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<li><a class="reference internal" href="#number-1">第一种方案</a></li>
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<section id="howto-fetch-internet-resources-using-the-urllib-package">
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<span id="urllib-howto"></span><h1>如何利用 urllib 包获取网络资源<a class="headerlink" href="#howto-fetch-internet-resources-using-the-urllib-package" title="永久链接至标题">¶</a></h1>
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<dl class="field-list simple">
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<dt class="field-odd">作者</dt>
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<dd class="field-odd"><p><a class="reference external" href="http://www.voidspace.org.uk/python/index.shtml">Michael Foord</a></p>
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</dd>
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<div class="admonition note">
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<p class="admonition-title">注解</p>
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<p>这份 HOWTO 文档的早期版本有一份法语的译文，可在 <a class="reference external" href="http://www.voidspace.org.uk/python/articles/urllib2_francais.shtml">urllib2 - Le Manuel manquant</a> 处查阅。</p>
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<section id="introduction">
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<h2>概述<a class="headerlink" href="#introduction" title="永久链接至标题">¶</a></h2>
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<aside class="sidebar">
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<p class="sidebar-title">Related Articles</p>
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<p>关于如何用 Python 获取 web 资源，以下文章或许也很有用：</p>
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<ul>
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<li><p><a class="reference external" href="http://www.voidspace.org.uk/python/articles/authentication.shtml">基础的身份认证</a></p>
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<blockquote>
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<div><p><em>基本认证</em> 的教程，带有一些 Python 示例。</p>
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</div></blockquote>
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</li>
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</ul>
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</aside>
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<p><strong>urllib.request</strong> 是用于获取 URL （统一资源定位符）的 Python 模块。它以 <em>urlopen</em> 函数的形式提供了一个非常简单的接口，能用不同的协议获取 URL。同时它还为处理各种常见情形提供了一个稍微复杂一些的接口——比如：基础身份认证、cookies、代理等等。这些功能是由名为 handlers 和 opener 的对象提供的。</p>
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<p>urllib.request 支持多种 "URL 方案" （通过 URL中 <code class="docutils literal notranslate"><span class="pre">":"</span></code> 之前的字符串加以区分——如 <code class="docutils literal notranslate"><span class="pre">"ftp://python.org/"</span></code> 中的 <code class="docutils literal notranslate"><span class="pre">"ftp"</span></code>）即为采用其关联网络协议（FTP、HTTP 之类）的 URL 方案 。本教程重点关注最常用的 HTTP 场景。</p>
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<p>对于简单场景而言， <em>urlopen</em> 用起来十分容易。但只要在打开 HTTP URL 时遇到错误或非常情况，就需要对超文本传输协议有所了解才行。最全面、最权威的 HTTP 参考是 <span class="target" id="index-8"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html"><strong>RFC 2616</strong></a> 。那是一份技术文档，并没有追求可读性。本 文旨在说明 <em>urllib</em> 的用法，为了便于阅读也附带了足够详细的 HTTP 信息。本文并不是为了替代 <a class="reference internal" href="../library/urllib.request.html#module-urllib.request" title="urllib.request: Extensible library for opening URLs."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib.request</span></code></a> 文档，只是其补充说明而已。</p>
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</section>
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<section id="fetching-urls">
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<h2>获取 URL 资源<a class="headerlink" href="#fetching-urls" title="永久链接至标题">¶</a></h2>
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<p>urllib.request 最简单的使用方式如下所示：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">urllib.request</span>
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<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s1">'http://python.org/'</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
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<span class="n">html</span> <span class="o">=</span> <span class="n">response</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
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</pre></div>
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</div>
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<p>如果想通过 URL 获取资源并临时存储一下，可以采用 <a class="reference internal" href="../library/shutil.html#shutil.copyfileobj" title="shutil.copyfileobj"><code class="xref py py-func docutils literal notranslate"><span class="pre">shutil.copyfileobj()</span></code></a> 和 <a class="reference internal" href="../library/tempfile.html#tempfile.NamedTemporaryFile" title="tempfile.NamedTemporaryFile"><code class="xref py py-func docutils literal notranslate"><span class="pre">tempfile.NamedTemporaryFile()</span></code></a> 函数：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">shutil</span>
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<span class="kn">import</span> <span class="nn">tempfile</span>
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<span class="kn">import</span> <span class="nn">urllib.request</span>
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<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="s1">'http://python.org/'</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
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<span class="k">with</span> <span class="n">tempfile</span><span class="o">.</span><span class="n">NamedTemporaryFile</span><span class="p">(</span><span class="n">delete</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span> <span class="k">as</span> <span class="n">tmp_file</span><span class="p">:</span>
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<span class="n">shutil</span><span class="o">.</span><span class="n">copyfileobj</span><span class="p">(</span><span class="n">response</span><span class="p">,</span> <span class="n">tmp_file</span><span class="p">)</span>
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<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">tmp_file</span><span class="o">.</span><span class="n">name</span><span class="p">)</span> <span class="k">as</span> <span class="n">html</span><span class="p">:</span>
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<span class="k">pass</span>
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</pre></div>
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</div>
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<p>urllib 的很多用法就是这么简单（注意 URL 不仅可以 http: 开头，还可以是 ftp: 、file: 等）。不过本教程的目的是介绍更加复杂的应用场景，重点还是关注 HTTP。</p>
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<p>HTTP 以请求和响应为基础——客户端生成请求，服务器发送响应。urllib.request 用 <code class="docutils literal notranslate"><span class="pre">Request</span></code> 对象来表示要生成的 HTTP 请求。最简单的形式就是创建一个 Request 对象，指定了想要获取的 URL。用这个 Request 对象作为参数调用 <code class="docutils literal notranslate"><span class="pre">urlopen</span></code> ，将会返回该 URL 的响应对象。响应对象类似于文件对象，就是说可以对其调用 <code class="docutils literal notranslate"><span class="pre">.read()</span></code> 之类的命令：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">urllib.request</span>
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<span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="s1">'http://www.voidspace.org.uk'</span><span class="p">)</span>
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<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
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<span class="n">the_page</span> <span class="o">=</span> <span class="n">response</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
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</pre></div>
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</div>
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<p>请注意，urllib.request 用同一个 Request 接口处理所有 URL 方案。比如可生成 FTP 请求如下：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="s1">'ftp://example.com/'</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>就 HTTP 而言，Request 对象能够做两件额外的事情：首先可以把数据传给服务器。其次，可以将 <em>有关</em> 数据或请求本身的额外信息（metadata）传给服务器——这些信息将会作为 HTTP “头部”数据发送。下面依次看下。</p>
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<section id="data">
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<h3>数据<a class="headerlink" href="#data" title="永久链接至标题">¶</a></h3>
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<p>有时需要向某个 URL 发送数据，通常此 URL 会指向某个CGI（通用网关接口）脚本或其他 web 应用。对于 HTTP 而言，这通常会用所谓的 <strong>POST</strong> 请求来完成。当要把 Web 页填写的 HTML 表单提交时，浏览器通常会执行此操作。但并不是所有的 POST 都来自表单：可以用 POST 方式传输任何数据到自己的应用上。对于通常的 HTML 表单，数据需要以标准的方式编码，然后作为 <code class="docutils literal notranslate"><span class="pre">data</span></code> 参数传给 Request 对象。编码过程是用 <a class="reference internal" href="../library/urllib.parse.html#module-urllib.parse" title="urllib.parse: Parse URLs into or assemble them from components."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib.parse</span></code></a> 库的函数完成的：</p>
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||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">urllib.parse</span>
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<span class="kn">import</span> <span class="nn">urllib.request</span>
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<span class="n">url</span> <span class="o">=</span> <span class="s1">'http://www.someserver.com/cgi-bin/register.cgi'</span>
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<span class="n">values</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'name'</span> <span class="p">:</span> <span class="s1">'Michael Foord'</span><span class="p">,</span>
|
||
<span class="s1">'location'</span> <span class="p">:</span> <span class="s1">'Northampton'</span><span class="p">,</span>
|
||
<span class="s1">'language'</span> <span class="p">:</span> <span class="s1">'Python'</span> <span class="p">}</span>
|
||
|
||
<span class="n">data</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">parse</span><span class="o">.</span><span class="n">urlencode</span><span class="p">(</span><span class="n">values</span><span class="p">)</span>
|
||
<span class="n">data</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'ascii'</span><span class="p">)</span> <span class="c1"># data should be bytes</span>
|
||
<span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="n">data</span><span class="p">)</span>
|
||
<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
|
||
<span class="n">the_page</span> <span class="o">=</span> <span class="n">response</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>请注意，有时还需要采用其他编码，比如由 HTML 表单上传文件——更多细节请参见 <a class="reference external" href="https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13">HTML 规范，提交表单</a> 。</p>
|
||
<p>如果不传递 <code class="docutils literal notranslate"><span class="pre">data</span></code> 参数，urllib 将采用 <strong>GET</strong> 请求。GET 和 POST 请求有一点不同，POST 请求往往具有“副作用”，他们会以某种方式改变系统的状态。例如，从网站下一个订单，购买一大堆罐装垃圾并运送到家。 尽管 HTTP 标准明确指出 POST <em>总是</em> 要导致副作用，而 GET 请求 <em>从来不会</em> 导致副作用。但没有什么办法能阻止 GET 和 POST 请求的副作用。数据也可以在 HTTP GET 请求中传递，只要把数据编码到 URL 中即可。</p>
|
||
<p>做法如下所示：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">urllib.request</span>
|
||
<span class="gp">>>> </span><span class="kn">import</span> <span class="nn">urllib.parse</span>
|
||
<span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="p">{}</span>
|
||
<span class="gp">>>> </span><span class="n">data</span><span class="p">[</span><span class="s1">'name'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'Somebody Here'</span>
|
||
<span class="gp">>>> </span><span class="n">data</span><span class="p">[</span><span class="s1">'location'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'Northampton'</span>
|
||
<span class="gp">>>> </span><span class="n">data</span><span class="p">[</span><span class="s1">'language'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'Python'</span>
|
||
<span class="gp">>>> </span><span class="n">url_values</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">parse</span><span class="o">.</span><span class="n">urlencode</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">url_values</span><span class="p">)</span> <span class="c1"># The order may differ from below. </span>
|
||
<span class="go">name=Somebody+Here&language=Python&location=Northampton</span>
|
||
<span class="gp">>>> </span><span class="n">url</span> <span class="o">=</span> <span class="s1">'http://www.example.com/example.cgi'</span>
|
||
<span class="gp">>>> </span><span class="n">full_url</span> <span class="o">=</span> <span class="n">url</span> <span class="o">+</span> <span class="s1">'?'</span> <span class="o">+</span> <span class="n">url_values</span>
|
||
<span class="gp">>>> </span><span class="n">data</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">full_url</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>请注意，完整的 URL 是通过在其中添加 <code class="docutils literal notranslate"><span class="pre">?</span></code> 创建的，后面跟着经过编码的数据。</p>
|
||
</section>
|
||
<section id="headers">
|
||
<h3>HTTP 头部信息<a class="headerlink" href="#headers" title="永久链接至标题">¶</a></h3>
|
||
<p>下面介绍一个具体的 HTTP 头部信息，以此说明如何在 HTTP 请求加入头部信息。</p>
|
||
<p>有些网站 <a class="footnote-reference brackets" href="#id8" id="id1">1</a> 不愿被程序浏览到，或者要向不同的浏览器发送不同版本 <a class="footnote-reference brackets" href="#id9" id="id2">2</a> 的网页。默认情况下，urllib 将自身标识为“Python-urllib/xy”（其中 <code class="docutils literal notranslate"><span class="pre">x</span></code> 、 <code class="docutils literal notranslate"><span class="pre">y</span></code> 是 Python 版本的主、次版本号，例如 <code class="docutils literal notranslate"><span class="pre">Python-urllib/2.5</span></code>），这可能会让网站不知所措，或者干脆就使其无法正常工作。浏览器是通过头部信息 <code class="docutils literal notranslate"><span class="pre">User-Agent</span></code> <a class="footnote-reference brackets" href="#id10" id="id3">3</a> 来标识自己的。在创建 Request 对象时，可以传入字典形式的头部信息。以下示例将生成与之前相同的请求，只是将自身标识为某个版本的 Internet Explorer <a class="footnote-reference brackets" href="#id11" id="id4">4</a> ：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">urllib.parse</span>
|
||
<span class="kn">import</span> <span class="nn">urllib.request</span>
|
||
|
||
<span class="n">url</span> <span class="o">=</span> <span class="s1">'http://www.someserver.com/cgi-bin/register.cgi'</span>
|
||
<span class="n">user_agent</span> <span class="o">=</span> <span class="s1">'Mozilla/5.0 (Windows NT 6.1; Win64; x64)'</span>
|
||
<span class="n">values</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'name'</span><span class="p">:</span> <span class="s1">'Michael Foord'</span><span class="p">,</span>
|
||
<span class="s1">'location'</span><span class="p">:</span> <span class="s1">'Northampton'</span><span class="p">,</span>
|
||
<span class="s1">'language'</span><span class="p">:</span> <span class="s1">'Python'</span> <span class="p">}</span>
|
||
<span class="n">headers</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'User-Agent'</span><span class="p">:</span> <span class="n">user_agent</span><span class="p">}</span>
|
||
|
||
<span class="n">data</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">parse</span><span class="o">.</span><span class="n">urlencode</span><span class="p">(</span><span class="n">values</span><span class="p">)</span>
|
||
<span class="n">data</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">'ascii'</span><span class="p">)</span>
|
||
<span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="n">url</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">headers</span><span class="p">)</span>
|
||
<span class="k">with</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span> <span class="k">as</span> <span class="n">response</span><span class="p">:</span>
|
||
<span class="n">the_page</span> <span class="o">=</span> <span class="n">response</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>响应对象也有两个很有用的方法。请参阅有关 <a class="reference internal" href="#info-and-geturl">info 和 geturl</a> 部分，了解出现问题时会发生什么。</p>
|
||
</section>
|
||
</section>
|
||
<section id="handling-exceptions">
|
||
<h2>异常的处理<a class="headerlink" href="#handling-exceptions" title="永久链接至标题">¶</a></h2>
|
||
<p>如果 <em>urlopen</em> 无法处理响应信息，就会触发 <code class="xref py py-exc docutils literal notranslate"><span class="pre">URLError</span></code> 。尽管与通常的 Python API 一样，也可能触发 <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> 、 <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> 等内置异常。</p>
|
||
<p><code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 是 <code class="xref py py-exc docutils literal notranslate"><span class="pre">URLError</span></code> 的子类，当 URL 是 HTTP 的情况时将会触发。</p>
|
||
<p>上述异常类是从 <a class="reference internal" href="../library/urllib.error.html#module-urllib.error" title="urllib.error: Exception classes raised by urllib.request."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib.error</span></code></a> 模块中导出的。</p>
|
||
<section id="urlerror">
|
||
<h3>URLError<a class="headerlink" href="#urlerror" title="永久链接至标题">¶</a></h3>
|
||
<p>触发 URLError 的原因，通常是网络不通（或者没有到指定服务器的路由），或者指定的服务器不存在。这时触发的异常会带有一个 reason 属性，是一个包含错误代码和文本错误信息的元组。</p>
|
||
<p>例如：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="s1">'http://www.pretend_server.org'</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="k">try</span><span class="p">:</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span>
|
||
<span class="gp">... </span><span class="k">except</span> <span class="n">urllib</span><span class="o">.</span><span class="n">error</span><span class="o">.</span><span class="n">URLError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
|
||
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">e</span><span class="o">.</span><span class="n">reason</span><span class="p">)</span>
|
||
<span class="gp">...</span>
|
||
<span class="go">(4, 'getaddrinfo failed')</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<section id="httperror">
|
||
<h3>HTTPError<a class="headerlink" href="#httperror" title="永久链接至标题">¶</a></h3>
|
||
<p>从服务器返回的每个 HTTP 响应都包含一个数字的 “状态码”。有时该状态码表明服务器无法完成该请求。默认的处理函数将会处理这其中的一部分响应。如若响应是“redirection”，这是要求客户端从另一 URL 处获取数据，urllib 将会自行处理。对于那些无法处理的状况，urlopen 将会引发 <code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 。典型的错误包括：“404”（页面无法找到）、“403”（请求遭拒绝）和“401”（需要身份认证）。</p>
|
||
<p>全部的 HTTP 错误码请参阅 <span class="target" id="index-9"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html"><strong>RFC 2616</strong></a> 。</p>
|
||
<p><code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 实例将包含一个整数型的“code”属性，对应于服务器发来的错误。</p>
|
||
<section id="error-codes">
|
||
<h4>错误代码<a class="headerlink" href="#error-codes" title="永久链接至标题">¶</a></h4>
|
||
<p>由于默认处理函数会自行处理重定向（300 以内的错误码），而且 100--299 的状态码表示成功，因此通常只会出现 400--599 的错误码。</p>
|
||
<p><a class="reference internal" href="../library/http.server.html#http.server.BaseHTTPRequestHandler.responses" title="http.server.BaseHTTPRequestHandler.responses"><code class="xref py py-attr docutils literal notranslate"><span class="pre">http.server.BaseHTTPRequestHandler.responses</span></code></a> 是很有用的响应码字典，其中给出了 <span class="target" id="index-10"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc2616.html"><strong>RFC 2616</strong></a> 用到的所有响应代码。为方便起见，将此字典转载如下：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Table mapping response codes to messages; entries have the</span>
|
||
<span class="c1"># form {code: (shortmessage, longmessage)}.</span>
|
||
<span class="n">responses</span> <span class="o">=</span> <span class="p">{</span>
|
||
<span class="mi">100</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Continue'</span><span class="p">,</span> <span class="s1">'Request received, please continue'</span><span class="p">),</span>
|
||
<span class="mi">101</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Switching Protocols'</span><span class="p">,</span>
|
||
<span class="s1">'Switching to new protocol; obey Upgrade header'</span><span class="p">),</span>
|
||
|
||
<span class="mi">200</span><span class="p">:</span> <span class="p">(</span><span class="s1">'OK'</span><span class="p">,</span> <span class="s1">'Request fulfilled, document follows'</span><span class="p">),</span>
|
||
<span class="mi">201</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Created'</span><span class="p">,</span> <span class="s1">'Document created, URL follows'</span><span class="p">),</span>
|
||
<span class="mi">202</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Accepted'</span><span class="p">,</span>
|
||
<span class="s1">'Request accepted, processing continues off-line'</span><span class="p">),</span>
|
||
<span class="mi">203</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Non-Authoritative Information'</span><span class="p">,</span> <span class="s1">'Request fulfilled from cache'</span><span class="p">),</span>
|
||
<span class="mi">204</span><span class="p">:</span> <span class="p">(</span><span class="s1">'No Content'</span><span class="p">,</span> <span class="s1">'Request fulfilled, nothing follows'</span><span class="p">),</span>
|
||
<span class="mi">205</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Reset Content'</span><span class="p">,</span> <span class="s1">'Clear input form for further input.'</span><span class="p">),</span>
|
||
<span class="mi">206</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Partial Content'</span><span class="p">,</span> <span class="s1">'Partial content follows.'</span><span class="p">),</span>
|
||
|
||
<span class="mi">300</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Multiple Choices'</span><span class="p">,</span>
|
||
<span class="s1">'Object has several resources -- see URI list'</span><span class="p">),</span>
|
||
<span class="mi">301</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Moved Permanently'</span><span class="p">,</span> <span class="s1">'Object moved permanently -- see URI list'</span><span class="p">),</span>
|
||
<span class="mi">302</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Found'</span><span class="p">,</span> <span class="s1">'Object moved temporarily -- see URI list'</span><span class="p">),</span>
|
||
<span class="mi">303</span><span class="p">:</span> <span class="p">(</span><span class="s1">'See Other'</span><span class="p">,</span> <span class="s1">'Object moved -- see Method and URL list'</span><span class="p">),</span>
|
||
<span class="mi">304</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Not Modified'</span><span class="p">,</span>
|
||
<span class="s1">'Document has not changed since given time'</span><span class="p">),</span>
|
||
<span class="mi">305</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Use Proxy'</span><span class="p">,</span>
|
||
<span class="s1">'You must use proxy specified in Location to access this '</span>
|
||
<span class="s1">'resource.'</span><span class="p">),</span>
|
||
<span class="mi">307</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Temporary Redirect'</span><span class="p">,</span>
|
||
<span class="s1">'Object moved temporarily -- see URI list'</span><span class="p">),</span>
|
||
|
||
<span class="mi">400</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Bad Request'</span><span class="p">,</span>
|
||
<span class="s1">'Bad request syntax or unsupported method'</span><span class="p">),</span>
|
||
<span class="mi">401</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Unauthorized'</span><span class="p">,</span>
|
||
<span class="s1">'No permission -- see authorization schemes'</span><span class="p">),</span>
|
||
<span class="mi">402</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Payment Required'</span><span class="p">,</span>
|
||
<span class="s1">'No payment -- see charging schemes'</span><span class="p">),</span>
|
||
<span class="mi">403</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Forbidden'</span><span class="p">,</span>
|
||
<span class="s1">'Request forbidden -- authorization will not help'</span><span class="p">),</span>
|
||
<span class="mi">404</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Not Found'</span><span class="p">,</span> <span class="s1">'Nothing matches the given URI'</span><span class="p">),</span>
|
||
<span class="mi">405</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Method Not Allowed'</span><span class="p">,</span>
|
||
<span class="s1">'Specified method is invalid for this server.'</span><span class="p">),</span>
|
||
<span class="mi">406</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Not Acceptable'</span><span class="p">,</span> <span class="s1">'URI not available in preferred format.'</span><span class="p">),</span>
|
||
<span class="mi">407</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Proxy Authentication Required'</span><span class="p">,</span> <span class="s1">'You must authenticate with '</span>
|
||
<span class="s1">'this proxy before proceeding.'</span><span class="p">),</span>
|
||
<span class="mi">408</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Request Timeout'</span><span class="p">,</span> <span class="s1">'Request timed out; try again later.'</span><span class="p">),</span>
|
||
<span class="mi">409</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Conflict'</span><span class="p">,</span> <span class="s1">'Request conflict.'</span><span class="p">),</span>
|
||
<span class="mi">410</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Gone'</span><span class="p">,</span>
|
||
<span class="s1">'URI no longer exists and has been permanently removed.'</span><span class="p">),</span>
|
||
<span class="mi">411</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Length Required'</span><span class="p">,</span> <span class="s1">'Client must specify Content-Length.'</span><span class="p">),</span>
|
||
<span class="mi">412</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Precondition Failed'</span><span class="p">,</span> <span class="s1">'Precondition in headers is false.'</span><span class="p">),</span>
|
||
<span class="mi">413</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Request Entity Too Large'</span><span class="p">,</span> <span class="s1">'Entity is too large.'</span><span class="p">),</span>
|
||
<span class="mi">414</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Request-URI Too Long'</span><span class="p">,</span> <span class="s1">'URI is too long.'</span><span class="p">),</span>
|
||
<span class="mi">415</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Unsupported Media Type'</span><span class="p">,</span> <span class="s1">'Entity body in unsupported format.'</span><span class="p">),</span>
|
||
<span class="mi">416</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Requested Range Not Satisfiable'</span><span class="p">,</span>
|
||
<span class="s1">'Cannot satisfy request range.'</span><span class="p">),</span>
|
||
<span class="mi">417</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Expectation Failed'</span><span class="p">,</span>
|
||
<span class="s1">'Expect condition could not be satisfied.'</span><span class="p">),</span>
|
||
|
||
<span class="mi">500</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Internal Server Error'</span><span class="p">,</span> <span class="s1">'Server got itself in trouble'</span><span class="p">),</span>
|
||
<span class="mi">501</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Not Implemented'</span><span class="p">,</span>
|
||
<span class="s1">'Server does not support this operation'</span><span class="p">),</span>
|
||
<span class="mi">502</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Bad Gateway'</span><span class="p">,</span> <span class="s1">'Invalid responses from another server/proxy.'</span><span class="p">),</span>
|
||
<span class="mi">503</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Service Unavailable'</span><span class="p">,</span>
|
||
<span class="s1">'The server cannot process the request due to a high load'</span><span class="p">),</span>
|
||
<span class="mi">504</span><span class="p">:</span> <span class="p">(</span><span class="s1">'Gateway Timeout'</span><span class="p">,</span>
|
||
<span class="s1">'The gateway server did not receive a timely response'</span><span class="p">),</span>
|
||
<span class="mi">505</span><span class="p">:</span> <span class="p">(</span><span class="s1">'HTTP Version Not Supported'</span><span class="p">,</span> <span class="s1">'Cannot fulfill request.'</span><span class="p">),</span>
|
||
<span class="p">}</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>当触发错误时，服务器通过返回 HTTP 错误码 <em>和</em> 错误页面进行响应。可以将 <code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 实例用作返回页面的响应。这意味着除了 code 属性之外，错误对象还像 <code class="docutils literal notranslate"><span class="pre">urllib.response</span></code> 模块返回的那样具有 read、geturl 和 info 方法：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="s1">'http://www.python.org/fish.html'</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="k">try</span><span class="p">:</span>
|
||
<span class="gp">... </span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span>
|
||
<span class="gp">... </span><span class="k">except</span> <span class="n">urllib</span><span class="o">.</span><span class="n">error</span><span class="o">.</span><span class="n">HTTPError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
|
||
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">e</span><span class="o">.</span><span class="n">code</span><span class="p">)</span>
|
||
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">e</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
|
||
<span class="gp">...</span>
|
||
<span class="go">404</span>
|
||
<span class="go">b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"</span>
|
||
<span class="go"> "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\n\n\n<html</span>
|
||
<span class="go"> ...</span>
|
||
<span class="go"> <title>Page Not Found</title>\n</span>
|
||
<span class="go"> ...</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
<section id="wrapping-it-up">
|
||
<h3>总之<a class="headerlink" href="#wrapping-it-up" title="永久链接至标题">¶</a></h3>
|
||
<p>若要准备处理 <code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> <em>或</em> <code class="xref py py-exc docutils literal notranslate"><span class="pre">URLError</span></code> ，有两种简单的方案。推荐使用第二种方案。</p>
|
||
<section id="number-1">
|
||
<h4>第一种方案<a class="headerlink" href="#number-1" title="永久链接至标题">¶</a></h4>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">Request</span><span class="p">,</span> <span class="n">urlopen</span>
|
||
<span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">URLError</span><span class="p">,</span> <span class="n">HTTPError</span>
|
||
<span class="n">req</span> <span class="o">=</span> <span class="n">Request</span><span class="p">(</span><span class="n">someurl</span><span class="p">)</span>
|
||
<span class="k">try</span><span class="p">:</span>
|
||
<span class="n">response</span> <span class="o">=</span> <span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span>
|
||
<span class="k">except</span> <span class="n">HTTPError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'The server couldn</span><span class="se">\'</span><span class="s1">t fulfill the request.'</span><span class="p">)</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'Error code: '</span><span class="p">,</span> <span class="n">e</span><span class="o">.</span><span class="n">code</span><span class="p">)</span>
|
||
<span class="k">except</span> <span class="n">URLError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'We failed to reach a server.'</span><span class="p">)</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'Reason: '</span><span class="p">,</span> <span class="n">e</span><span class="o">.</span><span class="n">reason</span><span class="p">)</span>
|
||
<span class="k">else</span><span class="p">:</span>
|
||
<span class="c1"># everything is fine</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">except</span> <span class="pre">HTTPError</span></code> <em>必须</em> 首先处理，否则 <code class="docutils literal notranslate"><span class="pre">except</span> <span class="pre">URLError</span></code> 将会 <em>同时</em> 捕获 <code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 。</p>
|
||
</div>
|
||
</section>
|
||
<section id="number-2">
|
||
<h4>第二种方案<a class="headerlink" href="#number-2" title="永久链接至标题">¶</a></h4>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">urllib.request</span> <span class="kn">import</span> <span class="n">Request</span><span class="p">,</span> <span class="n">urlopen</span>
|
||
<span class="kn">from</span> <span class="nn">urllib.error</span> <span class="kn">import</span> <span class="n">URLError</span>
|
||
<span class="n">req</span> <span class="o">=</span> <span class="n">Request</span><span class="p">(</span><span class="n">someurl</span><span class="p">)</span>
|
||
<span class="k">try</span><span class="p">:</span>
|
||
<span class="n">response</span> <span class="o">=</span> <span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span>
|
||
<span class="k">except</span> <span class="n">URLError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
|
||
<span class="k">if</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">e</span><span class="p">,</span> <span class="s1">'reason'</span><span class="p">):</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'We failed to reach a server.'</span><span class="p">)</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'Reason: '</span><span class="p">,</span> <span class="n">e</span><span class="o">.</span><span class="n">reason</span><span class="p">)</span>
|
||
<span class="k">elif</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">e</span><span class="p">,</span> <span class="s1">'code'</span><span class="p">):</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'The server couldn</span><span class="se">\'</span><span class="s1">t fulfill the request.'</span><span class="p">)</span>
|
||
<span class="nb">print</span><span class="p">(</span><span class="s1">'Error code: '</span><span class="p">,</span> <span class="n">e</span><span class="o">.</span><span class="n">code</span><span class="p">)</span>
|
||
<span class="k">else</span><span class="p">:</span>
|
||
<span class="c1"># everything is fine</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
</section>
|
||
<section id="info-and-geturl">
|
||
<h2>info 和 geturl 方法<a class="headerlink" href="#info-and-geturl" title="永久链接至标题">¶</a></h2>
|
||
<p>由 urlopen （或者 <code class="xref py py-exc docutils literal notranslate"><span class="pre">HTTPError</span></code> 实例）所返回的响应包含两个有用的方法： <code class="xref py py-meth docutils literal notranslate"><span class="pre">info()</span></code> 和 <code class="xref py py-meth docutils literal notranslate"><span class="pre">geturl()</span></code>，该响应由模块 <a class="reference internal" href="../library/urllib.request.html#module-urllib.response" title="urllib.response: Response classes used by urllib."><code class="xref py py-mod docutils literal notranslate"><span class="pre">urllib.response</span></code></a> 定义。</p>
|
||
<p><strong>geturl</strong> ——返回所获取页面的真实 URL。该方法很有用，因为 <code class="docutils literal notranslate"><span class="pre">urlopen</span></code> （或 opener 对象）可能已经经过了一次重定向。已获取页面的 URL 未必就是所请求的 URL 。</p>
|
||
<p><strong>info</strong> - 该方法返回一个类似字典的对象，描述了所获取的页面，特别是由服务器送出的头部信息（headers） 。目前它是一个 <code class="xref py py-class docutils literal notranslate"><span class="pre">http.client.HTTPMessage</span></code> 实例。</p>
|
||
<p>典型的 HTTP 头部信息包括“Content-length”、“Content-type”等。有关 HTTP 头部信息的清单，包括含义和用途的简要说明，请参阅 <a class="reference external" href="http://jkorpela.fi/http.html">HTTP Header 快速参考</a> 。</p>
|
||
</section>
|
||
<section id="openers-and-handlers">
|
||
<h2>Opener 和 Handler<a class="headerlink" href="#openers-and-handlers" title="永久链接至标题">¶</a></h2>
|
||
<p>当获取 URL 时，会用到了一个 opener（一个类名可能经过混淆的 <a class="reference internal" href="../library/urllib.request.html#urllib.request.OpenerDirector" title="urllib.request.OpenerDirector"><code class="xref py py-class docutils literal notranslate"><span class="pre">urllib.request.OpenerDirector</span></code></a> 的实例）。通常一直会用默认的 opener ——通过 <code class="docutils literal notranslate"><span class="pre">urlopen</span></code> ——但也可以创建自定义的 opener 。opener 会用到 handler。所有的“繁重工作”都由 handler 完成。每种 handler 知道某种 URL 方案（http、ftp 等）的 URL 的打开方式，或是某方面 URL 的打开方式，例如 HTTP 重定向或 HTTP cookie。</p>
|
||
<p>若要用已安装的某个 handler 获取 URL，需要创建一个 opener 对象，例如处理 cookie 的 opener，或对重定向不做处理的 opener。</p>
|
||
<p>若要创建 opener，请实例化一个 <code class="docutils literal notranslate"><span class="pre">OpenerDirector</span></code> ，然后重复调用 <code class="docutils literal notranslate"><span class="pre">.add_handler(some_handler_instance)</span></code> 。</p>
|
||
<p>或者也可以用 <code class="docutils literal notranslate"><span class="pre">build_opener</span></code> ，这是个用单次调用创建 opener 对象的便捷函数。<code class="docutils literal notranslate"><span class="pre">build_opener</span></code> 默认会添加几个 handler，不过还提供了一种快速添加和/或覆盖默认 handler 的方法。</p>
|
||
<p>可能还需要其他类型的 handler，以便处理代理、身份认证和其他常见但稍微特殊的情况。</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">install_opener</span></code> 可用于让 <code class="docutils literal notranslate"><span class="pre">opener</span></code> 对象成为（全局）默认 opener。这意味着调用 <code class="docutils literal notranslate"><span class="pre">urlopen</span></code> 时会采用已安装的 opener。</p>
|
||
<p>opener 对象带有一个 <code class="docutils literal notranslate"><span class="pre">`open</span></code> 方法，可供直接调用以获取 url，方式与 <code class="docutils literal notranslate"><span class="pre">urlopen</span></code> 函数相同。除非是为了调用方便，否则没必要去调用 <code class="docutils literal notranslate"><span class="pre">install_opener</span></code> 。</p>
|
||
</section>
|
||
<section id="id5">
|
||
<h2>基本认证<a class="headerlink" href="#id5" title="永久链接至标题">¶</a></h2>
|
||
<p>为了说明 handler 的创建和安装过程，会用到 <code class="docutils literal notranslate"><span class="pre">HTTPBasicAuthHandler</span></code> 。有关该主题的更详细的介绍——包括基本身份认证的工作原理——请参阅 <a class="reference external" href="http://www.voidspace.org.uk/python/articles/authentication.shtml">Basic Authentication Tutorial</a> 。</p>
|
||
<p>如果需要身份认证，服务器会发送一条请求身份认证的头部信息（以及 401 错误代码）。这条信息中指明了身份认证方式和“安全区域（realm）”。格式如下所示：<code class="docutils literal notranslate"><span class="pre">WWW-Authenticate:</span> <span class="pre">SCHEME</span> <span class="pre">realm="REALM"</span></code> 。</p>
|
||
<p>例如</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>WWW-Authenticate: Basic realm="cPanel Users"
|
||
</pre></div>
|
||
</div>
|
||
<p>然后，客户端应重试发起请求，请求数据中的头部信息应包含安全区域对应的用户名和密码。这就是“基本身份认证”。为了简化此过程，可以创建 <code class="docutils literal notranslate"><span class="pre">HTTPBasicAuthHandler</span></code> 的一个实例及使用它的 opener。</p>
|
||
<p><code class="docutils literal notranslate"><span class="pre">HTTPBasicAuthHandler</span></code> 用一个名为密码管理器的对象来管理 URL、安全区域与密码、用户名之间的映射关系。如果知道确切的安全区域（来自服务器发送的身份认证头部信息），那就可以用到 <code class="docutils literal notranslate"><span class="pre">HTTPPasswordMgr</span></code> 。通常人们并不关心安全区域是什么，这时用 <code class="docutils literal notranslate"><span class="pre">HTTPPasswordMgrWithDefaultRealm</span></code> 就很方便，允许为 URL 指定默认的用户名和密码。当没有为某个安全区域提供用户名和密码时，就会用到默认值。下面用 <code class="docutils literal notranslate"><span class="pre">None</span></code> 作为 <code class="docutils literal notranslate"><span class="pre">add_password</span></code> 方法的安全区域参数，表明采用默认用户名和密码。</p>
|
||
<p>首先需要身份认证的是顶级 URL。比传给 .add_password() 的 URL 级别“更深”的 URL 也会得以匹配：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># create a password manager</span>
|
||
<span class="n">password_mgr</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">HTTPPasswordMgrWithDefaultRealm</span><span class="p">()</span>
|
||
|
||
<span class="c1"># Add the username and password.</span>
|
||
<span class="c1"># If we knew the realm, we could use it instead of None.</span>
|
||
<span class="n">top_level_url</span> <span class="o">=</span> <span class="s2">"http://example.com/foo/"</span>
|
||
<span class="n">password_mgr</span><span class="o">.</span><span class="n">add_password</span><span class="p">(</span><span class="kc">None</span><span class="p">,</span> <span class="n">top_level_url</span><span class="p">,</span> <span class="n">username</span><span class="p">,</span> <span class="n">password</span><span class="p">)</span>
|
||
|
||
<span class="n">handler</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">HTTPBasicAuthHandler</span><span class="p">(</span><span class="n">password_mgr</span><span class="p">)</span>
|
||
|
||
<span class="c1"># create "opener" (OpenerDirector instance)</span>
|
||
<span class="n">opener</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">build_opener</span><span class="p">(</span><span class="n">handler</span><span class="p">)</span>
|
||
|
||
<span class="c1"># use the opener to fetch a URL</span>
|
||
<span class="n">opener</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">a_url</span><span class="p">)</span>
|
||
|
||
<span class="c1"># Install the opener.</span>
|
||
<span class="c1"># Now all calls to urllib.request.urlopen use our opener.</span>
|
||
<span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">install_opener</span><span class="p">(</span><span class="n">opener</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>在以上例子中，只向 <code class="docutils literal notranslate"><span class="pre">build_opener</span></code> 给出了 <code class="docutils literal notranslate"><span class="pre">HTTPBasicAuthHandler</span></code> 。默认情况下，opener 会有用于处理常见状况的 handler ——<code class="docutils literal notranslate"><span class="pre">ProxyHandler</span></code> （如果设置代理的话，比如设置了环境变量 <span class="target" id="index-11"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">http_proxy</span></code> ），<code class="docutils literal notranslate"><span class="pre">UnknownHandler</span></code> 、<code class="docutils literal notranslate"><span class="pre">HTTPHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">HTTPDefaultErrorHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">HTTPRedirectHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">FTPHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">FileHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">DataHandler</span></code> 、 <code class="docutils literal notranslate"><span class="pre">HTTPErrorProcessor</span></code> 。</p>
|
||
</div>
|
||
<p><code class="docutils literal notranslate"><span class="pre">top_level_url</span></code> 其实 <em>要么</em> 是一条完整的 URL（包括 “http:” 部分和主机名及可选的端口号），比如 <code class="docutils literal notranslate"><span class="pre">"http://example.com/"</span></code> ， <em>要么</em> 是一条“访问权限”（即主机名，及可选的端口号），比如 <code class="docutils literal notranslate"><span class="pre">"example.com"</span></code> 或 <code class="docutils literal notranslate"><span class="pre">"example.com:8080"</span></code> （后一个示例包含了端口号）。访问权限 <strong>不得</strong> 包含“用户信息”部分——比如 <code class="docutils literal notranslate"><span class="pre">"joe:password@example.com"</span></code> 就不正确。</p>
|
||
</section>
|
||
<section id="proxies">
|
||
<h2>代理<a class="headerlink" href="#proxies" title="永久链接至标题">¶</a></h2>
|
||
<p><strong>urllib</strong> 将自动检测并使用代理设置。 这是通过 <code class="docutils literal notranslate"><span class="pre">ProxyHandler</span></code> 实现的，当检测到代理设置时，是正常 handler 链中的一部分。通常这是一件好事，但有时也可能会无效 <a class="footnote-reference brackets" href="#id12" id="id6">5</a>。 一种方案是配置自己的 <code class="docutils literal notranslate"><span class="pre">ProxyHandler</span></code> ，不要定义代理。 设置的步骤与 <a class="reference internal" href="#basic-authentication">Basic Authentication</a> handler 类似:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">proxy_support</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">ProxyHandler</span><span class="p">({})</span>
|
||
<span class="gp">>>> </span><span class="n">opener</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">build_opener</span><span class="p">(</span><span class="n">proxy_support</span><span class="p">)</span>
|
||
<span class="gp">>>> </span><span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">install_opener</span><span class="p">(</span><span class="n">opener</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>目前 <code class="docutils literal notranslate"><span class="pre">urllib.request</span></code> <em>尚不</em> 支持通过代理抓取 <code class="docutils literal notranslate"><span class="pre">https</span></code> 链接地址。 但此功能可以通过扩展 urllib.request 来启用，如以下例程所示 <a class="footnote-reference brackets" href="#id13" id="id7">6</a>。</p>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>如果设置了 <code class="docutils literal notranslate"><span class="pre">REQUEST_METHOD</span></code> 变量，则会忽略 <code class="docutils literal notranslate"><span class="pre">HTTP_PROXY</span></code> ；参阅 <a class="reference internal" href="../library/urllib.request.html#urllib.request.getproxies" title="urllib.request.getproxies"><code class="xref py py-func docutils literal notranslate"><span class="pre">getproxies()</span></code></a> 文档。</p>
|
||
</div>
|
||
</section>
|
||
<section id="sockets-and-layers">
|
||
<h2>套接字与分层<a class="headerlink" href="#sockets-and-layers" title="永久链接至标题">¶</a></h2>
|
||
<p>Python 获取 Web 资源的能力是分层的。urllib 用到的是 <a class="reference internal" href="../library/http.client.html#module-http.client" title="http.client: HTTP and HTTPS protocol client (requires sockets)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">http.client</span></code></a> 库，而后者又用到了套接字库。</p>
|
||
<p>从 Python 2.3 开始，可以指定套接字等待响应的超时时间。这对必须要读到网页数据的应用程序会很有用。默认情况下，套接字模块 <em>不会超时</em> 并且可以挂起。目前，套接字超时机制未暴露给 http.client 或 urllib.request 层使用。不过可以为所有套接字应用设置默认的全局超时。</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">socket</span>
|
||
<span class="kn">import</span> <span class="nn">urllib.request</span>
|
||
|
||
<span class="c1"># timeout in seconds</span>
|
||
<span class="n">timeout</span> <span class="o">=</span> <span class="mi">10</span>
|
||
<span class="n">socket</span><span class="o">.</span><span class="n">setdefaulttimeout</span><span class="p">(</span><span class="n">timeout</span><span class="p">)</span>
|
||
|
||
<span class="c1"># this call to urllib.request.urlopen now uses the default timeout</span>
|
||
<span class="c1"># we have set in the socket module</span>
|
||
<span class="n">req</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">Request</span><span class="p">(</span><span class="s1">'http://www.voidspace.org.uk'</span><span class="p">)</span>
|
||
<span class="n">response</span> <span class="o">=</span> <span class="n">urllib</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">urlopen</span><span class="p">(</span><span class="n">req</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
<hr class="docutils" />
|
||
<section id="footnotes">
|
||
<h2>备注<a class="headerlink" href="#footnotes" title="永久链接至标题">¶</a></h2>
|
||
<p>这篇文档由 John Lee 审订。</p>
|
||
<dl class="footnote brackets">
|
||
<dt class="label" id="id8"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt>
|
||
<dd><p>例如 Google。</p>
|
||
</dd>
|
||
<dt class="label" id="id9"><span class="brackets"><a class="fn-backref" href="#id2">2</a></span></dt>
|
||
<dd><p>对于网站设计而言，探测不同的浏览器是非常糟糕的做法——更为明智的做法是采用 web 标准构建网站。不幸的是，很多网站依然向不同的浏览器发送不同版本的网页。</p>
|
||
</dd>
|
||
<dt class="label" id="id10"><span class="brackets"><a class="fn-backref" href="#id3">3</a></span></dt>
|
||
<dd><p>MSIE 6 的 user-agent 信息是 <em>“Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)”</em></p>
|
||
</dd>
|
||
<dt class="label" id="id11"><span class="brackets"><a class="fn-backref" href="#id4">4</a></span></dt>
|
||
<dd><p>有关 HTTP 请求的头部信息，详情请参阅 <a class="reference internal" href="#quick-reference-to-http-headers">Quick Reference to HTTP Headers</a>。</p>
|
||
</dd>
|
||
<dt class="label" id="id12"><span class="brackets"><a class="fn-backref" href="#id6">5</a></span></dt>
|
||
<dd><p>本人必须使用代理才能在工作中访问互联网。如果尝试通过代理获取 <em>localhost</em> URL，将会遭到阻止。IE 设置为代理模式，urllib 就会获取到配置信息。为了用 localhost 服务器测试脚本，我必须阻止 urllib 使用代理。</p>
|
||
</dd>
|
||
<dt class="label" id="id13"><span class="brackets"><a class="fn-backref" href="#id7">6</a></span></dt>
|
||
<dd><p>urllib 的 SSL 代理 opener（CONNECT 方法）： <a class="reference external" href="https://code.activestate.com/recipes/456195/">ASPN Cookbook Recipe</a> 。</p>
|
||
</dd>
|
||
</dl>
|
||
</section>
|
||
</section>
|
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<div class="sphinxsidebarwrapper">
|
||
<h3><a href="../contents.html">目录</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">如何利用 urllib 包获取网络资源</a><ul>
|
||
<li><a class="reference internal" href="#introduction">概述</a></li>
|
||
<li><a class="reference internal" href="#fetching-urls">获取 URL 资源</a><ul>
|
||
<li><a class="reference internal" href="#data">数据</a></li>
|
||
<li><a class="reference internal" href="#headers">HTTP 头部信息</a></li>
|
||
</ul>
|
||
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|
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<li><a class="reference internal" href="#handling-exceptions">异常的处理</a><ul>
|
||
<li><a class="reference internal" href="#urlerror">URLError</a></li>
|
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|
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|
||
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|
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|
||
<li><a class="reference internal" href="#wrapping-it-up">总之</a><ul>
|
||
<li><a class="reference internal" href="#number-1">第一种方案</a></li>
|
||
<li><a class="reference internal" href="#number-2">第二种方案</a></li>
|
||
</ul>
|
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|
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|
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|
||
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|
||
<li><a class="reference internal" href="#openers-and-handlers">Opener 和 Handler</a></li>
|
||
<li><a class="reference internal" href="#id5">基本认证</a></li>
|
||
<li><a class="reference internal" href="#proxies">代理</a></li>
|
||
<li><a class="reference internal" href="#sockets-and-layers">套接字与分层</a></li>
|
||
<li><a class="reference internal" href="#footnotes">备注</a></li>
|
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