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<title>11.5.2 OpenerDirector Objects </title>
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<H2><A NAME="SECTION0013520000000000000000"></A><A NAME="opener-director-objects"></A>
<BR>
11.5.2 OpenerDirector Objects
</H2>
<P>
<tt class="class">OpenerDirector</tt> instances have the following methods:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3261' xml:id='l2h-3261' class="method">add_handler</tt></b>(</nobr></td>
<td><var>handler</var>)</td></tr></table></dt>
<dd>
<var>handler</var> should be an instance of <tt class="class">BaseHandler</tt>. The
following methods are searched, and added to the possible chains (note
that HTTP errors are a special case).
<P>
<UL>
<LI><tt class="method"><var>protocol</var>_open()</tt> --
signal that the handler knows how to open <var>protocol</var> URLs.
</LI>
<LI><tt class="method">http_error_<var>type</var>()</tt> --
signal that the handler knows how to handle HTTP errors with HTTP
error code <var>type</var>.
</LI>
<LI><tt class="method"><var>protocol</var>_error()</tt> --
signal that the handler knows how to handle errors from
(non-<code>http</code>) <var>protocol</var>.
</LI>
<LI><tt class="method"><var>protocol</var>_request()</tt> --
signal that the handler knows how to pre-process <var>protocol</var>
requests.
</LI>
<LI><tt class="method"><var>protocol</var>_response()</tt> --
signal that the handler knows how to post-process <var>protocol</var>
responses.
</LI>
</UL>
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3262' xml:id='l2h-3262' class="method">open</tt></b>(</nobr></td>
<td><var>url</var><big>[</big><var>, data</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Open the given <var>url</var> (which can be a request object or a string),
optionally passing the given <var>data</var>.
Arguments, return values and exceptions raised are the same as those
of <tt class="function">urlopen()</tt> (which simply calls the <tt class="method">open()</tt> method
on the currently installed global <tt class="class">OpenerDirector</tt>).
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-3263' xml:id='l2h-3263' class="method">error</tt></b>(</nobr></td>
<td><var>proto</var><big>[</big><var>,
arg</var><big>[</big><var>, ...</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Handle an error of the given protocol. This will call the registered
error handlers for the given protocol with the given arguments (which
are protocol specific). The HTTP protocol is a special case which
uses the HTTP response code to determine the specific error handler;
refer to the <tt class="method">http_error_*()</tt> methods of the handler classes.
<P>
Return values and exceptions raised are the same as those
of <tt class="function">urlopen()</tt>.
</dl>
<P>
OpenerDirector objects open URLs in three stages:
<P>
The order in which these methods are called within each stage is
determined by sorting the handler instances.
<P>
<OL>
<LI>Every handler with a method named like
<tt class="method"><var>protocol</var>_request()</tt> has that method called to
pre-process the request.
<P>
</LI>
<LI>Handlers with a method named like
<tt class="method"><var>protocol</var>_open()</tt> are called to handle the request.
This stage ends when a handler either returns a
non-<tt class="constant">None</tt> value (ie. a response), or raises an exception
(usually URLError). Exceptions are allowed to propagate.
<P>
In fact, the above algorithm is first tried for methods named
<tt class="method">default_open</tt>. If all such methods return
<tt class="constant">None</tt>, the algorithm is repeated for methods named like
<tt class="method"><var>protocol</var>_open()</tt>. If all such methods return
<tt class="constant">None</tt>, the algorithm is repeated for methods named
<tt class="method">unknown_open()</tt>.
<P>
Note that the implementation of these methods may involve calls of
the parent <tt class="class">OpenerDirector</tt> instance's <tt class="method">.open()</tt> and
<tt class="method">.error()</tt> methods.
<P>
</LI>
<LI>Every handler with a method named like
<tt class="method"><var>protocol</var>_response()</tt> has that method called to
post-process the response.
<P>
</LI>
</OL>
<P>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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