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<h2 class="title"><a name="oa.alltogether"></a>11.9. 全部放在一起
</h2>
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<div></div>
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<div class="abstract">
<p>你已经看到了构造一个智能的 HTTP web 客户端的所有片断。现在让我们看看如何将它们整合到一起。</p>
</div>
<div class="example"><a name="d0e29655"></a><h3 class="title">例 11.17. <tt class="function">openanything</tt> 函数
</h3>
<p>这个函数定义在 <tt class="filename">openanything.py</tt> 中。
</p><pre class="programlisting"><span class='pykeyword'>
def</span> openAnything(source, etag=None, lastmodified=None, agent=USER_AGENT):
<span class='pycomment'># non-HTTP code omitted for brevity</span>
<span class='pykeyword'>if</span> urlparse.urlparse(source)[0] == <span class='pystring'>'http'</span>: <a name="oa.alltogether.1.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<span class='pycomment'># open URL with urllib2 </span>
request = urllib2.Request(source)
request.add_header(<span class='pystring'>'User-Agent'</span>, agent) <a name="oa.alltogether.1.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<span class='pykeyword'>if</span> etag:
request.add_header(<span class='pystring'>'If-None-Match'</span>, etag) <a name="oa.alltogether.1.3"></a><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12">
<span class='pykeyword'>if</span> lastmodified:
request.add_header(<span class='pystring'>'If-Modified-Since'</span>, lastmodified) <a name="oa.alltogether.1.4"></a><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12">
request.add_header(<span class='pystring'>'Accept-encoding'</span>, <span class='pystring'>'gzip'</span>) <a name="oa.alltogether.1.5"></a><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12">
opener = urllib2.build_opener(SmartRedirectHandler(), DefaultErrorHandler()) <a name="oa.alltogether.1.6"></a><img src="../images/callouts/6.png" alt="6" border="0" width="12" height="12">
<span class='pykeyword'>return</span> opener.open(request) <a name="oa.alltogether.1.7"></a><img src="../images/callouts/7.png" alt="7" border="0" width="12" height="12">
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left"><tt class="filename">urlparse</tt> 是一个解析 URL 的便捷的工具模块。它的主要函数也叫 <tt class="function">urlparse</tt>，接受一个 URL 并将其拆分为 tuple (scheme (协议), domain (域名), path (路径), params (参数), query string parameters (请求字符串参数), fragment identifier
(片段效验符))。当然，你唯一需要注意的就是 scheme，确认你处理的是一个 HTTP URL (<tt class="filename">urllib2</tt> 才能处理)。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">通过调用函数使用 <tt class="literal">User-Agent</tt> 向 HTTP 服务器确定你的身份。如果没有 <tt class="literal">User-Agent</tt> 被指定，你会使用一个默认的，就是定义在早期的 <tt class="filename">openanything.py</tt> 模块中的那个。你从来不会使用到默认的定义在 <tt class="filename">urllib2</tt> 中的那个。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.3"><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果给出了 <tt class="literal">ETag</tt>，要在 <tt class="literal">If-None-Match</tt> 头信息中发送它。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.4"><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果给出了最近修改日期，要在 <tt class="literal">If-Modified-Since</tt> 头信息中发送它。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.5"><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果可能要告诉服务器你要获取压缩数据。</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.6"><img src="../images/callouts/6.png" alt="6" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">使用<span class="emphasis"><em>两个</em></span> 自定义 URL 处理器创建一个 URL 开启器：<tt class="classname">SmartRedirectHandler</tt> 终于处理 <tt class="literal">301</tt> 和 <tt class="literal">302</tt> 重定向，而 <tt class="classname">DefaultErrorHandler</tt> 用于处理 <tt class="literal">304</tt>, <tt class="literal">404</tt> 以及其它的错误条件。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.1.7"><img src="../images/callouts/7.png" alt="7" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">就是这样！打开 URL 并返回一个类文件对象给调用者。</td>
</tr>
</table>
</div>
</div>
<div class="example"><a name="d0e29753"></a><h3 class="title">例 11.18. <tt class="function">fetch</tt> 函数
</h3>
<p>这个函数定义在 <tt class="filename">openanything.py</tt> 中。
</p><pre class="programlisting"><span class='pykeyword'>
def</span> fetch(source, etag=None, last_modified=None, agent=USER_AGENT):
<span class='pystring'>'''Fetch data and metadata from a URL, file, stream, or string'''</span>
result = {}
f = openAnything(source, etag, last_modified, agent) <a name="oa.alltogether.2.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
result[<span class='pystring'>'data'</span>] = f.read() <a name="oa.alltogether.2.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<span class='pykeyword'>if</span> hasattr(f, <span class='pystring'>'headers'</span>):
<span class='pycomment'># save ETag, if the server sent one </span>
result[<span class='pystring'>'etag'</span>] = f.headers.get(<span class='pystring'>'ETag'</span>) <a name="oa.alltogether.2.3"></a><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12">
<span class='pycomment'># save Last-Modified header, if the server sent one </span>
result[<span class='pystring'>'lastmodified'</span>] = f.headers.get(<span class='pystring'>'Last-Modified'</span>) <a name="oa.alltogether.2.4"></a><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12">
<span class='pykeyword'>if</span> f.headers.get(<span class='pystring'>'content-encoding'</span>, <span class='pystring'>''</span>) == <span class='pystring'>'gzip'</span>: <a name="oa.alltogether.2.5"></a><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12">
<span class='pycomment'># data came back gzip-compressed, decompress it </span>
result[<span class='pystring'>'data'</span>] = gzip.GzipFile(fileobj=StringIO(result[<span class='pystring'>'data'</span>]])).read()
<span class='pykeyword'>if</span> hasattr(f, <span class='pystring'>'url'</span>): <a name="oa.alltogether.2.6"></a><img src="../images/callouts/6.png" alt="6" border="0" width="12" height="12">
result[<span class='pystring'>'url'</span>] = f.url
result[<span class='pystring'>'status'</span>] = 200
<span class='pykeyword'>if</span> hasattr(f, <span class='pystring'>'status'</span>): <a name="oa.alltogether.2.7"></a><img src="../images/callouts/7.png" alt="7" border="0" width="12" height="12">
result[<span class='pystring'>'status'</span>] = f.status
f.close()
<span class='pykeyword'>return</span> result
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">首先，你用 URL、<tt class="literal">ETag</tt> hash、<tt class="literal">Last-Modified</tt> 日期和 <tt class="literal">User-Agent</tt> 调用 <tt class="function">openAnything</tt> 函数。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">读取从服务器返回的真实数据。这可能是被压缩的；如果是，将在后面进行解压缩。</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.3"><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">保存从服务器返回的 <tt class="literal">ETag</tt> hash，这样主调程序下一次就能把它传递给你，然后再传递给 <tt class="function">openAnything</tt>，放到 <tt class="literal">If-None-Match</tt> 头信息里发送给远程服务器。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.4"><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">也要保存 <tt class="literal">Last-Modified</tt> 数据。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.5"><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果服务器说它发送的是压缩数据，就执行解压缩。</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.6"><img src="../images/callouts/6.png" alt="6" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果你的服务器返回一个 URL 就保存它，并在查明之前假定状态代码为 <tt class="literal">200</tt>。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.2.7"><img src="../images/callouts/7.png" alt="7" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果其中一个自定义 URL 处理器捕获了一个状态代码，也要保存下来。</td>
</tr>
</table>
</div>
</div>
<div class="example"><a name="d0e29828"></a><h3 class="title">例 11.19. 使用 <tt class="filename">openanything.py</tt></h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>import</span> openanything</span>
<tt class="prompt">>>> </tt><span class="userinput">useragent = <span class='pystring'>'MyHTTPWebServicesApp/1.0'</span></span>
<tt class="prompt">>>> </tt><span class="userinput">url = <span class='pystring'>'http://diveintopython.org/redir/example301.xml'</span></span>
<tt class="prompt">>>> </tt><span class="userinput">params = openanything.fetch(url, agent=useragent)</span> <a name="oa.alltogether.3.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">params</span> <a name="oa.alltogether.3.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<span class="computeroutput">{'url': 'http://diveintomark.org/xml/atom.xml',
'lastmodified': 'Thu, 15 Apr 2004 19:45:21 GMT',
'etag': '"e842a-3e53-55d97640"',
'status': 301,
'data': '<?xml version="1.0" encoding="iso-8859-1"?>
<feed version="0.3"
<-- rest of data omitted for brevity -->'}</span>
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>if</span> params[<span class='pystring'>'status'</span>] == 301:</span> <a name="oa.alltogether.3.3"></a><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12">
<tt class="prompt">... </tt><span class="userinput">url = params[<span class='pystring'>'url'</span>]</span>
<tt class="prompt">>>> </tt><span class="userinput">newparams = openanything.fetch(</span>
<tt class="prompt">... </tt><span class="userinput">url, params[<span class='pystring'>'etag'</span>], params[<span class='pystring'>'lastmodified'</span>], useragent)</span> <a name="oa.alltogether.3.4"></a><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">newparams</span>
<span class="computeroutput">{'url': 'http://diveintomark.org/xml/atom.xml',
'lastmodified': None,
'etag': '"e842a-3e53-55d97640"',
'status': 304,
'data': ''}</span> <a name="oa.alltogether.3.5"></a><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12">
</pre><div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.3.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">第一次获取资源时，你没有 <tt class="literal">ETag</tt> hash 或 <tt class="literal">Last-Modified</tt> 日期，所以你不用使用这些参数。 (它们是<a href="../power_of_introspection/optional_arguments.html" title="4.2. 使用可选参数和命名参数">可选参数</a>。)
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.3.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">你获得了一个 dictionary，它包括几个有用的头信息、HTTP 状态代码和从服务器返回的真实数据。<tt class="filename">openanything</tt> 在内部处理 gzip 压缩；在本级别上你不必关心它。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.3.3"><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">如果你得到一个 <tt class="literal">301</tt> 状态代码，表示是个永久重定向，你需要把你的 URL 更新为新地址。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.3.4"><img src="../images/callouts/4.png" alt="4" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">第二次获取相同的资源时，你已经从以往获得了各种信息：URL (可能被更新了)、从上一次访问获得的 <tt class="literal">ETag</tt>、从上一次访问获得的 <tt class="literal">Last-Modified</tt> 日期，当然还有 <tt class="literal">User-Agent</tt>。
</td>
</tr>
<tr>
<td width="12" valign="top" align="left"><a href="#oa.alltogether.3.5"><img src="../images/callouts/5.png" alt="5" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">你重新获取了这个 dictionary，但是数据没有改变，所以你得到了一个 <tt class="literal">304</tt> 状态代码而没有数据。
</td>
</tr>
</table>
</div>
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