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17 | <title>11.5.2 OpenerDirector Objects </title> | |
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54 | ||
55 | <H2><A NAME="SECTION0013520000000000000000"></A><A NAME="opener-director-objects"></A> | |
56 | <BR> | |
57 | 11.5.2 OpenerDirector Objects | |
58 | </H2> | |
59 | ||
60 | <P> | |
61 | <tt class="class">OpenerDirector</tt> instances have the following methods: | |
62 | ||
63 | <P> | |
64 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
65 | <td><nobr><b><tt id='l2h-3261' xml:id='l2h-3261' class="method">add_handler</tt></b>(</nobr></td> | |
66 | <td><var>handler</var>)</td></tr></table></dt> | |
67 | <dd> | |
68 | <var>handler</var> should be an instance of <tt class="class">BaseHandler</tt>. The | |
69 | following methods are searched, and added to the possible chains (note | |
70 | that HTTP errors are a special case). | |
71 | ||
72 | <P> | |
73 | ||
74 | <UL> | |
75 | <LI><tt class="method"><var>protocol</var>_open()</tt> -- | |
76 | signal that the handler knows how to open <var>protocol</var> URLs. | |
77 | </LI> | |
78 | <LI><tt class="method">http_error_<var>type</var>()</tt> -- | |
79 | signal that the handler knows how to handle HTTP errors with HTTP | |
80 | error code <var>type</var>. | |
81 | </LI> | |
82 | <LI><tt class="method"><var>protocol</var>_error()</tt> -- | |
83 | signal that the handler knows how to handle errors from | |
84 | (non-<code>http</code>) <var>protocol</var>. | |
85 | </LI> | |
86 | <LI><tt class="method"><var>protocol</var>_request()</tt> -- | |
87 | signal that the handler knows how to pre-process <var>protocol</var> | |
88 | requests. | |
89 | </LI> | |
90 | <LI><tt class="method"><var>protocol</var>_response()</tt> -- | |
91 | signal that the handler knows how to post-process <var>protocol</var> | |
92 | responses. | |
93 | </LI> | |
94 | </UL> | |
95 | </dl> | |
96 | ||
97 | <P> | |
98 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
99 | <td><nobr><b><tt id='l2h-3262' xml:id='l2h-3262' class="method">open</tt></b>(</nobr></td> | |
100 | <td><var>url</var><big>[</big><var>, data</var><big>]</big><var></var>)</td></tr></table></dt> | |
101 | <dd> | |
102 | Open the given <var>url</var> (which can be a request object or a string), | |
103 | optionally passing the given <var>data</var>. | |
104 | Arguments, return values and exceptions raised are the same as those | |
105 | of <tt class="function">urlopen()</tt> (which simply calls the <tt class="method">open()</tt> method | |
106 | on the currently installed global <tt class="class">OpenerDirector</tt>). | |
107 | </dl> | |
108 | ||
109 | <P> | |
110 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
111 | <td><nobr><b><tt id='l2h-3263' xml:id='l2h-3263' class="method">error</tt></b>(</nobr></td> | |
112 | <td><var>proto</var><big>[</big><var>, | |
113 | arg</var><big>[</big><var>, ...</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
114 | <dd> | |
115 | Handle an error of the given protocol. This will call the registered | |
116 | error handlers for the given protocol with the given arguments (which | |
117 | are protocol specific). The HTTP protocol is a special case which | |
118 | uses the HTTP response code to determine the specific error handler; | |
119 | refer to the <tt class="method">http_error_*()</tt> methods of the handler classes. | |
120 | ||
121 | <P> | |
122 | Return values and exceptions raised are the same as those | |
123 | of <tt class="function">urlopen()</tt>. | |
124 | </dl> | |
125 | ||
126 | <P> | |
127 | OpenerDirector objects open URLs in three stages: | |
128 | ||
129 | <P> | |
130 | The order in which these methods are called within each stage is | |
131 | determined by sorting the handler instances. | |
132 | ||
133 | <P> | |
134 | ||
135 | <OL> | |
136 | <LI>Every handler with a method named like | |
137 | <tt class="method"><var>protocol</var>_request()</tt> has that method called to | |
138 | pre-process the request. | |
139 | ||
140 | <P> | |
141 | </LI> | |
142 | <LI>Handlers with a method named like | |
143 | <tt class="method"><var>protocol</var>_open()</tt> are called to handle the request. | |
144 | This stage ends when a handler either returns a | |
145 | non-<tt class="constant">None</tt> value (ie. a response), or raises an exception | |
146 | (usually URLError). Exceptions are allowed to propagate. | |
147 | ||
148 | <P> | |
149 | In fact, the above algorithm is first tried for methods named | |
150 | <tt class="method">default_open</tt>. If all such methods return | |
151 | <tt class="constant">None</tt>, the algorithm is repeated for methods named like | |
152 | <tt class="method"><var>protocol</var>_open()</tt>. If all such methods return | |
153 | <tt class="constant">None</tt>, the algorithm is repeated for methods named | |
154 | <tt class="method">unknown_open()</tt>. | |
155 | ||
156 | <P> | |
157 | Note that the implementation of these methods may involve calls of | |
158 | the parent <tt class="class">OpenerDirector</tt> instance's <tt class="method">.open()</tt> and | |
159 | <tt class="method">.error()</tt> methods. | |
160 | ||
161 | <P> | |
162 | </LI> | |
163 | <LI>Every handler with a method named like | |
164 | <tt class="method"><var>protocol</var>_response()</tt> has that method called to | |
165 | post-process the response. | |
166 | ||
167 | <P> | |
168 | </LI> | |
169 | </OL> | |
170 | ||
171 | <P> | |
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207 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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