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<li><a class="reference internal" href="#">2. 词法分析</a><ul>
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<section id="lexical-analysis">
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<span id="lexical"></span><h1><span class="section-number">2. </span>词法分析<a class="headerlink" href="#lexical-analysis" title="永久链接至标题">¶</a></h1>
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<p id="index-0">Python 程序由 <em>解析器</em> 读取，输入解析器的是 <em>词法分析器</em> 生成的 <em>形符</em> 流。本章介绍词法分析器怎样把文件拆成形符。</p>
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<p>Python 将读取的程序文本转为 Unicode 代码点；编码声明用于指定源文件的编码，默认为 UTF-8，详见 <span class="target" id="index-37"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3120"><strong>PEP 3120</strong></a>。源文件不能解码时，触发 <a class="reference internal" href="../library/exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a>。</p>
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<section id="line-structure">
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<span id="id1"></span><h2><span class="section-number">2.1. </span>行结构<a class="headerlink" href="#line-structure" title="永久链接至标题">¶</a></h2>
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<p id="index-2">Python 程序可以拆分为多个 <em>逻辑行</em>。</p>
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<section id="logical-lines">
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<span id="id2"></span><h3><span class="section-number">2.1.1. </span>逻辑行<a class="headerlink" href="#logical-lines" title="永久链接至标题">¶</a></h3>
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<p id="index-3">NEWLINE 形符表示结束逻辑行。语句不能超出逻辑行的边界，除非句法支持 NEWLINE （例如，复合语句中的多行子语句）。根据显式或隐式 <em>行拼接</em> 规则，一个或多个 <em>物理行</em> 可组成逻辑行。</p>
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</section>
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<section id="physical-lines">
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<span id="id3"></span><h3><span class="section-number">2.1.2. </span>物理行<a class="headerlink" href="#physical-lines" title="永久链接至标题">¶</a></h3>
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<p>物理行是一序列字符，由行尾序列终止。源文件和字符串可使用任意标准平台行终止序列 - Unix ASCII 字符 LF （换行）、 Windows ASCII 字符序列 CR LF （回车换行）、或老式 Macintosh ASCII 字符 CR （回车）。不管在哪个平台，这些形式均可等价使用。输入结束也可以用作最终物理行的隐式终止符。</p>
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<p>嵌入 Python 时，传入 Python API 的源码字符串应使用 C 标准惯例换行符（<code class="docutils literal notranslate"><span class="pre">\n</span></code>，代表 ASCII 字符 LF， 行终止符）。</p>
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</section>
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<section id="comments">
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<span id="id4"></span><h3><span class="section-number">2.1.3. </span>注释<a class="headerlink" href="#comments" title="永久链接至标题">¶</a></h3>
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<p id="index-4">注释以井号 （<code class="docutils literal notranslate"><span class="pre">#</span></code>） 开头，在物理行末尾截止。注意，井号不是字符串字面值。除非应用隐式行拼接规则，否则，注释代表逻辑行结束。句法不解析注释。</p>
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</section>
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<section id="encoding-declarations">
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<span id="encodings"></span><h3><span class="section-number">2.1.4. </span>编码声明<a class="headerlink" href="#encoding-declarations" title="永久链接至标题">¶</a></h3>
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<p id="index-5">Python 脚本第一或第二行的注释匹配正则表达式 <code class="docutils literal notranslate"><span class="pre">coding[=:]\s*([-\w.]+)</span></code> 时，该注释会被当作编码声明；这个表达式的第一组指定了源码文件的编码。编码声明必须独占一行，在第二行时，则第一行必须也是注释。编码表达式的形式如下：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># -*- coding: <encoding-name> -*-</span>
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</pre></div>
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</div>
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<p>这也是 GNU Emacs 认可的形式，此外，还支持如下形式：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># vim:fileencoding=<encoding-name></span>
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</pre></div>
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</div>
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<p>这是 Bram Moolenaar 的 VIM 认可的形式。</p>
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<p>没有编码声明时，默认编码为 UTF-8。此外，如果文件的首字节为 UTF-8 字节顺序标志（<code class="docutils literal notranslate"><span class="pre">b'\xef\xbb\xbf'</span></code>），文件编码也声明为 UTF-8（这是 Microsoft 的 <strong class="program">notepad</strong> 等软件支持的形式）。</p>
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<p>编码声明指定的编码名称必须是 Python 所认可的编码。所有词法分析将使用此编码，包括语义字符串、注释和标识符。</p>
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</section>
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<section id="explicit-line-joining">
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<span id="explicit-joining"></span><h3><span class="section-number">2.1.5. </span>显式拼接行<a class="headerlink" href="#explicit-line-joining" title="永久链接至标题">¶</a></h3>
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<p id="index-6">两个及两个以上的物理行可用反斜杠（<code class="docutils literal notranslate"><span class="pre">\</span></code>）拼接为一个逻辑行，规则如下：以不在字符串或注释内的反斜杠结尾时，物理行将与下一行拼接成一个逻辑行，并删除反斜杠及其后的换行符。例如：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="mi">1900</span> <span class="o"><</span> <span class="n">year</span> <span class="o"><</span> <span class="mi">2100</span> <span class="ow">and</span> <span class="mi">1</span> <span class="o"><=</span> <span class="n">month</span> <span class="o"><=</span> <span class="mi">12</span> \
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<span class="ow">and</span> <span class="mi">1</span> <span class="o"><=</span> <span class="n">day</span> <span class="o"><=</span> <span class="mi">31</span> <span class="ow">and</span> <span class="mi">0</span> <span class="o"><=</span> <span class="n">hour</span> <span class="o"><</span> <span class="mi">24</span> \
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<span class="ow">and</span> <span class="mi">0</span> <span class="o"><=</span> <span class="n">minute</span> <span class="o"><</span> <span class="mi">60</span> <span class="ow">and</span> <span class="mi">0</span> <span class="o"><=</span> <span class="n">second</span> <span class="o"><</span> <span class="mi">60</span><span class="p">:</span> <span class="c1"># Looks like a valid date</span>
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<span class="k">return</span> <span class="mi">1</span>
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</pre></div>
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</div>
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<p>以反斜杠结尾的行，不能加注释；反斜杠也不能拼接注释。除字符串字面值外，反斜杠不能拼接形符（如，除字符串字面值外，不能用反斜杠把形符切分至两个物理行）。反斜杠只能在代码的字符串字面值里，在其他任何位置都是非法的。</p>
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</section>
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<section id="implicit-line-joining">
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<span id="implicit-joining"></span><h3><span class="section-number">2.1.6. </span>隐式拼接行<a class="headerlink" href="#implicit-line-joining" title="永久链接至标题">¶</a></h3>
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<p>圆括号、方括号、花括号内的表达式可以分成多个物理行，不必使用反斜杠。例如：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">month_names</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'Januari'</span><span class="p">,</span> <span class="s1">'Februari'</span><span class="p">,</span> <span class="s1">'Maart'</span><span class="p">,</span> <span class="c1"># These are the</span>
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<span class="s1">'April'</span><span class="p">,</span> <span class="s1">'Mei'</span><span class="p">,</span> <span class="s1">'Juni'</span><span class="p">,</span> <span class="c1"># Dutch names</span>
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<span class="s1">'Juli'</span><span class="p">,</span> <span class="s1">'Augustus'</span><span class="p">,</span> <span class="s1">'September'</span><span class="p">,</span> <span class="c1"># for the months</span>
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<span class="s1">'Oktober'</span><span class="p">,</span> <span class="s1">'November'</span><span class="p">,</span> <span class="s1">'December'</span><span class="p">]</span> <span class="c1"># of the year</span>
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</pre></div>
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</div>
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<p>隐式行拼接可含注释；后续行的缩进并不重要；还支持空的后续行。隐式拼接行之间没有 NEWLINE 形符。三引号字符串支持隐式拼接行（见下文），但不支持注释。</p>
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</section>
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<section id="blank-lines">
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<span id="id5"></span><h3><span class="section-number">2.1.7. </span>空白行<a class="headerlink" href="#blank-lines" title="永久链接至标题">¶</a></h3>
|
||
<p id="index-7">只包含空格符、制表符、换页符、注释的逻辑行会被忽略（即不生成 NEWLINE 形符）。交互模式输入语句时，空白行的处理方式可能因读取 - 求值 - 打印循环（REPL）的具体实现方式而不同。标准交互模式解释器中，完全空白的逻辑行（即连空格或注释都没有）将结束多行复合语句。</p>
|
||
</section>
|
||
<section id="indentation">
|
||
<span id="id6"></span><h3><span class="section-number">2.1.8. </span>缩进<a class="headerlink" href="#indentation" title="永久链接至标题">¶</a></h3>
|
||
<p id="index-8">逻辑行开头的空白符（空格符和制表符）用于计算该行的缩进层级，决定语句组块。</p>
|
||
<p>制表符（从左至右）被替换为一至八个空格，缩进空格的总数是八的倍数（与 Unix 的规则保持一致）。首个非空字符前的空格数决定了该行的缩进层次。缩进不能用反斜杠进行多行拼接；首个反斜杠之前的空白符决定了缩进的层次。</p>
|
||
<p>源文件混用制表符和空格符缩进时，因空格数量与制表符相关，由此产生的不一致将导致不能正常识别缩进层次，从而触发 <a class="reference internal" href="../library/exceptions.html#TabError" title="TabError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TabError</span></code></a>。</p>
|
||
<p><strong>跨平台兼容性说明：</strong> 鉴于非 UNIX 平台文本编辑器本身的特性，请勿在源文件中混用制表符和空格符。另外也请注意，不同平台有可能会显式限制最大缩进层级。</p>
|
||
<p>行首含换页符时，缩进计算将忽略该换页符。换页符在行首空白符内其他位置的效果未定义（例如，可能导致空格计数重置为零）。</p>
|
||
<p id="index-9">连续行的缩进层级以堆栈形式生成 INDENT 和 DEDENT 形符，说明如下。</p>
|
||
<p>读取文件第一行前，先向栈推入一个零值，该零值不会被移除。推入栈的层级值从底至顶持续增加。每个逻辑行开头的行缩进层级将与栈顶行比较。如果相等，则不做处理。如果新行层级较高，则会被推入栈顶，并生成一个 INDENT 形符。如果新行层级较低，则 <em>应当</em> 是栈中的层级数值之一；栈中高于该层级的所有数值都将被移除，每移除一级数值生成一个 DEDENT 形符。文件末尾，栈中剩余的每个大于零的数值生成一个 DEDENT 形符。</p>
|
||
<p>下面的 Python 代码缩进示例虽然正确，但含混不清：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">perm</span><span class="p">(</span><span class="n">l</span><span class="p">):</span>
|
||
<span class="c1"># Compute the list of all permutations of l</span>
|
||
<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">l</span><span class="p">)</span> <span class="o"><=</span> <span class="mi">1</span><span class="p">:</span>
|
||
<span class="k">return</span> <span class="p">[</span><span class="n">l</span><span class="p">]</span>
|
||
<span class="n">r</span> <span class="o">=</span> <span class="p">[]</span>
|
||
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">l</span><span class="p">)):</span>
|
||
<span class="n">s</span> <span class="o">=</span> <span class="n">l</span><span class="p">[:</span><span class="n">i</span><span class="p">]</span> <span class="o">+</span> <span class="n">l</span><span class="p">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">:]</span>
|
||
<span class="n">p</span> <span class="o">=</span> <span class="n">perm</span><span class="p">(</span><span class="n">s</span><span class="p">)</span>
|
||
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">p</span><span class="p">:</span>
|
||
<span class="n">r</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">l</span><span class="p">[</span><span class="n">i</span><span class="p">:</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">]</span> <span class="o">+</span> <span class="n">x</span><span class="p">)</span>
|
||
<span class="k">return</span> <span class="n">r</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>下例展示了多种缩进错误：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span> <span class="k">def</span> <span class="nf">perm</span><span class="p">(</span><span class="n">l</span><span class="p">):</span> <span class="c1"># error: first line indented</span>
|
||
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">l</span><span class="p">)):</span> <span class="c1"># error: not indented</span>
|
||
<span class="n">s</span> <span class="o">=</span> <span class="n">l</span><span class="p">[:</span><span class="n">i</span><span class="p">]</span> <span class="o">+</span> <span class="n">l</span><span class="p">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">:]</span>
|
||
<span class="n">p</span> <span class="o">=</span> <span class="n">perm</span><span class="p">(</span><span class="n">l</span><span class="p">[:</span><span class="n">i</span><span class="p">]</span> <span class="o">+</span> <span class="n">l</span><span class="p">[</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">:])</span> <span class="c1"># error: unexpected indent</span>
|
||
<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">p</span><span class="p">:</span>
|
||
<span class="n">r</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">l</span><span class="p">[</span><span class="n">i</span><span class="p">:</span><span class="n">i</span><span class="o">+</span><span class="mi">1</span><span class="p">]</span> <span class="o">+</span> <span class="n">x</span><span class="p">)</span>
|
||
<span class="k">return</span> <span class="n">r</span> <span class="c1"># error: inconsistent dedent</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>（实际上，解析器可以识别前三个错误；只有最后一个错误由词法分析器识别 --- <code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">r</span></code> 的缩进无法匹配从栈里移除的缩进层级。）</p>
|
||
</section>
|
||
<section id="whitespace-between-tokens">
|
||
<span id="whitespace"></span><h3><span class="section-number">2.1.9. </span>形符间的空白字符<a class="headerlink" href="#whitespace-between-tokens" title="永久链接至标题">¶</a></h3>
|
||
<p>除非在逻辑行开头或字符串内，空格符、制表符、换页符等空白符都可以分隔形符。要把两个相连形符解读为不同形符，需要用空白符分隔（例如，ab 是一个形符，a b 则是两个形符）。</p>
|
||
</section>
|
||
</section>
|
||
<section id="other-tokens">
|
||
<span id="id7"></span><h2><span class="section-number">2.2. </span>其他形符<a class="headerlink" href="#other-tokens" title="永久链接至标题">¶</a></h2>
|
||
<p>除 NEWLINE、INDENT、DEDENT 外，还有 <em>标识符</em>、<em>关键字</em>、<em>字面值</em>、<em>运算符</em> 、<em>分隔符</em> 等形符。 空白符（前述的行终止符除外）不是形符，可用于分隔形符。存在二义性时，将从左至右，读取尽量长的字符串组成合法形符。</p>
|
||
</section>
|
||
<section id="identifiers">
|
||
<span id="identifiers-and-keywords"></span><h2><span class="section-number">2.3. </span>标识符和关键字<a class="headerlink" href="#identifiers" title="永久链接至标题">¶</a></h2>
|
||
<p id="index-10">标识符（也称为 <em>名称</em>）的词法定义说明如下。</p>
|
||
<p>Python 标识符的句法基于 Unicode 标准附件 UAX-31，并加入了下文定义的细化与修改；详见 <span class="target" id="index-38"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3131"><strong>PEP 3131</strong></a> 。</p>
|
||
<p>与 Python 2.x 一样，在 ASCII 范围内（U+0001..U+007F），有效标识符字符为： 大小写字母 <code class="docutils literal notranslate"><span class="pre">A</span></code> 至 <code class="docutils literal notranslate"><span class="pre">Z</span></code>、下划线 <code class="docutils literal notranslate"><span class="pre">_</span></code> 、数字 <code class="docutils literal notranslate"><span class="pre">0</span></code> 至 <code class="docutils literal notranslate"><span class="pre">9</span></code>，但不能以数字开头。</p>
|
||
<p>Python 3.0 引入了 ASCII 之外的更多字符（请参阅 <span class="target" id="index-39"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3131"><strong>PEP 3131</strong></a>）。这些字符的分类使用 <a class="reference internal" href="../library/unicodedata.html#module-unicodedata" title="unicodedata: Access the Unicode Database."><code class="xref py py-mod docutils literal notranslate"><span class="pre">unicodedata</span></code></a> 模块中的 Unicode 字符数据库版本。</p>
|
||
<p>标识符的长度没有限制，但区分大小写。</p>
|
||
<pre>
|
||
<strong id="grammar-token-identifier">identifier </strong> ::= <a class="reference internal" href="#grammar-token-xid-start"><code class="xref docutils literal notranslate"><span class="pre">xid_start</span></code></a> <a class="reference internal" href="#grammar-token-xid-continue"><code class="xref docutils literal notranslate"><span class="pre">xid_continue</span></code></a>*
|
||
<strong id="grammar-token-id-start">id_start </strong> ::= <all characters in general categories Lu, Ll, Lt, Lm, Lo, Nl, the underscore, and characters with the Other_ID_Start property>
|
||
<strong id="grammar-token-id-continue">id_continue </strong> ::= <all characters in <a class="reference internal" href="#grammar-token-id-start"><code class="xref docutils literal notranslate"><span class="pre">id_start</span></code></a>, plus characters in the categories Mn, Mc, Nd, Pc and others with the Other_ID_Continue property>
|
||
<strong id="grammar-token-xid-start">xid_start </strong> ::= <all characters in <a class="reference internal" href="#grammar-token-id-start"><code class="xref docutils literal notranslate"><span class="pre">id_start</span></code></a> whose NFKC normalization is in "id_start xid_continue*">
|
||
<strong id="grammar-token-xid-continue">xid_continue</strong> ::= <all characters in <a class="reference internal" href="#grammar-token-id-continue"><code class="xref docutils literal notranslate"><span class="pre">id_continue</span></code></a> whose NFKC normalization is in "id_continue*">
|
||
</pre>
|
||
<p>上述 Unicode 类别码的含义:</p>
|
||
<ul class="simple">
|
||
<li><p><em>Lu</em> - 大写字母</p></li>
|
||
<li><p><em>Ll</em> - 小写字母</p></li>
|
||
<li><p><em>Lt</em> - 词首大写字母</p></li>
|
||
<li><p><em>Lm</em> - 修饰符字母</p></li>
|
||
<li><p><em>Lo</em> - 其他字母</p></li>
|
||
<li><p><em>Nl</em> - 字母数字</p></li>
|
||
<li><p><em>Mn</em> - 非空白标识</p></li>
|
||
<li><p><em>Mc</em> - 含空白标识</p></li>
|
||
<li><p><em>Nd</em> - 十进制数字</p></li>
|
||
<li><p><em>Pc</em> - 连接标点</p></li>
|
||
<li><p><em>Other_ID_Start</em> - 由 <a class="reference external" href="http://www.unicode.org/Public/12.1.0/ucd/PropList.txt">PropList.txt</a> 定义的显式字符列表，用来支持向下兼容</p></li>
|
||
<li><p><em>Other_ID_Continue</em> - 同上</p></li>
|
||
</ul>
|
||
<p>在解析时，所有标识符都会被转换为规范形式 NFKC；标识符的比较都是基于 NFKC。</p>
|
||
<p>Unicode 4.1 中所有可用的标识符字符详见此 HTML 文件 <a class="reference external" href="https://www.unicode.org/Public/13.0.0/ucd/DerivedCoreProperties.txt">https://www.unicode.org/Public/13.0.0/ucd/DerivedCoreProperties.txt</a></p>
|
||
<section id="keywords">
|
||
<span id="id8"></span><h3><span class="section-number">2.3.1. </span>关键字<a class="headerlink" href="#keywords" title="永久链接至标题">¶</a></h3>
|
||
<p id="index-13">以下标识符为保留字，或称 <em>关键字</em>，不可用于普通标识符。关键字的拼写必须与这里列出的完全一致：</p>
|
||
<div class="highlight-text notranslate"><div class="highlight"><pre><span></span>False await else import pass
|
||
None break except in raise
|
||
True class finally is return
|
||
and continue for lambda try
|
||
as def from nonlocal while
|
||
assert del global not with
|
||
async elif if or yield
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="reserved-classes-of-identifiers">
|
||
<span id="id-classes"></span><span id="index-14"></span><h3><span class="section-number">2.3.2. </span>保留的标识符类<a class="headerlink" href="#reserved-classes-of-identifiers" title="永久链接至标题">¶</a></h3>
|
||
<p>某些标识符类（除了关键字）具有特殊含义。这些类的命名模式以下划线字符开头，并以下划线结尾：</p>
|
||
<dl>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">_*</span></code></dt><dd><p><code class="docutils literal notranslate"><span class="pre">from</span> <span class="pre">module</span> <span class="pre">import</span> <span class="pre">*</span></code> 时，不会导入。交互式解释器中，特殊标识符 <code class="docutils literal notranslate"><span class="pre">_</span></code> 用于存储最近一次求值的结果；该标识符保存在 <a class="reference internal" href="../library/builtins.html#module-builtins" title="builtins: The module that provides the built-in namespace."><code class="xref py py-mod docutils literal notranslate"><span class="pre">builtins</span></code></a> 模块里。不处于交互模式时，<code class="docutils literal notranslate"><span class="pre">_</span></code> 没有特殊含义，也没有预定义。详见 <a class="reference internal" href="simple_stmts.html#import"><span class="std std-ref">import 语句</span></a>。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">_</span></code> 常用于连接国际化文本；详见 <a class="reference internal" href="../library/gettext.html#module-gettext" title="gettext: Multilingual internationalization services."><code class="xref py py-mod docutils literal notranslate"><span class="pre">gettext</span></code></a> 模块文档。</p>
|
||
</div>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">__*__</span></code></dt><dd><p>系统定义的名称，通常简称为 "dunder" 。这些名称由解释器及其实现（包括标准库）定义。现有系统定义名称相关的论述详见 <a class="reference internal" href="datamodel.html#specialnames"><span class="std std-ref">特殊方法名称</span></a> 等章节。Python 未来版本中还将定义更多此类名称。任何情况下，<em>任何</em> 不显式遵从 <code class="docutils literal notranslate"><span class="pre">__*__</span></code> 名称的文档用法，都可能导致无警告提示的错误。</p>
|
||
</dd>
|
||
<dt><code class="docutils literal notranslate"><span class="pre">__*</span></code></dt><dd><p>类的私有名称。类定义时，此类名称以一种混合形式重写，以避免基类及派生类的 "私有" 属性之间产生名称冲突。详见 <a class="reference internal" href="expressions.html#atom-identifiers"><span class="std std-ref">标识符（名称）</span></a>。</p>
|
||
</dd>
|
||
</dl>
|
||
</section>
|
||
</section>
|
||
<section id="literals">
|
||
<span id="id9"></span><h2><span class="section-number">2.4. </span>字面值<a class="headerlink" href="#literals" title="永久链接至标题">¶</a></h2>
|
||
<p id="index-15">字面值是内置类型常量值的表示法。</p>
|
||
<section id="string-and-bytes-literals">
|
||
<span id="strings"></span><span id="index-16"></span><h3><span class="section-number">2.4.1. </span>字符串与字节串字面值<a class="headerlink" href="#string-and-bytes-literals" title="永久链接至标题">¶</a></h3>
|
||
<p>字符串字面值的词法定义如下：</p>
|
||
<pre>
|
||
<strong id="grammar-token-stringliteral">stringliteral </strong> ::= [<a class="reference internal" href="#grammar-token-stringprefix"><code class="xref docutils literal notranslate"><span class="pre">stringprefix</span></code></a>](<a class="reference internal" href="#grammar-token-shortstring"><code class="xref docutils literal notranslate"><span class="pre">shortstring</span></code></a> | <a class="reference internal" href="#grammar-token-longstring"><code class="xref docutils literal notranslate"><span class="pre">longstring</span></code></a>)
|
||
<strong id="grammar-token-stringprefix">stringprefix </strong> ::= "r" | "u" | "R" | "U" | "f" | "F"
|
||
| "fr" | "Fr" | "fR" | "FR" | "rf" | "rF" | "Rf" | "RF"
|
||
<strong id="grammar-token-shortstring">shortstring </strong> ::= "'" <a class="reference internal" href="#grammar-token-shortstringitem"><code class="xref docutils literal notranslate"><span class="pre">shortstringitem</span></code></a>* "'" | '"' <a class="reference internal" href="#grammar-token-shortstringitem"><code class="xref docutils literal notranslate"><span class="pre">shortstringitem</span></code></a>* '"'
|
||
<strong id="grammar-token-longstring">longstring </strong> ::= "'''" <a class="reference internal" href="#grammar-token-longstringitem"><code class="xref docutils literal notranslate"><span class="pre">longstringitem</span></code></a>* "'''" | '"""' <a class="reference internal" href="#grammar-token-longstringitem"><code class="xref docutils literal notranslate"><span class="pre">longstringitem</span></code></a>* '"""'
|
||
<strong id="grammar-token-shortstringitem">shortstringitem</strong> ::= <a class="reference internal" href="#grammar-token-shortstringchar"><code class="xref docutils literal notranslate"><span class="pre">shortstringchar</span></code></a> | <a class="reference internal" href="#grammar-token-stringescapeseq"><code class="xref docutils literal notranslate"><span class="pre">stringescapeseq</span></code></a>
|
||
<strong id="grammar-token-longstringitem">longstringitem </strong> ::= <a class="reference internal" href="#grammar-token-longstringchar"><code class="xref docutils literal notranslate"><span class="pre">longstringchar</span></code></a> | <a class="reference internal" href="#grammar-token-stringescapeseq"><code class="xref docutils literal notranslate"><span class="pre">stringescapeseq</span></code></a>
|
||
<strong id="grammar-token-shortstringchar">shortstringchar</strong> ::= <any source character except "\" or newline or the quote>
|
||
<strong id="grammar-token-longstringchar">longstringchar </strong> ::= <any source character except "\">
|
||
<strong id="grammar-token-stringescapeseq">stringescapeseq</strong> ::= "\" <any source character>
|
||
</pre>
|
||
<pre>
|
||
<strong id="grammar-token-bytesliteral">bytesliteral </strong> ::= <a class="reference internal" href="#grammar-token-bytesprefix"><code class="xref docutils literal notranslate"><span class="pre">bytesprefix</span></code></a>(<a class="reference internal" href="#grammar-token-shortbytes"><code class="xref docutils literal notranslate"><span class="pre">shortbytes</span></code></a> | <a class="reference internal" href="#grammar-token-longbytes"><code class="xref docutils literal notranslate"><span class="pre">longbytes</span></code></a>)
|
||
<strong id="grammar-token-bytesprefix">bytesprefix </strong> ::= "b" | "B" | "br" | "Br" | "bR" | "BR" | "rb" | "rB" | "Rb" | "RB"
|
||
<strong id="grammar-token-shortbytes">shortbytes </strong> ::= "'" <a class="reference internal" href="#grammar-token-shortbytesitem"><code class="xref docutils literal notranslate"><span class="pre">shortbytesitem</span></code></a>* "'" | '"' <a class="reference internal" href="#grammar-token-shortbytesitem"><code class="xref docutils literal notranslate"><span class="pre">shortbytesitem</span></code></a>* '"'
|
||
<strong id="grammar-token-longbytes">longbytes </strong> ::= "'''" <a class="reference internal" href="#grammar-token-longbytesitem"><code class="xref docutils literal notranslate"><span class="pre">longbytesitem</span></code></a>* "'''" | '"""' <a class="reference internal" href="#grammar-token-longbytesitem"><code class="xref docutils literal notranslate"><span class="pre">longbytesitem</span></code></a>* '"""'
|
||
<strong id="grammar-token-shortbytesitem">shortbytesitem</strong> ::= <a class="reference internal" href="#grammar-token-shortbyteschar"><code class="xref docutils literal notranslate"><span class="pre">shortbyteschar</span></code></a> | <a class="reference internal" href="#grammar-token-bytesescapeseq"><code class="xref docutils literal notranslate"><span class="pre">bytesescapeseq</span></code></a>
|
||
<strong id="grammar-token-longbytesitem">longbytesitem </strong> ::= <a class="reference internal" href="#grammar-token-longbyteschar"><code class="xref docutils literal notranslate"><span class="pre">longbyteschar</span></code></a> | <a class="reference internal" href="#grammar-token-bytesescapeseq"><code class="xref docutils literal notranslate"><span class="pre">bytesescapeseq</span></code></a>
|
||
<strong id="grammar-token-shortbyteschar">shortbyteschar</strong> ::= <any ASCII character except "\" or newline or the quote>
|
||
<strong id="grammar-token-longbyteschar">longbyteschar </strong> ::= <any ASCII character except "\">
|
||
<strong id="grammar-token-bytesescapeseq">bytesescapeseq</strong> ::= "\" <any ASCII character>
|
||
</pre>
|
||
<p>上述产生式没有说明以下句法限制，<a class="reference internal" href="#grammar-token-stringprefix"><code class="xref std std-token docutils literal notranslate"><span class="pre">stringprefix</span></code></a> 或 <a class="reference internal" href="#grammar-token-bytesprefix"><code class="xref std std-token docutils literal notranslate"><span class="pre">bytesprefix</span></code></a> 与其他字面值之间不允许有空白符。源字符集由编码声明定义；源文件没有编码声明时，默认为 UTF-8；详见 <a class="reference internal" href="#encodings"><span class="std std-ref">编码声明</span></a>。</p>
|
||
<p id="index-17">自然语言描述: 两种字面值都可以用成对单引号 (<code class="docutils literal notranslate"><span class="pre">'</span></code>) 或双引号 (<code class="docutils literal notranslate"><span class="pre">"</span></code>) 来标示首尾。它们也可以用成对的连续三个单引号或双引号来标示首尾 (这通常被称为 <em>三引号字符串</em>)。反斜杠 (<code class="docutils literal notranslate"><span class="pre">\</span></code>) 字符被用来对特殊含义的字符进行转义，例如换行，反斜杠本身或是引号等字符。</p>
|
||
<p id="index-18">字节串字面值要加前缀 <code class="docutils literal notranslate"><span class="pre">'b'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'B'</span></code>；生成的是类型 <a class="reference internal" href="../library/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a> 的实例，不是类型 <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> 的实例；字节串只能包含 ASCII 字符；字节串数值大于等于 128 时，必须用转义表示。</p>
|
||
<p id="index-19">字符串和字节串都可以加前缀 <code class="docutils literal notranslate"><span class="pre">'r'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'R'</span></code>，称为 <em class="dfn">原始字符串</em>，原始字符串把反斜杠当作原义字符，不执行转义操作。因此，原始字符串不转义 <code class="docutils literal notranslate"><span class="pre">'\U'</span></code> 和 <code class="docutils literal notranslate"><span class="pre">'\u'</span></code>。与 Python 2.x 的原始 unicode 字面值操作不同，Python 3.x 现已不支持 <code class="docutils literal notranslate"><span class="pre">'ur'</span></code> 句法。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.3 新版功能: </span>新增原始字节串 <code class="docutils literal notranslate"><span class="pre">'rb'</span></code> 前缀，是 <code class="docutils literal notranslate"><span class="pre">'br'</span></code> 的同义词。</p>
|
||
</div>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.3 新版功能: </span>支持 unicode 字面值（<code class="docutils literal notranslate"><span class="pre">u'value'</span></code>）遗留代码，简化 Python 2.x 和 3.x 并行代码库的维护工作。详见 <span class="target" id="index-40"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0414"><strong>PEP 414</strong></a>。</p>
|
||
</div>
|
||
<p id="index-21">前缀为 <code class="docutils literal notranslate"><span class="pre">'f'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'F'</span></code> 的字符串称为 <em class="dfn">格式字符串</em>；详见 <a class="reference internal" href="#f-strings"><span class="std std-ref">格式字符串字面值</span></a>。<code class="docutils literal notranslate"><span class="pre">'f'</span></code> 可与 <code class="docutils literal notranslate"><span class="pre">'r'</span></code> 连用，但不能与 <code class="docutils literal notranslate"><span class="pre">'b'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'u'</span></code> 连用，因此，可以使用原始格式字符串，但不能使用格式字节串字面值。</p>
|
||
<p>三引号字面值可以包含未转义的换行和引号（原样保留），除了连在一起的，用于终止字面值的，未经转义的三个引号。（"引号" 是启用字面值的字符，可以是 <code class="docutils literal notranslate"><span class="pre">'</span></code>，也可以是 <code class="docutils literal notranslate"><span class="pre">"</span></code>。）</p>
|
||
<p id="index-22">如未标注 <code class="docutils literal notranslate"><span class="pre">'r'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'R'</span></code> 前缀，字符串和字节串字面值中，转义序列以类似 C 标准的规则进行解释。可用的转义序列如下：</p>
|
||
<table class="docutils align-default">
|
||
<colgroup>
|
||
<col style="width: 30%" />
|
||
<col style="width: 58%" />
|
||
<col style="width: 12%" />
|
||
</colgroup>
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p>转义序列</p></th>
|
||
<th class="head"><p>含意</p></th>
|
||
<th class="head"><p>备注</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\newline</span></code></p></td>
|
||
<td><p>忽略反斜杠与换行符</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\\</span></code></p></td>
|
||
<td><p>反斜杠（<code class="docutils literal notranslate"><span class="pre">\</span></code>）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\'</span></code></p></td>
|
||
<td><p>单引号（<code class="docutils literal notranslate"><span class="pre">'</span></code>）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\"</span></code></p></td>
|
||
<td><p>双引号（<code class="docutils literal notranslate"><span class="pre">"</span></code>）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\a</span></code></p></td>
|
||
<td><p>ASCII 响铃（BEL）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\b</span></code></p></td>
|
||
<td><p>ASCII 退格符（BS）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\f</span></code></p></td>
|
||
<td><p>ASCII 换页符（FF）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\n</span></code></p></td>
|
||
<td><p>ASCII 换行符（LF）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\r</span></code></p></td>
|
||
<td><p>ASCII 回车符（CR）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\t</span></code></p></td>
|
||
<td><p>ASCII 水平制表符（TAB）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\v</span></code></p></td>
|
||
<td><p>ASCII 垂直制表符（VT）</p></td>
|
||
<td></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\ooo</span></code></p></td>
|
||
<td><p>八进制数 <em>ooo</em> 字符</p></td>
|
||
<td><p>(1,3)</p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\xhh</span></code></p></td>
|
||
<td><p>十六进制数 <em>hh</em> 字符</p></td>
|
||
<td><p>(2,3)</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p>字符串字面值专用的转义序列：</p>
|
||
<table class="docutils align-default">
|
||
<colgroup>
|
||
<col style="width: 30%" />
|
||
<col style="width: 58%" />
|
||
<col style="width: 12%" />
|
||
</colgroup>
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p>转义序列</p></th>
|
||
<th class="head"><p>含意</p></th>
|
||
<th class="head"><p>备注</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\N{name}</span></code></p></td>
|
||
<td><p>Unicode 数据库中名为 <em>name</em> 的字符</p></td>
|
||
<td><p>(4)</p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">\uxxxx</span></code></p></td>
|
||
<td><p>16 位十六进制数 <em>xxxx</em> 码位的字符</p></td>
|
||
<td><p>(5)</p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">\Uxxxxxxxx</span></code></p></td>
|
||
<td><p>32 位 16 进制数 <em>xxxxxxxx</em> 码位的字符</p></td>
|
||
<td><p>(6)</p></td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<p>注释：</p>
|
||
<ol class="arabic">
|
||
<li><p>与 C 标准一致，接受最多三个八进制数字。</p></li>
|
||
<li><p>与 C 标准不同，必须为两个十六进制数字。</p></li>
|
||
<li><p><em>字节串</em> 字面值中，十六进制数和八进制数的转义码以相应数值代表每个字节。<em>字符串</em> 字面值中，这些转义码以相应数值代表每个 Unicode 字符。</p></li>
|
||
<li><div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.3 版更改: </span>加入了对别名 <a class="footnote-reference brackets" href="#id13" id="id10">1</a> 的支持。</p>
|
||
</div>
|
||
</li>
|
||
<li><p>必须为 4 个十六进制数码。</p></li>
|
||
<li><p>表示任意 Unicode 字符。必须为 8 个十六进制数码。</p></li>
|
||
</ol>
|
||
<p id="index-23">与 C 标准不同，无法识别的转义序列在字符串里原样保留，即，<em>输出结果保留反斜杠</em>。（调试时，这种方式很有用：输错转义序列时，更容易在输出结果中识别错误。）注意，在字节串字面值内，字符串字面值专用的转义序列属于无法识别的转义序列。</p>
|
||
<blockquote>
|
||
<div><div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span>无法识别的转义序列触发 <a class="reference internal" href="../library/exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">DeprecationWarning</span></code></a>。未来的 Python 发行版将改为触发 <a class="reference internal" href="../library/exceptions.html#SyntaxWarning" title="SyntaxWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxWarning</span></code></a>，最终会改为触发 <a class="reference internal" href="../library/exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a>。</p>
|
||
</div>
|
||
</div></blockquote>
|
||
<p>即使在原始字面值中，引号也可以用反斜杠转义，但反斜杠会保留在输出结果里；例如 <code class="docutils literal notranslate"><span class="pre">r"\""</span></code> 是由两个字符组成的有效字符串字面值：反斜杠和双引号；<code class="docutils literal notranslate"><span class="pre">r"\"</span></code> 则不是有效字符串字面值（原始字符串也不能以奇数个反斜杠结尾）。尤其是，<em>原始字面值不能以单个反斜杠结尾</em> （反斜杠会转义其后的引号)。还要注意，反斜杠加换行在字面值中被解释为两个字符，而 <em>不是</em> 连续行。</p>
|
||
</section>
|
||
<section id="string-literal-concatenation">
|
||
<span id="string-concatenation"></span><h3><span class="section-number">2.4.2. </span>字符串字面值合并<a class="headerlink" href="#string-literal-concatenation" title="永久链接至标题">¶</a></h3>
|
||
<p>以空白符分隔的多个相邻字符串或字节串字面值，可用不同引号标注，等同于合并操作。因此，<code class="docutils literal notranslate"><span class="pre">"hello"</span> <span class="pre">'world'</span></code> 等价于 <code class="docutils literal notranslate"><span class="pre">"helloworld"</span></code>。此功能不需要反斜杠，即可将长字符串分为多个物理行，还可以为不同部分的字符串添加注释，例如：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">"[A-Za-z_]"</span> <span class="c1"># letter or underscore</span>
|
||
<span class="s2">"[A-Za-z0-9_]*"</span> <span class="c1"># letter, digit or underscore</span>
|
||
<span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>注意，此功能在句法层面定义，在编译时实现。在运行时，合并字符串表达式必须使用 '+' 运算符。还要注意，字面值合并可以为每个部分应用不同的引号风格（甚至混用原始字符串和三引号字符串)，格式字符串字面值也可以与纯字符串字面值合并。</p>
|
||
</section>
|
||
<section id="formatted-string-literals">
|
||
<span id="f-strings"></span><span id="index-24"></span><h3><span class="section-number">2.4.3. </span>格式字符串字面值<a class="headerlink" href="#formatted-string-literals" title="永久链接至标题">¶</a></h3>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.6 新版功能.</span></p>
|
||
</div>
|
||
<p><em class="dfn">格式字符串字面值</em> 或称 <em class="dfn">f-string</em> 是标注了 <code class="docutils literal notranslate"><span class="pre">'f'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'F'</span></code> 前缀的字符串字面值。这种字符串可包含替换字段，即以 <code class="docutils literal notranslate"><span class="pre">{}</span></code> 标注的表达式。其他字符串字面值只是常量，格式字符串字面值则是可在运行时求值的表达式。</p>
|
||
<p>除非字面值标记为原始字符串，否则，与在普通字符串字面值中一样，转义序列也会被解码。解码后，用于字符串内容的语法如下：</p>
|
||
<pre>
|
||
<strong id="grammar-token-f-string">f_string </strong> ::= (<a class="reference internal" href="#grammar-token-literal-char"><code class="xref docutils literal notranslate"><span class="pre">literal_char</span></code></a> | "{{" | "}}" | <a class="reference internal" href="#grammar-token-replacement-field"><code class="xref docutils literal notranslate"><span class="pre">replacement_field</span></code></a>)*
|
||
<strong id="grammar-token-replacement-field">replacement_field</strong> ::= "{" <a class="reference internal" href="#grammar-token-f-expression"><code class="xref docutils literal notranslate"><span class="pre">f_expression</span></code></a> ["="] ["!" <a class="reference internal" href="#grammar-token-conversion"><code class="xref docutils literal notranslate"><span class="pre">conversion</span></code></a>] [":" <a class="reference internal" href="#grammar-token-format-spec"><code class="xref docutils literal notranslate"><span class="pre">format_spec</span></code></a>] "}"
|
||
<strong id="grammar-token-f-expression">f_expression </strong> ::= (<a class="reference internal" href="expressions.html#grammar-token-conditional-expression"><code class="xref docutils literal notranslate"><span class="pre">conditional_expression</span></code></a> | "*" <a class="reference internal" href="expressions.html#grammar-token-or-expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a>)
|
||
("," <a class="reference internal" href="expressions.html#grammar-token-conditional-expression"><code class="xref docutils literal notranslate"><span class="pre">conditional_expression</span></code></a> | "," "*" <a class="reference internal" href="expressions.html#grammar-token-or-expr"><code class="xref docutils literal notranslate"><span class="pre">or_expr</span></code></a>)* [","]
|
||
| <a class="reference internal" href="expressions.html#grammar-token-yield-expression"><code class="xref docutils literal notranslate"><span class="pre">yield_expression</span></code></a>
|
||
<strong id="grammar-token-conversion">conversion </strong> ::= "s" | "r" | "a"
|
||
<strong id="grammar-token-format-spec">format_spec </strong> ::= (<a class="reference internal" href="#grammar-token-literal-char"><code class="xref docutils literal notranslate"><span class="pre">literal_char</span></code></a> | NULL | <a class="reference internal" href="#grammar-token-replacement-field"><code class="xref docutils literal notranslate"><span class="pre">replacement_field</span></code></a>)*
|
||
<strong id="grammar-token-literal-char">literal_char </strong> ::= <any code point except "{", "}" or NULL>
|
||
</pre>
|
||
<p>双花括号 <code class="docutils literal notranslate"><span class="pre">'{{'</span></code> 或 <code class="docutils literal notranslate"><span class="pre">'}}'</span></code> 被替换为单花括号，花括号外的字符串仍按字面值处理。单左花括号 <code class="docutils literal notranslate"><span class="pre">'{'</span></code> 标记以 Python 表达式开头的替换字段。在表达式后加等于号 <code class="docutils literal notranslate"><span class="pre">'='</span></code>，可在求值后，同时显示表达式文本及其结果（用于调试）。 随后是用叹号 <code class="docutils literal notranslate"><span class="pre">'!'</span></code> 标记的转换字段。还可以在冒号 <code class="docutils literal notranslate"><span class="pre">':'</span></code> 后附加格式说明符。替换字段以右花括号 <code class="docutils literal notranslate"><span class="pre">'}'</span></code> 为结尾。</p>
|
||
<p>格式字符串字面值中，表达式的处理与圆括号中的常规 Python 表达式基本一样，但也有一些不同的地方。不允许使用空表达式；<a class="reference internal" href="expressions.html#lambda"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">lambda</span></code></a> 和赋值表达式 <code class="docutils literal notranslate"><span class="pre">:=</span></code> 必须显式用圆括号标注；替换表达式可以包含换行（例如，三引号字符串中），但不能包含注释；在格式字符串字面值语境内，按从左至右的顺序，为每个表达式求值。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span>Python 3.7 以前， 因为实现的问题，不允许在格式字符串字面值表达式中使用 <a class="reference internal" href="expressions.html#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> 表达式与包含 <a class="reference internal" href="compound_stmts.html#async-for"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">for</span></code></a> 子句的推导式。</p>
|
||
</div>
|
||
<p>表达式里含等号 <code class="docutils literal notranslate"><span class="pre">'='</span></code> 时，输出内容包括表达式文本、<code class="docutils literal notranslate"><span class="pre">'='</span></code> 、求值结果。输出内容可以保留表达式中左花括号 <code class="docutils literal notranslate"><span class="pre">'{'</span></code> 后，及 <code class="docutils literal notranslate"><span class="pre">'='</span></code> 后的空格。没有指定格式时，<code class="docutils literal notranslate"><span class="pre">'='</span></code> 默认调用表达式的 <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a>。指定了格式时，默认调用表达式的 <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a>，除非声明了转换字段 <code class="docutils literal notranslate"><span class="pre">'!r'</span></code>。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.8 新版功能: </span>等号 <code class="docutils literal notranslate"><span class="pre">'='</span></code>。</p>
|
||
</div>
|
||
<p>指定了转换符时，表达式求值的结果会先转换，再格式化。转换符 <code class="docutils literal notranslate"><span class="pre">'!s'</span></code> 调用 <a class="reference internal" href="../library/stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a> 转换求值结果，<code class="docutils literal notranslate"><span class="pre">'!r'</span></code> 调用 <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a>，<code class="docutils literal notranslate"><span class="pre">'!a'</span></code> 调用 <a class="reference internal" href="../library/functions.html#ascii" title="ascii"><code class="xref py py-func docutils literal notranslate"><span class="pre">ascii()</span></code></a>。</p>
|
||
<p>输出结果的格式化使用 <a class="reference internal" href="../library/functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> 协议。格式说明符传入表达式或转换结果的 <a class="reference internal" href="datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__format__()</span></code></a> 方法。省略格式说明符，则传入空字符串。然后，格式化结果包含在整个字符串的最终值里。</p>
|
||
<p>顶层的格式说明符可以包含有嵌套的替换字段。这些嵌套字段也可以包含有自己的转换字段和 <a class="reference internal" href="../library/string.html#formatspec"><span class="std std-ref">格式说明符</span></a>，但不可再包含更深层嵌套的替换字段。这里的 <a class="reference internal" href="../library/string.html#formatspec"><span class="std std-ref">格式说明符微型语言</span></a> 与字符串 .format() 方法所使用的相同。</p>
|
||
<p>格式化字符串字面值可以拼接，但是一个替换字段不能拆分到多个字面值。</p>
|
||
<p>格式字符串字面值示例如下：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">name</span> <span class="o">=</span> <span class="s2">"Fred"</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"He said his name is </span><span class="si">{</span><span class="n">name</span><span class="si">!r}</span><span class="s2">."</span>
|
||
<span class="go">"He said his name is 'Fred'."</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"He said his name is </span><span class="si">{</span><span class="nb">repr</span><span class="p">(</span><span class="n">name</span><span class="p">)</span><span class="si">}</span><span class="s2">."</span> <span class="c1"># repr() is equivalent to !r</span>
|
||
<span class="go">"He said his name is 'Fred'."</span>
|
||
<span class="gp">>>> </span><span class="n">width</span> <span class="o">=</span> <span class="mi">10</span>
|
||
<span class="gp">>>> </span><span class="n">precision</span> <span class="o">=</span> <span class="mi">4</span>
|
||
<span class="gp">>>> </span><span class="n">value</span> <span class="o">=</span> <span class="n">decimal</span><span class="o">.</span><span class="n">Decimal</span><span class="p">(</span><span class="s2">"12.34567"</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"result: </span><span class="si">{</span><span class="n">value</span><span class="si">:{</span><span class="n">width</span><span class="si">}</span><span class="s2">.</span><span class="si">{</span><span class="n">precision</span><span class="si">}}</span><span class="s2">"</span> <span class="c1"># nested fields</span>
|
||
<span class="go">'result: 12.35'</span>
|
||
<span class="gp">>>> </span><span class="n">today</span> <span class="o">=</span> <span class="n">datetime</span><span class="p">(</span><span class="n">year</span><span class="o">=</span><span class="mi">2017</span><span class="p">,</span> <span class="n">month</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">day</span><span class="o">=</span><span class="mi">27</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">today</span><span class="si">:</span><span class="s2">%B %d, %Y</span><span class="si">}</span><span class="s2">"</span> <span class="c1"># using date format specifier</span>
|
||
<span class="go">'January 27, 2017'</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">today</span><span class="si">=:</span><span class="s2">%B %d, %Y</span><span class="si">}</span><span class="s2">"</span> <span class="c1"># using date format specifier and debugging</span>
|
||
<span class="go">'today=January 27, 2017'</span>
|
||
<span class="gp">>>> </span><span class="n">number</span> <span class="o">=</span> <span class="mi">1024</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">number</span><span class="si">:</span><span class="s2">#0x</span><span class="si">}</span><span class="s2">"</span> <span class="c1"># using integer format specifier</span>
|
||
<span class="go">'0x400'</span>
|
||
<span class="gp">>>> </span><span class="n">foo</span> <span class="o">=</span> <span class="s2">"bar"</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="w"> </span><span class="n">foo</span><span class="w"> </span><span class="si">= }</span><span class="s2">"</span> <span class="c1"># preserves whitespace</span>
|
||
<span class="go">" foo = 'bar'"</span>
|
||
<span class="gp">>>> </span><span class="n">line</span> <span class="o">=</span> <span class="s2">"The mill's closed"</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">line</span><span class="w"> </span><span class="si">= }</span><span class="s2">"</span>
|
||
<span class="go">'line = "The mill\'s closed"'</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">line</span><span class="w"> </span><span class="si">= :</span><span class="s2">20</span><span class="si">}</span><span class="s2">"</span>
|
||
<span class="go">"line = The mill's closed "</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">line</span><span class="w"> </span><span class="si">= !r:</span><span class="s2">20</span><span class="si">}</span><span class="s2">"</span>
|
||
<span class="go">'line = "The mill\'s closed" '</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>与常规字符串字面值的语法一样，替换字段中的字符不能与外层格式字符串字面值的引号冲突：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="sa">f</span><span class="s2">"abc </span><span class="si">{</span><span class="n">a</span><span class="p">[</span><span class="s2">"x"</span><span class="p">]</span><span class="si">}</span><span class="s2"> def"</span> <span class="c1"># error: outer string literal ended prematurely</span>
|
||
<span class="sa">f</span><span class="s2">"abc </span><span class="si">{</span><span class="n">a</span><span class="p">[</span><span class="s1">'x'</span><span class="p">]</span><span class="si">}</span><span class="s2"> def"</span> <span class="c1"># workaround: use different quoting</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>格式化表达式中不允许使用反斜杠，否则导致错误：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="sa">f</span><span class="s2">"newline: </span><span class="si">{</span><span class="nb">ord</span><span class="p">(</span><span class="s1">'</span><span class="se">\n</span><span class="s1">'</span><span class="p">)</span><span class="si">}</span><span class="s2">"</span> <span class="c1"># raises SyntaxError</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果要包含带反斜杠的值，请创建一个临时变量。</p>
|
||
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">newline</span> <span class="o">=</span> <span class="nb">ord</span><span class="p">(</span><span class="s1">'</span><span class="se">\n</span><span class="s1">'</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="sa">f</span><span class="s2">"newline: </span><span class="si">{</span><span class="n">newline</span><span class="si">}</span><span class="s2">"</span>
|
||
<span class="go">'newline: 10'</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>即便未包含表达式，格式字符串字面值也不能用作文档字符串。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
|
||
<span class="gp">... </span> <span class="sa">f</span><span class="s2">"Not a docstring"</span>
|
||
<span class="gp">...</span>
|
||
<span class="gp">>>> </span><span class="n">foo</span><span class="o">.</span><span class="vm">__doc__</span> <span class="ow">is</span> <span class="kc">None</span>
|
||
<span class="go">True</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>参阅 <span class="target" id="index-41"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0498"><strong>PEP 498</strong></a>，了解格式字符串字面值的提案，以及与格式字符串机制相关的 <a class="reference internal" href="../library/stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate"><span class="pre">str.format()</span></code></a>。</p>
|
||
</section>
|
||
<section id="numeric-literals">
|
||
<span id="numbers"></span><h3><span class="section-number">2.4.4. </span>数值字面值<a class="headerlink" href="#numeric-literals" title="永久链接至标题">¶</a></h3>
|
||
<p id="index-26">数值字面值有三种类型：整数、浮点数、虚数。没有复数字面值（复数由实数加虚数构成）。</p>
|
||
<p>注意，数值字面值不含正负号；实际上，<code class="docutils literal notranslate"><span class="pre">-1</span></code> 等负数是由一元运算符 '<code class="docutils literal notranslate"><span class="pre">-</span></code>' 和字面值 <code class="docutils literal notranslate"><span class="pre">1</span></code> 合成的。</p>
|
||
</section>
|
||
<section id="integer-literals">
|
||
<span id="integers"></span><span id="index-27"></span><h3><span class="section-number">2.4.5. </span>整数字面值<a class="headerlink" href="#integer-literals" title="永久链接至标题">¶</a></h3>
|
||
<p>整数字面值词法定义如下：</p>
|
||
<pre>
|
||
<strong id="grammar-token-integer">integer </strong> ::= <a class="reference internal" href="#grammar-token-decinteger"><code class="xref docutils literal notranslate"><span class="pre">decinteger</span></code></a> | <a class="reference internal" href="#grammar-token-bininteger"><code class="xref docutils literal notranslate"><span class="pre">bininteger</span></code></a> | <a class="reference internal" href="#grammar-token-octinteger"><code class="xref docutils literal notranslate"><span class="pre">octinteger</span></code></a> | <a class="reference internal" href="#grammar-token-hexinteger"><code class="xref docutils literal notranslate"><span class="pre">hexinteger</span></code></a>
|
||
<strong id="grammar-token-decinteger">decinteger </strong> ::= <a class="reference internal" href="#grammar-token-nonzerodigit"><code class="xref docutils literal notranslate"><span class="pre">nonzerodigit</span></code></a> (["_"] <a class="reference internal" href="#grammar-token-digit"><code class="xref docutils literal notranslate"><span class="pre">digit</span></code></a>)* | "0"+ (["_"] "0")*
|
||
<strong id="grammar-token-bininteger">bininteger </strong> ::= "0" ("b" | "B") (["_"] <a class="reference internal" href="#grammar-token-bindigit"><code class="xref docutils literal notranslate"><span class="pre">bindigit</span></code></a>)+
|
||
<strong id="grammar-token-octinteger">octinteger </strong> ::= "0" ("o" | "O") (["_"] <a class="reference internal" href="#grammar-token-octdigit"><code class="xref docutils literal notranslate"><span class="pre">octdigit</span></code></a>)+
|
||
<strong id="grammar-token-hexinteger">hexinteger </strong> ::= "0" ("x" | "X") (["_"] <a class="reference internal" href="#grammar-token-hexdigit"><code class="xref docutils literal notranslate"><span class="pre">hexdigit</span></code></a>)+
|
||
<strong id="grammar-token-nonzerodigit">nonzerodigit</strong> ::= "1"..."9"
|
||
<strong id="grammar-token-digit">digit </strong> ::= "0"..."9"
|
||
<strong id="grammar-token-bindigit">bindigit </strong> ::= "0" | "1"
|
||
<strong id="grammar-token-octdigit">octdigit </strong> ::= "0"..."7"
|
||
<strong id="grammar-token-hexdigit">hexdigit </strong> ::= <a class="reference internal" href="#grammar-token-digit"><code class="xref docutils literal notranslate"><span class="pre">digit</span></code></a> | "a"..."f" | "A"..."F"
|
||
</pre>
|
||
<p>整数字面值的长度没有限制，能一直大到占满可用内存。</p>
|
||
<p>确定数值时，会忽略字面值中的下划线。下划线只是为了分组数字，让数字更易读。下划线可在数字之间，也可在 <code class="docutils literal notranslate"><span class="pre">0x</span></code> 等基数说明符后。</p>
|
||
<p>注意，除了 0 以外，十进制数字的开头不允许有零。以免与 Python 3.0 版之前使用的 C 样式八进制字面值混淆。</p>
|
||
<p>整数字面值示例如下：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="mi">7</span> <span class="mi">2147483647</span> <span class="mo">0o177</span> <span class="mb">0b100110111</span>
|
||
<span class="mi">3</span> <span class="mi">79228162514264337593543950336</span> <span class="mo">0o377</span> <span class="mh">0xdeadbeef</span>
|
||
<span class="mi">100_000_000_000</span> <span class="mb">0b_1110_0101</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span>现已支持在字面值中，用下划线分组数字。</p>
|
||
</div>
|
||
</section>
|
||
<section id="floating-point-literals">
|
||
<span id="floating"></span><span id="index-28"></span><h3><span class="section-number">2.4.6. </span>浮点数字面值<a class="headerlink" href="#floating-point-literals" title="永久链接至标题">¶</a></h3>
|
||
<p>浮点数字面值词法定义如下：</p>
|
||
<pre>
|
||
<strong id="grammar-token-floatnumber">floatnumber </strong> ::= <a class="reference internal" href="#grammar-token-pointfloat"><code class="xref docutils literal notranslate"><span class="pre">pointfloat</span></code></a> | <a class="reference internal" href="#grammar-token-exponentfloat"><code class="xref docutils literal notranslate"><span class="pre">exponentfloat</span></code></a>
|
||
<strong id="grammar-token-pointfloat">pointfloat </strong> ::= [<a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a>] <a class="reference internal" href="#grammar-token-fraction"><code class="xref docutils literal notranslate"><span class="pre">fraction</span></code></a> | <a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a> "."
|
||
<strong id="grammar-token-exponentfloat">exponentfloat</strong> ::= (<a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a> | <a class="reference internal" href="#grammar-token-pointfloat"><code class="xref docutils literal notranslate"><span class="pre">pointfloat</span></code></a>) <a class="reference internal" href="#grammar-token-exponent"><code class="xref docutils literal notranslate"><span class="pre">exponent</span></code></a>
|
||
<strong id="grammar-token-digitpart">digitpart </strong> ::= <a class="reference internal" href="#grammar-token-digit"><code class="xref docutils literal notranslate"><span class="pre">digit</span></code></a> (["_"] <a class="reference internal" href="#grammar-token-digit"><code class="xref docutils literal notranslate"><span class="pre">digit</span></code></a>)*
|
||
<strong id="grammar-token-fraction">fraction </strong> ::= "." <a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a>
|
||
<strong id="grammar-token-exponent">exponent </strong> ::= ("e" | "E") ["+" | "-"] <a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a>
|
||
</pre>
|
||
<p>注意，解析时，整数和指数部分总以 10 为基数。例如，<code class="docutils literal notranslate"><span class="pre">077e010</span></code> 是合法的，表示的数值与 <code class="docutils literal notranslate"><span class="pre">77e10</span></code> 相同。浮点数字面值的支持范围取决于具体实现。整数字面值支持用下划线分组数字。</p>
|
||
<p>浮点数字面值示例如下：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="mf">3.14</span> <span class="mf">10.</span> <span class="mf">.001</span> <span class="mf">1e100</span> <span class="mf">3.14e-10</span> <span class="mf">0e0</span> <span class="mf">3.14_15_93</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.6 版更改: </span>现已支持在字面值中，用下划线分组数字。</p>
|
||
</div>
|
||
</section>
|
||
<section id="imaginary-literals">
|
||
<span id="imaginary"></span><span id="index-29"></span><h3><span class="section-number">2.4.7. </span>虚数字面值<a class="headerlink" href="#imaginary-literals" title="永久链接至标题">¶</a></h3>
|
||
<p>虚数字面值词法定义如下：</p>
|
||
<pre>
|
||
<strong id="grammar-token-imagnumber">imagnumber</strong> ::= (<a class="reference internal" href="#grammar-token-floatnumber"><code class="xref docutils literal notranslate"><span class="pre">floatnumber</span></code></a> | <a class="reference internal" href="#grammar-token-digitpart"><code class="xref docutils literal notranslate"><span class="pre">digitpart</span></code></a>) ("j" | "J")
|
||
</pre>
|
||
<p>虚数字面值生成实部为 0.0 的复数。复数由一对浮点数表示，它们的取值范围相同。创建实部不为零的复数，则需添加浮点数，例如 <code class="docutils literal notranslate"><span class="pre">(3+4j)</span></code>。虚数字面值示例如下：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="mf">3.14</span><span class="n">j</span> <span class="mf">10.</span><span class="n">j</span> <span class="mi">10</span><span class="n">j</span> <span class="mf">.001</span><span class="n">j</span> <span class="mf">1e100j</span> <span class="mf">3.14e-10</span><span class="n">j</span> <span class="mf">3.14_15_93</span><span class="n">j</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
<section id="operators">
|
||
<span id="id11"></span><h2><span class="section-number">2.5. </span>运算符<a class="headerlink" href="#operators" title="永久链接至标题">¶</a></h2>
|
||
<p id="index-30">运算符如下所示：</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>+ - * ** / // % @
|
||
<< >> & | ^ ~ :=
|
||
< > <= >= == !=
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="delimiters">
|
||
<span id="id12"></span><h2><span class="section-number">2.6. </span>分隔符<a class="headerlink" href="#delimiters" title="永久链接至标题">¶</a></h2>
|
||
<p id="index-31">以下形符在语法中为分隔符：</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>( ) [ ] { }
|
||
, : . ; @ = ->
|
||
+= -= *= /= //= %= @=
|
||
&= |= ^= >>= <<= **=
|
||
</pre></div>
|
||
</div>
|
||
<p>句点也可以用于浮点数和虚数字面值。三个连续句点表示省略符。列表后半部分是增强赋值操作符，用作词法分隔符，但也可以执行运算。</p>
|
||
<p>以下 ASCII 字符具有特殊含义，对词法分析器有重要意义：</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>' " # \
|
||
</pre></div>
|
||
</div>
|
||
<p>以下 ASCII 字符不用于 Python。在字符串字面值或注释外使用时，将直接报错：</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>$ ? `
|
||
</pre></div>
|
||
</div>
|
||
<p class="rubric">备注</p>
|
||
<dl class="footnote brackets">
|
||
<dt class="label" id="id13"><span class="brackets"><a class="fn-backref" href="#id10">1</a></span></dt>
|
||
<dd><p><a class="reference external" href="http://www.unicode.org/Public/11.0.0/ucd/NameAliases.txt">http://www.unicode.org/Public/11.0.0/ucd/NameAliases.txt</a></p>
|
||
</dd>
|
||
</dl>
|
||
</section>
|
||
</section>
|
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|
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<h3><a href="../contents.html">目录</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">2. 词法分析</a><ul>
|
||
<li><a class="reference internal" href="#line-structure">2.1. 行结构</a><ul>
|
||
<li><a class="reference internal" href="#logical-lines">2.1.1. 逻辑行</a></li>
|
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|
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|
||
<li><a class="reference internal" href="#whitespace-between-tokens">2.1.9. 形符间的空白字符</a></li>
|
||
</ul>
|
||
</li>
|
||
<li><a class="reference internal" href="#other-tokens">2.2. 其他形符</a></li>
|
||
<li><a class="reference internal" href="#identifiers">2.3. 标识符和关键字</a><ul>
|
||
<li><a class="reference internal" href="#keywords">2.3.1. 关键字</a></li>
|
||
<li><a class="reference internal" href="#reserved-classes-of-identifiers">2.3.2. 保留的标识符类</a></li>
|
||
</ul>
|
||
</li>
|
||
<li><a class="reference internal" href="#literals">2.4. 字面值</a><ul>
|
||
<li><a class="reference internal" href="#string-and-bytes-literals">2.4.1. 字符串与字节串字面值</a></li>
|
||
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|
||
<li><a class="reference internal" href="#formatted-string-literals">2.4.3. 格式字符串字面值</a></li>
|
||
<li><a class="reference internal" href="#numeric-literals">2.4.4. 数值字面值</a></li>
|
||
<li><a class="reference internal" href="#integer-literals">2.4.5. 整数字面值</a></li>
|
||
<li><a class="reference internal" href="#floating-point-literals">2.4.6. 浮点数字面值</a></li>
|
||
<li><a class="reference internal" href="#imaginary-literals">2.4.7. 虚数字面值</a></li>
|
||
</ul>
|
||
</li>
|
||
<li><a class="reference internal" href="#operators">2.5. 运算符</a></li>
|
||
<li><a class="reference internal" href="#delimiters">2.6. 分隔符</a></li>
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