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clarify self.keys()

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Mark Pilgrim
2009-08-06 17:29:07 -07:00
parent 8bee9f3728
commit 2ac5acc591
1 changed files with 2 additions and 1 deletions
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special-method-names.html
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@@ -289,12 +289,13 @@ class FieldStorage:
<a> return any(item.name == key for item in self.list) <span class=u>&#x2462;</span></a>
<a> def __len__(self): <span class=u>&#x2463;</span></a>
return len(self.keys())</code></pre>
<a> return len(self.keys()) <span class=u>&#x2464;</span></a></code></pre>
<ol>
<li>Once you create an instance of the <code>cgi.FieldStorage</code> class, you can use the &#8220;<code>in</code>&#8221; operator to check whether a particular parameter was included in the query string.
<li>The <code>__contains__()</code> method is the magic that makes this work.
<li>When you say <code>if 'q' in fs</code>, Python looks for the <code>__contains__()</code> method on the <var>fs</var> object, which is defined in <code>cgi.py</code>. The value <code>'q'</code> is passed into the <code>__contains__()</code> method as the <var>key</var> argument.
<li>The same <code>FieldStorage</code> class also supports returning its length, so you can say <code>len(<var>fs</var>)</code> and it will call the <code>__len__()</code> method on the <code>FieldStorage</code> class to return the number of query parameters that it identified.
<li>The <code>self.keys()</code> method checks whether <code>self.list is None</code>, so the <code>__len__</code> method doesn&#8217;t need to duplicate this error checking.
</ol>
<h2 id=acts-like-dict>Classes That Act Like Dictionaries</h2>