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<title>11.5.2 OpenerDirector Objects
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<H2><A NAME=
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11.5.2 OpenerDirector Objects
<tt class=
"class">OpenerDirector
</tt> instances have the following methods:
<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>
<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).
<LI><tt class=
"method"><var>protocol
</var>_open()
</tt> --
signal that the handler knows how to open
<var>protocol
</var> URLs.
<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><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><tt class=
"method"><var>protocol
</var>_request()
</tt> --
signal that the handler knows how to pre-process
<var>protocol
</var>
<LI><tt class=
"method"><var>protocol
</var>_response()
</tt> --
signal that the handler knows how to post-process
<var>protocol
</var>
<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>
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><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>
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.
Return values and exceptions raised are the same as those
of
<tt class=
"function">urlopen()
</tt>.
OpenerDirector objects open URLs in three stages:
The order in which these methods are called within each stage is
determined by sorting the handler instances.
<LI>Every handler with a method named like
<tt class=
"method"><var>protocol
</var>_request()
</tt> has that method called to
<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.
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>.
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.
<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.
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<span class=
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2.4.2, documentation updated on
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2005.
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