18.6.2 OpenerDirector Objects
OpenerDirector instances have the following methods:
-
handler should be an instance of BaseHandler. The
following methods are searched, and added to the possible chains (note
that HTTP errors are a special case).
- protocol_open() -- signal that the handler knows how to open protocol URLs.
- http_error_type() -- signal that the handler knows how to handle HTTP errors with HTTP error code type.
- protocol_error() --
signal that the handler knows how to handle errors from
(non-
http) protocol. - protocol_request() -- signal that the handler knows how to pre-process protocol requests.
- protocol_response() -- signal that the handler knows how to post-process protocol responses.
- Open the given url (which can be a request object or a string), optionally passing the given data. Arguments, return values and exceptions raised are the same as those of urlopen() (which simply calls the open() method on the currently installed global OpenerDirector).
-
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 http_error_*() methods of the handler classes.
Return values and exceptions raised are the same as those of urlopen().
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.
- Every handler with a method named like
protocol_request() has that method called to
pre-process the request.
- Handlers with a method named like
protocol_open() are called to handle the request.
This stage ends when a handler either returns a
non-None 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 default_open. If all such methods return None, the algorithm is repeated for methods named like protocol_open(). If all such methods return None, the algorithm is repeated for methods named unknown_open().
Note that the implementation of these methods may involve calls of the parent OpenerDirector instance's .open() and .error() methods.
- Every handler with a method named like
protocol_response() has that method called to
post-process the response.
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Release 2.5, documentation updated on 19th September, 2006.