"><span class="pre">'@'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">"`"</span></code> 将不再会被转义。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="re.purge">
|
||
<code class="sig-prename descclassname">re.</code><code class="sig-name descname">purge</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#re.purge" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>清除正则表达式的缓存。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="exception">
|
||
<dt id="re.error">
|
||
<em class="property">exception </em><code class="sig-prename descclassname">re.</code><code class="sig-name descname">error</code><span class="sig-paren">(</span><em class="sig-param">msg</em>, <em class="sig-param">pattern=None</em>, <em class="sig-param">pos=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.error" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>当传递给函数的正则表达式不合法（比如括号不匹配），或者在编译或匹配过程中出现其他错误时，会引发异常。所给字符串不匹配所给模式不会引发异常。异常实例有以下附加属性：</p>
|
||
<dl class="attribute">
|
||
<dt id="re.error.msg">
|
||
<code class="sig-name descname">msg</code><a class="headerlink" href="#re.error.msg" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>未格式化的错误消息。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.error.pattern">
|
||
<code class="sig-name descname">pattern</code><a class="headerlink" href="#re.error.pattern" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>正则表达式的模式串。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.error.pos">
|
||
<code class="sig-name descname">pos</code><a class="headerlink" href="#re.error.pos" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>编译失败的 <em>pattern</em> 的位置索引（可以是 <code class="docutils literal notranslate"><span class="pre">None</span></code> ）。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.error.lineno">
|
||
<code class="sig-name descname">lineno</code><a class="headerlink" href="#re.error.lineno" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>对应 <em>pos</em> (可以是 <code class="docutils literal notranslate"><span class="pre">None</span></code>) 的行号。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.error.colno">
|
||
<code class="sig-name descname">colno</code><a class="headerlink" href="#re.error.colno" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>对应 <em>pos</em> (可以是 <code class="docutils literal notranslate"><span class="pre">None</span></code>) 的列号。</p>
|
||
</dd></dl>
|
||
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>增加了额外的属性。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="regular-expression-objects">
|
||
<span id="re-objects"></span><h2>正则表达式对象 （正则对象）<a class="headerlink" href="#regular-expression-objects" title="永久链接至标题">¶</a></h2>
|
||
<p>编译后的正则表达式对象支持以下方法和属性：</p>
|
||
<dl class="method">
|
||
<dt id="re.Pattern.search">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">search</code><span class="sig-paren">(</span><em class="sig-param">string</em><span class="optional">[</span>, <em class="sig-param">pos</em><span class="optional">[</span>, <em class="sig-param">endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.search" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>扫描整个 <em>string</em> 寻找第一个匹配的位置， 并返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a>。如果没有匹配，就返回 <code class="docutils literal notranslate"><span class="pre">None</span></code> ；注意它和零长度匹配是不同的。</p>
|
||
<p>可选的第二个参数 <em>pos</em> 给出了字符串中开始搜索的位置索引；默认为 <code class="docutils literal notranslate"><span class="pre">0</span></code>，它不完全等价于字符串切片； <code class="docutils literal notranslate"><span class="pre">'^'</span></code> 样式字符匹配字符串真正的开头，和换行符后面的第一个字符，但不会匹配索引规定开始的位置。</p>
|
||
<p>可选参数 <em>endpos</em> 限定了字符串搜索的结束；它假定字符串长度到 <em>endpos</em> ， 所以只有从 <code class="docutils literal notranslate"><span class="pre">pos</span></code> 到 <code class="docutils literal notranslate"><span class="pre">endpos</span> <span class="pre">-</span> <span class="pre">1</span></code> 的字符会被匹配。如果 <em>endpos</em> 小于 <em>pos</em>，就不会有匹配产生；另外，如果 <em>rx</em> 是一个编译后的正则对象， <code class="docutils literal notranslate"><span class="pre">rx.search(string,</span> <span class="pre">0,</span> <span class="pre">50)</span></code> 等价于 <code class="docutils literal notranslate"><span class="pre">rx.search(string[:50],</span> <span class="pre">0)</span></code>。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"d"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">)</span> <span class="c1"># Match at index 0</span>
|
||
<span class="go"><re.Match object; span=(0, 1), match='d'></span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># No match; search doesn't include the "d"</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.match">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">match</code><span class="sig-paren">(</span><em class="sig-param">string</em><span class="optional">[</span>, <em class="sig-param">pos</em><span class="optional">[</span>, <em class="sig-param">endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.match" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>如果 <em>string</em> 的 <em>开始位置</em> 能够找到这个正则样式的任意个匹配，就返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a>。如果不匹配，就返回 <code class="docutils literal notranslate"><span class="pre">None</span></code> ；注意它与零长度匹配是不同的。</p>
|
||
<p>可选参数 <em>pos</em> 和 <em>endpos</em> 与 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 含义相同。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"o"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">)</span> <span class="c1"># No match as "o" is not at the start of "dog".</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> <span class="c1"># Match as "o" is the 2nd character of "dog".</span>
|
||
<span class="go"><re.Match object; span=(1, 2), match='o'></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果你想定位匹配在 <em>string</em> 中的位置，使用 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 来替代（另参考 <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a>）。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.fullmatch">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">fullmatch</code><span class="sig-paren">(</span><em class="sig-param">string</em><span class="optional">[</span>, <em class="sig-param">pos</em><span class="optional">[</span>, <em class="sig-param">endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.fullmatch" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>如果整个 <em>string</em> 匹配这个正则表达式，就返回一个相应的 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 。 否则就返回 <code class="docutils literal notranslate"><span class="pre">None</span></code> ； 注意跟零长度匹配是不同的。</p>
|
||
<p>可选参数 <em>pos</em> 和 <em>endpos</em> 与 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 含义相同。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"o[gh]"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">"dog"</span><span class="p">)</span> <span class="c1"># No match as "o" is not at the start of "dog".</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">"ogre"</span><span class="p">)</span> <span class="c1"># No match as not the full string matches.</span>
|
||
<span class="gp">>>> </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">"doggie"</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span> <span class="c1"># Matches within given limits.</span>
|
||
<span class="go"><re.Match object; span=(1, 3), match='og'></span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.4 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.split">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">split</code><span class="sig-paren">(</span><em class="sig-param">string</em>, <em class="sig-param">maxsplit=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.split" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>等价于 <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> 函数，使用了编译后的样式。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.findall">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">findall</code><span class="sig-paren">(</span><em class="sig-param">string</em><span class="optional">[</span>, <em class="sig-param">pos</em><span class="optional">[</span>, <em class="sig-param">endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.findall" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>类似函数 <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> ， 使用了编译后样式，但也可以接收可选参数 <em>pos</em> 和 <em>endpos</em> ，限制搜索范围，就像 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.finditer">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">finditer</code><span class="sig-paren">(</span><em class="sig-param">string</em><span class="optional">[</span>, <em class="sig-param">pos</em><span class="optional">[</span>, <em class="sig-param">endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.finditer" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>类似函数 <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> ， 使用了编译后样式，但也可以接收可选参数 <em>pos</em> 和 <em>endpos</em> ，限制搜索范围，就像 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.sub">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">sub</code><span class="sig-paren">(</span><em class="sig-param">repl</em>, <em class="sig-param">string</em>, <em class="sig-param">count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.sub" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>等价于 <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> 函数，使用了编译后的样式。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Pattern.subn">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">subn</code><span class="sig-paren">(</span><em class="sig-param">repl</em>, <em class="sig-param">string</em>, <em class="sig-param">count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Pattern.subn" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>等价于 <a class="reference internal" href="#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">subn()</span></code></a> 函数，使用了编译后的样式。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Pattern.flags">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">flags</code><a class="headerlink" href="#re.Pattern.flags" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>正则匹配标记。这是可以传递给 <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">compile()</span></code></a> 的参数，任何 <code class="docutils literal notranslate"><span class="pre">(?…)</span></code> 内联标记，隐性标记比如 <code class="xref py py-data docutils literal notranslate"><span class="pre">UNICODE</span></code> 的结合。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Pattern.groups">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">groups</code><a class="headerlink" href="#re.Pattern.groups" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>捕获到的模式串中组的数量。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Pattern.groupindex">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">groupindex</code><a class="headerlink" href="#re.Pattern.groupindex" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>映射由 <code class="docutils literal notranslate"><span class="pre">(?P<id>)</span></code> 定义的命名符号组合和数字组合的字典。如果没有符号组，那字典就是空的。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Pattern.pattern">
|
||
<code class="sig-prename descclassname">Pattern.</code><code class="sig-name descname">pattern</code><a class="headerlink" href="#re.Pattern.pattern" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>编译对象的原始样式字符串。</p>
|
||
</dd></dl>
|
||
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>添加 <a class="reference internal" href="copy.html#copy.copy" title="copy.copy"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy.copy()</span></code></a> 和 <a class="reference internal" href="copy.html#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy.deepcopy()</span></code></a> 函数的支持。编译后的正则表达式对象被认为是原子性的。</p>
|
||
</div>
|
||
</section>
|
||
<section id="match-objects">
|
||
<span id="id2"></span><h2>匹配对象<a class="headerlink" href="#match-objects" title="永久链接至标题">¶</a></h2>
|
||
<p>匹配对象总是有一个布尔值 <code class="docutils literal notranslate"><span class="pre">True</span></code>。如果没有匹配的话 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> 和 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 返回 <code class="docutils literal notranslate"><span class="pre">None</span></code> 所以你可以简单的用 <code class="docutils literal notranslate"><span class="pre">if</span></code> 语句来判断是否匹配</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">match</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
|
||
<span class="k">if</span> <span class="n">match</span><span class="p">:</span>
|
||
<span class="n">process</span><span class="p">(</span><span class="n">match</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>匹配对象支持以下方法和属性：</p>
|
||
<dl class="method">
|
||
<dt id="re.Match.expand">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">expand</code><span class="sig-paren">(</span><em class="sig-param">template</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.expand" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>对 <em>template</em> 进行反斜杠转义替换并且返回，就像 <a class="reference internal" href="#re.Pattern.sub" title="re.Pattern.sub"><code class="xref py py-meth docutils literal notranslate"><span class="pre">sub()</span></code></a> 方法中一样。转义如同 <code class="docutils literal notranslate"><span class="pre">\n</span></code> 被转换成合适的字符，数字引用(<code class="docutils literal notranslate"><span class="pre">\1</span></code>, <code class="docutils literal notranslate"><span class="pre">\2</span></code>)和命名组合(<code class="docutils literal notranslate"><span class="pre">\g<1></span></code>, <code class="docutils literal notranslate"><span class="pre">\g<name></span></code>) 替换为相应组合的内容。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>不匹配的组合替换为空字符串。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.group">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">group</code><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param">group1</em>, <em class="sig-param">...</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.group" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回一个或者多个匹配的子组。如果只有一个参数，结果就是一个字符串，如果有多个参数，结果就是一个元组（每个参数对应一个项），如果没有参数，组1默认到0（整个匹配都被返回）。 如果一个组N 参数值为 0，相应的返回值就是整个匹配字符串；如果它是一个范围 [1..99]，结果就是相应的括号组字符串。如果一个组号是负数，或者大于样式中定义的组数，就引发一个 <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> 异常。如果一个组包含在样式的一部分，并被匹配多次，就返回最后一个匹配。:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w+) (\w+)"</span><span class="p">,</span> <span class="s2">"Isaac Newton, physicist"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="c1"># The entire match</span>
|
||
<span class="go">'Isaac Newton'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="c1"># The first parenthesized subgroup.</span>
|
||
<span class="go">'Isaac'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span> <span class="c1"># The second parenthesized subgroup.</span>
|
||
<span class="go">'Newton'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span> <span class="c1"># Multiple arguments give us a tuple.</span>
|
||
<span class="go">('Isaac', 'Newton')</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果正则表达式使用了 <code class="docutils literal notranslate"><span class="pre">(?P<name>...)</span></code> 语法， <em>groupN</em> 参数就也可能是命名组合的名字。如果一个字符串参数在样式中未定义为组合名，就引发一个 <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> 异常。</p>
|
||
<p>一个相对复杂的例子</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(?P<first_name>\w+) (?P<last_name>\w+)"</span><span class="p">,</span> <span class="s2">"Malcolm Reynolds"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">'first_name'</span><span class="p">)</span>
|
||
<span class="go">'Malcolm'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">'last_name'</span><span class="p">)</span>
|
||
<span class="go">'Reynolds'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>命名组合同样可以通过索引值引用</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="go">'Malcolm'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
|
||
<span class="go">'Reynolds'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果一个组匹配成功多次，就只返回最后一个匹配</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(..)+"</span><span class="p">,</span> <span class="s2">"a1b2c3"</span><span class="p">)</span> <span class="c1"># Matches 3 times.</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="c1"># Returns only the last match.</span>
|
||
<span class="go">'c3'</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.__getitem__">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">__getitem__</code><span class="sig-paren">(</span><em class="sig-param">g</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.__getitem__" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>这个等价于 <code class="docutils literal notranslate"><span class="pre">m.group(g)</span></code>。这允许更方便的引用一个匹配</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w+) (\w+)"</span><span class="p">,</span> <span class="s2">"Isaac Newton, physicist"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="c1"># The entire match</span>
|
||
<span class="go">'Isaac Newton'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="c1"># The first parenthesized subgroup.</span>
|
||
<span class="go">'Isaac'</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="c1"># The second parenthesized subgroup.</span>
|
||
<span class="go">'Newton'</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.6 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.groups">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">groups</code><span class="sig-paren">(</span><em class="sig-param">default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.groups" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回一个元组，包含所有匹配的子组，在样式中出现的从1到任意多的组合。 <em>default</em> 参数用于不参与匹配的情况，默认为 <code class="docutils literal notranslate"><span class="pre">None</span></code>。</p>
|
||
<p>例如：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\d+)\.(\d+)"</span><span class="p">,</span> <span class="s2">"24.1632"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span>
|
||
<span class="go">('24', '1632')</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果我们使小数点可选，那么不是所有的组都会参与到匹配当中。这些组合默认会返回一个 <code class="docutils literal notranslate"><span class="pre">None</span></code> ，除非指定了 <em>default</em> 参数。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\d+)\.?(\d+)?"</span><span class="p">,</span> <span class="s2">"24"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span> <span class="c1"># Second group defaults to None.</span>
|
||
<span class="go">('24', None)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">(</span><span class="s1">'0'</span><span class="p">)</span> <span class="c1"># Now, the second group defaults to '0'.</span>
|
||
<span class="go">('24', '0')</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.groupdict">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">groupdict</code><span class="sig-paren">(</span><em class="sig-param">default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.groupdict" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回一个字典，包含了所有的 <em>命名</em> 子组。key就是组名。 <em>default</em> 参数用于不参与匹配的组合；默认为 <code class="docutils literal notranslate"><span class="pre">None</span></code>。 例如</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(?P<first_name>\w+) (?P<last_name>\w+)"</span><span class="p">,</span> <span class="s2">"Malcolm Reynolds"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">m</span><span class="o">.</span><span class="n">groupdict</span><span class="p">()</span>
|
||
<span class="go">{'first_name': 'Malcolm', 'last_name': 'Reynolds'}</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.start">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">start</code><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param">group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.start" title="永久链接至目标">¶</a></dt>
|
||
<dt id="re.Match.end">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">end</code><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param">group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.end" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回 <em>group</em> 匹配到的字串的开始和结束标号。<em>group</em> 默认为0（意思是整个匹配的子串）。如果 <em>group</em> 存在，但未产生匹配，就返回 <code class="docutils literal notranslate"><span class="pre">-1</span></code> 。对于一个匹配对象 <em>m</em>， 和一个未参与匹配的组 <em>g</em> ，组 <em>g</em> (等价于 <code class="docutils literal notranslate"><span class="pre">m.group(g)</span></code>)产生的匹配是</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">m</span><span class="o">.</span><span class="n">string</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(</span><span class="n">g</span><span class="p">):</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(</span><span class="n">g</span><span class="p">)]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>注意 <code class="docutils literal notranslate"><span class="pre">m.start(group)</span></code> 将会等于 <code class="docutils literal notranslate"><span class="pre">m.end(group)</span></code> ，如果 <em>group</em> 匹配一个空字符串的话。比如，在 <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">=</span> <span class="pre">re.search('b(c?)',</span> <span class="pre">'cba')</span></code> 之后，<code class="docutils literal notranslate"><span class="pre">m.start(0)</span></code> 为 1, <code class="docutils literal notranslate"><span class="pre">m.end(0)</span></code> 为 2, <code class="docutils literal notranslate"><span class="pre">m.start(1)</span></code> 和 <code class="docutils literal notranslate"><span class="pre">m.end(1)</span></code> 都是 2, <code class="docutils literal notranslate"><span class="pre">m.start(2)</span></code> 引发一个 <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> 异常。</p>
|
||
<p>这个例子会从email地址中移除掉 <em>remove_this</em></p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">email</span> <span class="o">=</span> <span class="s2">"tony@tiremove_thisger.net"</span>
|
||
<span class="gp">>>> </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"remove_this"</span><span class="p">,</span> <span class="n">email</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">email</span><span class="p">[:</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">()]</span> <span class="o">+</span> <span class="n">email</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">():]</span>
|
||
<span class="go">'tony@tiger.net'</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="re.Match.span">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">span</code><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param">group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.Match.span" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>对于一个匹配 <em>m</em> ， 返回一个二元组 <code class="docutils literal notranslate"><span class="pre">(m.start(group),</span> <span class="pre">m.end(group))</span></code> 。 注意如果 <em>group</em> 没有在这个匹配中，就返回 <code class="docutils literal notranslate"><span class="pre">(-1,</span> <span class="pre">-1)</span></code> 。<em>group</em> 默认为0，就是整个匹配。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.pos">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">pos</code><a class="headerlink" href="#re.Match.pos" title="永久链接至目标">¶</a></dt>
|
||
<dd><p><em>pos</em> 的值，会传递给 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 或 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> 的方法 a <a class="reference internal" href="#re-objects"><span class="std std-ref">正则对象</span></a> 。这个是正则引擎开始在字符串搜索一个匹配的索引位置。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.endpos">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">endpos</code><a class="headerlink" href="#re.Match.endpos" title="永久链接至目标">¶</a></dt>
|
||
<dd><p><em>endpos</em> 的值，会传递给 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 或 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> 的方法 a <a class="reference internal" href="#re-objects"><span class="std std-ref">正则对象</span></a> 。这个是正则引擎停止在字符串搜索一个匹配的索引位置。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.lastindex">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">lastindex</code><a class="headerlink" href="#re.Match.lastindex" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>捕获组的最后一个匹配的整数索引值，或者 <code class="docutils literal notranslate"><span class="pre">None</span></code> 如果没有匹配产生的话。比如，对于字符串 <code class="docutils literal notranslate"><span class="pre">'ab'</span></code>，表达式 <code class="docutils literal notranslate"><span class="pre">(a)b</span></code>, <code class="docutils literal notranslate"><span class="pre">((a)(b))</span></code>, 和 <code class="docutils literal notranslate"><span class="pre">((ab))</span></code> 将得到 <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">1</span></code> ， 而 <code class="docutils literal notranslate"><span class="pre">(a)(b)</span></code> 会得到 <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">2</span></code> 。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.lastgroup">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">lastgroup</code><a class="headerlink" href="#re.Match.lastgroup" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>最后一个匹配的命名组名字，或者 <code class="docutils literal notranslate"><span class="pre">None</span></code> 如果没有产生匹配的话。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.re">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">re</code><a class="headerlink" href="#re.Match.re" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回产生这个实例的 <a class="reference internal" href="#re-objects"><span class="std std-ref">正则对象</span></a> ， 这个实例是由 正则对象的 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> 或 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 方法产生的。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="attribute">
|
||
<dt id="re.Match.string">
|
||
<code class="sig-prename descclassname">Match.</code><code class="sig-name descname">string</code><a class="headerlink" href="#re.Match.string" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>传递到 <a class="reference internal" href="#re.Pattern.match" title="re.Pattern.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> 或 <a class="reference internal" href="#re.Pattern.search" title="re.Pattern.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> 的字符串。</p>
|
||
</dd></dl>
|
||
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>添加了对 <a class="reference internal" href="copy.html#copy.copy" title="copy.copy"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy.copy()</span></code></a> 和 <a class="reference internal" href="copy.html#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy.deepcopy()</span></code></a> 的支持。匹配对象被看作是原子性的。</p>
|
||
</div>
|
||
</section>
|
||
<section id="regular-expression-examples">
|
||
<span id="re-examples"></span><h2>正则表达式例子<a class="headerlink" href="#regular-expression-examples" title="永久链接至标题">¶</a></h2>
|
||
<section id="checking-for-a-pair">
|
||
<h3>检查对子<a class="headerlink" href="#checking-for-a-pair" title="永久链接至标题">¶</a></h3>
|
||
<p>在这个例子里，我们使用以下辅助函数来更好地显示匹配对象:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">displaymatch</span><span class="p">(</span><span class="n">match</span><span class="p">):</span>
|
||
<span class="k">if</span> <span class="n">match</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
|
||
<span class="k">return</span> <span class="kc">None</span>
|
||
<span class="k">return</span> <span class="s1">'<Match: </span><span class="si">%r</span><span class="s1">, groups=</span><span class="si">%r</span><span class="s1">>'</span> <span class="o">%</span> <span class="p">(</span><span class="n">match</span><span class="o">.</span><span class="n">group</span><span class="p">(),</span> <span class="n">match</span><span class="o">.</span><span class="n">groups</span><span class="p">())</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>假设你在写一个扑克程序，一个玩家的一手牌为五个字符的串，每个字符表示一张牌，"a" 就是 A, "k" K， "q" Q, "j" J, "t" 为 10, "2" 到 "9" 表示2 到 9。</p>
|
||
<p>要看给定的字符串是否有效，我们可以按照以下步骤</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">"^[a2-9tjqk]</span><span class="si">{5}</span><span class="s2">$"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt5q"</span><span class="p">))</span> <span class="c1"># Valid.</span>
|
||
<span class="go">"<Match: 'akt5q', groups=()>"</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt5e"</span><span class="p">))</span> <span class="c1"># Invalid.</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"akt"</span><span class="p">))</span> <span class="c1"># Invalid.</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"727ak"</span><span class="p">))</span> <span class="c1"># Valid.</span>
|
||
<span class="go">"<Match: '727ak', groups=()>"</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>最后一手牌，<code class="docutils literal notranslate"><span class="pre">"727ak"</span></code> ，包含了一个对子，或者两张同样数值的牌。要用正则表达式匹配它，应该使用向后引用如下</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pair</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">".*(.).*\1"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"717ak"</span><span class="p">))</span> <span class="c1"># Pair of 7s.</span>
|
||
<span class="go">"<Match: '717', groups=('7',)>"</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"718ak"</span><span class="p">))</span> <span class="c1"># No pairs.</span>
|
||
<span class="gp">>>> </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"354aa"</span><span class="p">))</span> <span class="c1"># Pair of aces.</span>
|
||
<span class="go">"<Match: '354aa', groups=('a',)>"</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>要找出对子由什么牌组成，开发者可以按照下面的方式来使用匹配对象的 <a class="reference internal" href="#re.Match.group" title="re.Match.group"><code class="xref py py-meth docutils literal notranslate"><span class="pre">group()</span></code></a> 方法:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">pair</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">".*(.).*\1"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"717ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="go">'7'</span>
|
||
|
||
<span class="go"># Error because re.match() returns None, which doesn't have a group() method:</span>
|
||
<span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"718ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="gt">Traceback (most recent call last):</span>
|
||
File <span class="nb">"<pyshell#23>"</span>, line <span class="m">1</span>, in <span class="n"><module></span>
|
||
<span class="w"> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">".*(.).*\1"</span><span class="p">,</span> <span class="s2">"718ak"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="gr">AttributeError</span>: <span class="n">'NoneType' object has no attribute 'group'</span>
|
||
|
||
<span class="gp">>>> </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"354aa"</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
|
||
<span class="go">'a'</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="simulating-scanf">
|
||
<h3>模拟 scanf()<a class="headerlink" href="#simulating-scanf" title="永久链接至标题">¶</a></h3>
|
||
<p id="index-38">Python 目前没有一个类似c函数 <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> 的替代品。正则表达式通常比 <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> 格式字符串要更强大一些，但也带来更多复杂性。下面的表格提供了 <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> 格式符和正则表达式大致相同的映射。</p>
|
||
<table class="docutils align-default">
|
||
<colgroup>
|
||
<col style="width: 42%" />
|
||
<col style="width: 58%" />
|
||
</colgroup>
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p><code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> 格式符</p></th>
|
||
<th class="head"><p>正则表达式</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">%c</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">.</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">%5c</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">.{5}</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">%d</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">[-+]?\d+</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">%e</span></code>, <code class="docutils literal notranslate"><span class="pre">%E</span></code>, <code class="docutils literal notranslate"><span class="pre">%f</span></code>, <code class="docutils literal notranslate"><span class="pre">%g</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">%i</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">%o</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">[-+]?[0-7]+</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">%s</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">\S+</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">%u</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">\d+</span></code></p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">%x</span></code>, <code class="docutils literal notranslate"><span class="pre">%X</span></code></p></td>
|
||
<td><p><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX])?[\dA-Fa-f]+</span></code></p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p>从文件名和数字提取字符串</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">sbin</span><span class="o">/</span><span class="n">sendmail</span> <span class="o">-</span> <span class="mi">0</span> <span class="n">errors</span><span class="p">,</span> <span class="mi">4</span> <span class="n">warnings</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>你可以使用 <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> 格式化</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o">%</span><span class="n">s</span> <span class="o">-</span> <span class="o">%</span><span class="n">d</span> <span class="n">errors</span><span class="p">,</span> <span class="o">%</span><span class="n">d</span> <span class="n">warnings</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>等价的正则表达式是：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">(</span>\<span class="n">S</span><span class="o">+</span><span class="p">)</span> <span class="o">-</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">errors</span><span class="p">,</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">warnings</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="search-vs-match">
|
||
<span id="id3"></span><h3>search() vs. match()<a class="headerlink" href="#search-vs-match" title="永久链接至标题">¶</a></h3>
|
||
<p>Python 提供了两种不同的操作：基于 <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> 检查字符串开头，或者 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.search()</span></code></a> 检查字符串的任意位置（默认Perl中的行为）。</p>
|
||
<p>例如：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># Match</span>
|
||
<span class="go"><re.Match object; span=(2, 3), match='c'></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>在 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 中，可以用 <code class="docutils literal notranslate"><span class="pre">'^'</span></code> 作为开始来限制匹配到字符串的首位</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"^c"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># No match</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">"^a"</span><span class="p">,</span> <span class="s2">"abcdef"</span><span class="p">)</span> <span class="c1"># Match</span>
|
||
<span class="go"><re.Match object; span=(0, 1), match='a'></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>注意 <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> 多行模式中函数 <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> 只匹配字符串的开始，但使用 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 和以 <code class="docutils literal notranslate"><span class="pre">'^'</span></code> 开始的正则表达式会匹配每行的开始</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">'X'</span><span class="p">,</span> <span class="s1">'A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X'</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span> <span class="c1"># No match</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">'^X'</span><span class="p">,</span> <span class="s1">'A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X'</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span> <span class="c1"># Match</span>
|
||
<span class="go"><re.Match object; span=(4, 5), match='X'></span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="making-a-phonebook">
|
||
<h3>制作一个电话本<a class="headerlink" href="#making-a-phonebook" title="永久链接至标题">¶</a></h3>
|
||
<p><a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> 将字符串用参数传递的样式分隔开。这个方法对于转换文本数据到易读而且容易修改的数据结构，是很有用的，如下面的例子证明。</p>
|
||
<p>首先，这里是输入。 它通常来自一个文件，这里我们使用三重引号字符串语法</p>
|
||
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"""Ross McFluff: 834.345.1254 155 Elm Street</span>
|
||
<span class="gp">...</span>
|
||
<span class="gp">... </span><span class="s2">Ronald Heathmore: 892.345.3428 436 Finley Avenue</span>
|
||
<span class="gp">... </span><span class="s2">Frank Burger: 925.541.7625 662 South Dogwood Way</span>
|
||
<span class="gp">...</span>
|
||
<span class="gp">...</span>
|
||
<span class="gp">... </span><span class="s2">Heather Albrecht: 548.326.4584 919 Park Place"""</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>条目用一个或者多个换行符分开。现在我们将字符串转换为一个列表，每个非空行都有一个条目:</p>
|
||
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">entries</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">"</span><span class="se">\n</span><span class="s2">+"</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">entries</span>
|
||
<span class="go">['Ross McFluff: 834.345.1254 155 Elm Street',</span>
|
||
<span class="go">'Ronald Heathmore: 892.345.3428 436 Finley Avenue',</span>
|
||
<span class="go">'Frank Burger: 925.541.7625 662 South Dogwood Way',</span>
|
||
<span class="go">'Heather Albrecht: 548.326.4584 919 Park Place']</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>最终，将每个条目分割为一个由名字、姓氏、电话号码和地址组成的列表。我们为 <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> 使用了 <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> 形参，因为地址中包含有被我们作为分割模式的空格符:</p>
|
||
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">":? "</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
|
||
<span class="go">[['Ross', 'McFluff', '834.345.1254', '155 Elm Street'],</span>
|
||
<span class="go">['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'],</span>
|
||
<span class="go">['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'],</span>
|
||
<span class="go">['Heather', 'Albrecht', '548.326.4584', '919 Park Place']]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p><code class="docutils literal notranslate"><span class="pre">:?</span></code> 样式匹配姓后面的冒号，因此它不出现在结果列表中。如果 <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> 设置为 <code class="docutils literal notranslate"><span class="pre">4</span></code> ，我们还可以从地址中获取到房间号:</p>
|
||
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">":? "</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
|
||
<span class="go">[['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'],</span>
|
||
<span class="go">['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'],</span>
|
||
<span class="go">['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'],</span>
|
||
<span class="go">['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']]</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="text-munging">
|
||
<h3>文字整理<a class="headerlink" href="#text-munging" title="永久链接至标题">¶</a></h3>
|
||
<p><a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> 替换字符串中出现的样式的每一个实例。这个例子证明了使用 <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> 来整理文字，或者随机化每个字符的位置，除了首位和末尾字符</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">repl</span><span class="p">(</span><span class="n">m</span><span class="p">):</span>
|
||
<span class="gp">... </span> <span class="n">inner_word</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
|
||
<span class="gp">... </span> <span class="n">random</span><span class="o">.</span><span class="n">shuffle</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span>
|
||
<span class="gp">... </span> <span class="k">return</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="s2">""</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span> <span class="o">+</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Professor Abdolmalek, please report your absences promptly."</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w)(\w+)(\w)"</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
|
||
<span class="go">'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.'</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">"(\w)(\w+)(\w)"</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
|
||
<span class="go">'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.'</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="finding-all-adverbs">
|
||
<h3>查找所有副词<a class="headerlink" href="#finding-all-adverbs" title="永久链接至标题">¶</a></h3>
|
||
<p><a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> 匹配样式 <em>所有</em> 的出现，不仅是像 <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> 中的第一个匹配。比如，如果一个作者希望找到文字中的所有副词，他可能会按照以下方法用 <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a></p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"He was carefully disguised but captured quickly by police."</span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\w+ly"</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
|
||
<span class="go">['carefully', 'quickly']</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="finding-all-adverbs-and-their-positions">
|
||
<h3>查找所有的副词及其位置<a class="headerlink" href="#finding-all-adverbs-and-their-positions" title="永久链接至标题">¶</a></h3>
|
||
<p>如果需要匹配样式的更多信息， <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> 可以起到作用，它提供了 <a class="reference internal" href="#match-objects"><span class="std std-ref">匹配对象</span></a> 作为返回值，而不是字符串。继续上面的例子，如果一个作者希望找到所有副词和它的位置，可以按照下面方法使用 <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a></p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">text</span> <span class="o">=</span> <span class="s2">"He was carefully disguised but captured quickly by police."</span>
|
||
<span class="gp">>>> </span><span class="k">for</span> <span class="n">m</span> <span class="ow">in</span> <span class="n">re</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\w+ly"</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
|
||
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%02d</span><span class="s1">-</span><span class="si">%02d</span><span class="s1">: </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)))</span>
|
||
<span class="go">07-16: carefully</span>
|
||
<span class="go">40-47: quickly</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="raw-string-notation">
|
||
<h3>原始字符串标记<a class="headerlink" href="#raw-string-notation" title="永久链接至标题">¶</a></h3>
|
||
<p>原始字符串记法 (<code class="docutils literal notranslate"><span class="pre">r"text"</span></code>) 保持正则表达式正常。否则，每个正则式里的反斜杠(<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) 都必须前缀一个反斜杠来转义。比如，下面两行代码功能就是完全一致的</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"\W(.)\1\W"</span><span class="p">,</span> <span class="s2">" ff "</span><span class="p">)</span>
|
||
<span class="go"><re.Match object; span=(0, 4), match=' ff '></span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"</span><span class="se">\\</span><span class="s2">W(.)</span><span class="se">\\</span><span class="s2">1</span><span class="se">\\</span><span class="s2">W"</span><span class="p">,</span> <span class="s2">" ff "</span><span class="p">)</span>
|
||
<span class="go"><re.Match object; span=(0, 4), match=' ff '></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>当需要匹配一个字符反斜杠，它必须在正则表达式中转义。在原始字符串记法，就是 <code class="docutils literal notranslate"><span class="pre">r"\\"</span></code>。否则就必须用 <code class="docutils literal notranslate"><span class="pre">"\\\\"</span></code>，来表示同样的意思</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">,</span> <span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">)</span>
|
||
<span class="go"><re.Match object; span=(0, 1), match='\\'></span>
|
||
<span class="gp">>>> </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">"</span><span class="se">\\\\</span><span class="s2">"</span><span class="p">,</span> <span class="sa">r</span><span class="s2">"</span><span class="se">\\</span><span class="s2">"</span><span class="p">)</span>
|
||
<span class="go"><re.Match object; span=(0, 1), match='\\'></span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="writing-a-tokenizer">
|
||
<h3>写一个词法分析器<a class="headerlink" href="#writing-a-tokenizer" title="永久链接至标题">¶</a></h3>
|
||
<p>一个 <a class="reference external" href="https://en.wikipedia.org/wiki/Lexical_analysis">词法器或词法分析器</a> 分析字符串，并分类成目录组。 这是写一个编译器或解释器的第一步。</p>
|
||
<p>文字目录是由正则表达式指定的。这个技术是通过将这些样式合并为一个主正则式，并且循环匹配来实现的</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">NamedTuple</span>
|
||
<span class="kn">import</span> <span class="nn">re</span>
|
||
|
||
<span class="k">class</span> <span class="nc">Token</span><span class="p">(</span><span class="n">NamedTuple</span><span class="p">):</span>
|
||
<span class="nb">type</span><span class="p">:</span> <span class="nb">str</span>
|
||
<span class="n">value</span><span class="p">:</span> <span class="nb">str</span>
|
||
<span class="n">line</span><span class="p">:</span> <span class="nb">int</span>
|
||
<span class="n">column</span><span class="p">:</span> <span class="nb">int</span>
|
||
|
||
<span class="k">def</span> <span class="nf">tokenize</span><span class="p">(</span><span class="n">code</span><span class="p">):</span>
|
||
<span class="n">keywords</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'IF'</span><span class="p">,</span> <span class="s1">'THEN'</span><span class="p">,</span> <span class="s1">'ENDIF'</span><span class="p">,</span> <span class="s1">'FOR'</span><span class="p">,</span> <span class="s1">'NEXT'</span><span class="p">,</span> <span class="s1">'GOSUB'</span><span class="p">,</span> <span class="s1">'RETURN'</span><span class="p">}</span>
|
||
<span class="n">token_specification</span> <span class="o">=</span> <span class="p">[</span>
|
||
<span class="p">(</span><span class="s1">'NUMBER'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'\d+(\.\d*)?'</span><span class="p">),</span> <span class="c1"># Integer or decimal number</span>
|
||
<span class="p">(</span><span class="s1">'ASSIGN'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">':='</span><span class="p">),</span> <span class="c1"># Assignment operator</span>
|
||
<span class="p">(</span><span class="s1">'END'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">';'</span><span class="p">),</span> <span class="c1"># Statement terminator</span>
|
||
<span class="p">(</span><span class="s1">'ID'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'[A-Za-z]+'</span><span class="p">),</span> <span class="c1"># Identifiers</span>
|
||
<span class="p">(</span><span class="s1">'OP'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'[+\-*/]'</span><span class="p">),</span> <span class="c1"># Arithmetic operators</span>
|
||
<span class="p">(</span><span class="s1">'NEWLINE'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'\n'</span><span class="p">),</span> <span class="c1"># Line endings</span>
|
||
<span class="p">(</span><span class="s1">'SKIP'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'[ \t]+'</span><span class="p">),</span> <span class="c1"># Skip over spaces and tabs</span>
|
||
<span class="p">(</span><span class="s1">'MISMATCH'</span><span class="p">,</span> <span class="sa">r</span><span class="s1">'.'</span><span class="p">),</span> <span class="c1"># Any other character</span>
|
||
<span class="p">]</span>
|
||
<span class="n">tok_regex</span> <span class="o">=</span> <span class="s1">'|'</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="s1">'(?P<</span><span class="si">%s</span><span class="s1">></span><span class="si">%s</span><span class="s1">)'</span> <span class="o">%</span> <span class="n">pair</span> <span class="k">for</span> <span class="n">pair</span> <span class="ow">in</span> <span class="n">token_specification</span><span class="p">)</span>
|
||
<span class="n">line_num</span> <span class="o">=</span> <span class="mi">1</span>
|
||
<span class="n">line_start</span> <span class="o">=</span> <span class="mi">0</span>
|
||
<span class="k">for</span> <span class="n">mo</span> <span class="ow">in</span> <span class="n">re</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="n">tok_regex</span><span class="p">,</span> <span class="n">code</span><span class="p">):</span>
|
||
<span class="n">kind</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">lastgroup</span>
|
||
<span class="n">value</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">group</span><span class="p">()</span>
|
||
<span class="n">column</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">start</span><span class="p">()</span> <span class="o">-</span> <span class="n">line_start</span>
|
||
<span class="k">if</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">'NUMBER'</span><span class="p">:</span>
|
||
<span class="n">value</span> <span class="o">=</span> <span class="nb">float</span><span class="p">(</span><span class="n">value</span><span class="p">)</span> <span class="k">if</span> <span class="s1">'.'</span> <span class="ow">in</span> <span class="n">value</span> <span class="k">else</span> <span class="nb">int</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
|
||
<span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">'ID'</span> <span class="ow">and</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">keywords</span><span class="p">:</span>
|
||
<span class="n">kind</span> <span class="o">=</span> <span class="n">value</span>
|
||
<span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">'NEWLINE'</span><span class="p">:</span>
|
||
<span class="n">line_start</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">end</span><span class="p">()</span>
|
||
<span class="n">line_num</span> <span class="o">+=</span> <span class="mi">1</span>
|
||
<span class="k">continue</span>
|
||
<span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">'SKIP'</span><span class="p">:</span>
|
||
<span class="k">continue</span>
|
||
<span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">'MISMATCH'</span><span class="p">:</span>
|
||
<span class="k">raise</span> <span class="ne">RuntimeError</span><span class="p">(</span><span class="sa">f</span><span class="s1">'</span><span class="si">{</span><span class="n">value</span><span class="si">!r}</span><span class="s1"> unexpected on line </span><span class="si">{</span><span class="n">line_num</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
|
||
<span class="k">yield</span> <span class="n">Token</span><span class="p">(</span><span class="n">kind</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">line_num</span><span class="p">,</span> <span class="n">column</span><span class="p">)</span>
|
||
|
||
<span class="n">statements</span> <span class="o">=</span> <span class="s1">'''</span>
|
||
<span class="s1"> IF quantity THEN</span>
|
||
<span class="s1"> total := total + price * quantity;</span>
|
||
<span class="s1"> tax := price * 0.05;</span>
|
||
<span class="s1"> ENDIF;</span>
|
||
<span class="s1">'''</span>
|
||
|
||
<span class="k">for</span> <span class="n">token</span> <span class="ow">in</span> <span class="n">tokenize</span><span class="p">(</span><span class="n">statements</span><span class="p">):</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="n">token</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>该词法器产生以下的输出</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'IF'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'IF'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'quantity'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">7</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'THEN'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'THEN'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">16</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'total'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ASSIGN'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">':='</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">14</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'total'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">17</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'OP'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'+'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">23</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'price'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">25</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'OP'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'*'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">31</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'quantity'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">33</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'END'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">';'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">41</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'tax'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ASSIGN'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">':='</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">12</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ID'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'price'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">15</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'OP'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'*'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">21</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'NUMBER'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="mf">0.05</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">23</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'END'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">';'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">27</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'ENDIF'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">'ENDIF'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span>
|
||
<span class="n">Token</span><span class="p">(</span><span class="nb">type</span><span class="o">=</span><span class="s1">'END'</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">';'</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">9</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<dl class="citation">
|
||
<dt class="label" id="frie09"><span class="brackets"><a class="fn-backref" href="#id1">Frie09</a></span></dt>
|
||
<dd><p>Friedl, Jeffrey. Mastering Regular Expressions. 3rd ed., O'Reilly Media, 2009. 该书的第三版不再包含 Python，但第一版极详细地覆盖了正则表达式模式串的编写。</p>
|
||
</dd>
|
||
</dl>
|
||
</section>
|
||
</section>
|
||
</section>
|
||
|
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|
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|
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|
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|
||
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|
||
<div class="sphinxsidebarwrapper">
|
||
<h3><a href="../contents.html">目录</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code> --- 正则表达式操作</a><ul>
|
||
<li><a class="reference internal" href="#regular-expression-syntax">正则表达式语法</a></li>
|
||
<li><a class="reference internal" href="#module-contents">模块内容</a></li>
|
||
<li><a class="reference internal" href="#regular-expression-objects">正则表达式对象 （正则对象）</a></li>
|
||
<li><a class="reference internal" href="#match-objects">匹配对象</a></li>
|
||
<li><a class="reference internal" href="#regular-expression-examples">正则表达式例子</a><ul>
|
||
<li><a class="reference internal" href="#checking-for-a-pair">检查对子</a></li>
|
||
<li><a class="reference internal" href="#simulating-scanf">模拟 scanf()</a></li>
|
||
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|
||
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|
||
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|
||
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|
||
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|
||
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|
||
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|
||
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|
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最后更新于 12月 09, 2024.
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||
<a href="https://docs.python.org/3/bugs.html">Found a bug</a>?
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