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51 | ||
52 | <H1><A NAME="SECTION004200000000000000000"></A><A NAME="dnt-type-methods"></A> | |
53 | <BR> | |
54 | 2.2 Type Methods | |
55 | ||
56 | </H1> | |
57 | ||
58 | <P> | |
59 | This section aims to give a quick fly-by on the various type methods | |
60 | you can implement and what they do. | |
61 | ||
62 | <P> | |
63 | Here is the definition of <tt class="ctype">PyTypeObject</tt>, with some fields only | |
64 | used in debug builds omitted: | |
65 | ||
66 | <P> | |
67 | <div class="verbatim"> | |
68 | <pre>typedef struct _typeobject { | |
69 | PyObject_VAR_HEAD | |
70 | char *tp_name; /* For printing, in format "<module>.<name>" */ | |
71 | int tp_basicsize, tp_itemsize; /* For allocation */ | |
72 | ||
73 | /* Methods to implement standard operations */ | |
74 | ||
75 | destructor tp_dealloc; | |
76 | printfunc tp_print; | |
77 | getattrfunc tp_getattr; | |
78 | setattrfunc tp_setattr; | |
79 | cmpfunc tp_compare; | |
80 | reprfunc tp_repr; | |
81 | ||
82 | /* Method suites for standard classes */ | |
83 | ||
84 | PyNumberMethods *tp_as_number; | |
85 | PySequenceMethods *tp_as_sequence; | |
86 | PyMappingMethods *tp_as_mapping; | |
87 | ||
88 | /* More standard operations (here for binary compatibility) */ | |
89 | ||
90 | hashfunc tp_hash; | |
91 | ternaryfunc tp_call; | |
92 | reprfunc tp_str; | |
93 | getattrofunc tp_getattro; | |
94 | setattrofunc tp_setattro; | |
95 | ||
96 | /* Functions to access object as input/output buffer */ | |
97 | PyBufferProcs *tp_as_buffer; | |
98 | ||
99 | /* Flags to define presence of optional/expanded features */ | |
100 | long tp_flags; | |
101 | ||
102 | char *tp_doc; /* Documentation string */ | |
103 | ||
104 | /* Assigned meaning in release 2.0 */ | |
105 | /* call function for all accessible objects */ | |
106 | traverseproc tp_traverse; | |
107 | ||
108 | /* delete references to contained objects */ | |
109 | inquiry tp_clear; | |
110 | ||
111 | /* Assigned meaning in release 2.1 */ | |
112 | /* rich comparisons */ | |
113 | richcmpfunc tp_richcompare; | |
114 | ||
115 | /* weak reference enabler */ | |
116 | long tp_weaklistoffset; | |
117 | ||
118 | /* Added in release 2.2 */ | |
119 | /* Iterators */ | |
120 | getiterfunc tp_iter; | |
121 | iternextfunc tp_iternext; | |
122 | ||
123 | /* Attribute descriptor and subclassing stuff */ | |
124 | struct PyMethodDef *tp_methods; | |
125 | struct PyMemberDef *tp_members; | |
126 | struct PyGetSetDef *tp_getset; | |
127 | struct _typeobject *tp_base; | |
128 | PyObject *tp_dict; | |
129 | descrgetfunc tp_descr_get; | |
130 | descrsetfunc tp_descr_set; | |
131 | long tp_dictoffset; | |
132 | initproc tp_init; | |
133 | allocfunc tp_alloc; | |
134 | newfunc tp_new; | |
135 | freefunc tp_free; /* Low-level free-memory routine */ | |
136 | inquiry tp_is_gc; /* For PyObject_IS_GC */ | |
137 | PyObject *tp_bases; | |
138 | PyObject *tp_mro; /* method resolution order */ | |
139 | PyObject *tp_cache; | |
140 | PyObject *tp_subclasses; | |
141 | PyObject *tp_weaklist; | |
142 | ||
143 | } PyTypeObject; | |
144 | </pre> | |
145 | <div class="footer"> | |
146 | <a href="typestruct.txt" type="text/plain">Download as text (original file name: <span class="file">typestruct.h</span>).</a> | |
147 | </div></div> | |
148 | ||
149 | <P> | |
150 | Now that's a <em>lot</em> of methods. Don't worry too much though - if | |
151 | you have a type you want to define, the chances are very good that you | |
152 | will only implement a handful of these. | |
153 | ||
154 | <P> | |
155 | As you probably expect by now, we're going to go over this and give | |
156 | more information about the various handlers. We won't go in the order | |
157 | they are defined in the structure, because there is a lot of | |
158 | historical baggage that impacts the ordering of the fields; be sure | |
159 | your type initialization keeps the fields in the right order! It's | |
160 | often easiest to find an example that includes all the fields you need | |
161 | (even if they're initialized to <code>0</code>) and then change the values | |
162 | to suit your new type. | |
163 | ||
164 | <P> | |
165 | <div class="verbatim"><pre> | |
166 | char *tp_name; /* For printing */ | |
167 | </pre></div> | |
168 | ||
169 | <P> | |
170 | The name of the type - as mentioned in the last section, this will | |
171 | appear in various places, almost entirely for diagnostic purposes. | |
172 | Try to choose something that will be helpful in such a situation! | |
173 | ||
174 | <P> | |
175 | <div class="verbatim"><pre> | |
176 | int tp_basicsize, tp_itemsize; /* For allocation */ | |
177 | </pre></div> | |
178 | ||
179 | <P> | |
180 | These fields tell the runtime how much memory to allocate when new | |
181 | objects of this type are created. Python has some built-in support | |
182 | for variable length structures (think: strings, lists) which is where | |
183 | the <tt class="member">tp_itemsize</tt> field comes in. This will be dealt with | |
184 | later. | |
185 | ||
186 | <P> | |
187 | <div class="verbatim"><pre> | |
188 | char *tp_doc; | |
189 | </pre></div> | |
190 | ||
191 | <P> | |
192 | Here you can put a string (or its address) that you want returned when | |
193 | the Python script references <code>obj.__doc__</code> to retrieve the | |
194 | doc string. | |
195 | ||
196 | <P> | |
197 | Now we come to the basic type methods--the ones most extension types | |
198 | will implement. | |
199 | ||
200 | <P> | |
201 | ||
202 | <p><br /></p><hr class='online-navigation' /> | |
203 | <div class='online-navigation'> | |
204 | <!--Table of Child-Links--> | |
205 | <A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a> | |
206 | ||
207 | <UL CLASS="ChildLinks"> | |
208 | <LI><A href="node26.html">2.2.1 Finalization and De-allocation</a> | |
209 | <LI><A href="node27.html">2.2.2 Object Presentation</a> | |
210 | <LI><A href="node28.html">2.2.3 Attribute Management</a> | |
211 | <UL> | |
212 | <LI><A href="node29.html">2.2.3.1 Generic Attribute Management</a> | |
213 | <LI><A href="node30.html">2.2.3.2 Type-specific Attribute Management</a> | |
214 | </ul> | |
215 | <LI><A href="node31.html">2.2.4 Object Comparison</a> | |
216 | <LI><A href="node32.html">2.2.5 Abstract Protocol Support</a> | |
217 | <LI><A href="node33.html">2.2.6 More Suggestions</a> | |
218 | </ul> | |
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255 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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