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55 | <H1><A NAME="SECTION0012300000000000000000"></A><A NAME="type-structs"></A> | |
56 | <BR> | |
57 | 10.3 Type Objects | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | Perhaps one of the most important structures of the Python object | |
62 | system is the structure that defines a new type: the | |
63 | <tt class="ctype">PyTypeObject</tt> structure. Type objects can be handled using any | |
64 | of the <tt class="cfunction">PyObject_*()</tt> or <tt class="cfunction">PyType_*()</tt> functions, | |
65 | but do not offer much that's interesting to most Python applications. | |
66 | These objects are fundamental to how objects behave, so they are very | |
67 | important to the interpreter itself and to any extension module that | |
68 | implements new types. | |
69 | ||
70 | <P> | |
71 | Type objects are fairly large compared to most of the standard types. | |
72 | The reason for the size is that each type object stores a large number | |
73 | of values, mostly C function pointers, each of which implements a | |
74 | small part of the type's functionality. The fields of the type object | |
75 | are examined in detail in this section. The fields will be described | |
76 | in the order in which they occur in the structure. | |
77 | ||
78 | <P> | |
79 | Typedefs: | |
80 | unaryfunc, binaryfunc, ternaryfunc, inquiry, coercion, intargfunc, | |
81 | intintargfunc, intobjargproc, intintobjargproc, objobjargproc, | |
82 | destructor, freefunc, printfunc, getattrfunc, getattrofunc, setattrfunc, | |
83 | setattrofunc, cmpfunc, reprfunc, hashfunc | |
84 | ||
85 | <P> | |
86 | The structure definition for <tt class="ctype">PyTypeObject</tt> can be found in | |
87 | <span class="file">Include/object.h</span>. For convenience of reference, this repeats | |
88 | the definition found there: | |
89 | ||
90 | <P> | |
91 | <div class="verbatim"> | |
92 | <pre>typedef struct _typeobject { | |
93 | PyObject_VAR_HEAD | |
94 | char *tp_name; /* For printing, in format "<module>.<name>" */ | |
95 | int tp_basicsize, tp_itemsize; /* For allocation */ | |
96 | ||
97 | /* Methods to implement standard operations */ | |
98 | ||
99 | destructor tp_dealloc; | |
100 | printfunc tp_print; | |
101 | getattrfunc tp_getattr; | |
102 | setattrfunc tp_setattr; | |
103 | cmpfunc tp_compare; | |
104 | reprfunc tp_repr; | |
105 | ||
106 | /* Method suites for standard classes */ | |
107 | ||
108 | PyNumberMethods *tp_as_number; | |
109 | PySequenceMethods *tp_as_sequence; | |
110 | PyMappingMethods *tp_as_mapping; | |
111 | ||
112 | /* More standard operations (here for binary compatibility) */ | |
113 | ||
114 | hashfunc tp_hash; | |
115 | ternaryfunc tp_call; | |
116 | reprfunc tp_str; | |
117 | getattrofunc tp_getattro; | |
118 | setattrofunc tp_setattro; | |
119 | ||
120 | /* Functions to access object as input/output buffer */ | |
121 | PyBufferProcs *tp_as_buffer; | |
122 | ||
123 | /* Flags to define presence of optional/expanded features */ | |
124 | long tp_flags; | |
125 | ||
126 | char *tp_doc; /* Documentation string */ | |
127 | ||
128 | /* Assigned meaning in release 2.0 */ | |
129 | /* call function for all accessible objects */ | |
130 | traverseproc tp_traverse; | |
131 | ||
132 | /* delete references to contained objects */ | |
133 | inquiry tp_clear; | |
134 | ||
135 | /* Assigned meaning in release 2.1 */ | |
136 | /* rich comparisons */ | |
137 | richcmpfunc tp_richcompare; | |
138 | ||
139 | /* weak reference enabler */ | |
140 | long tp_weaklistoffset; | |
141 | ||
142 | /* Added in release 2.2 */ | |
143 | /* Iterators */ | |
144 | getiterfunc tp_iter; | |
145 | iternextfunc tp_iternext; | |
146 | ||
147 | /* Attribute descriptor and subclassing stuff */ | |
148 | struct PyMethodDef *tp_methods; | |
149 | struct PyMemberDef *tp_members; | |
150 | struct PyGetSetDef *tp_getset; | |
151 | struct _typeobject *tp_base; | |
152 | PyObject *tp_dict; | |
153 | descrgetfunc tp_descr_get; | |
154 | descrsetfunc tp_descr_set; | |
155 | long tp_dictoffset; | |
156 | initproc tp_init; | |
157 | allocfunc tp_alloc; | |
158 | newfunc tp_new; | |
159 | freefunc tp_free; /* Low-level free-memory routine */ | |
160 | inquiry tp_is_gc; /* For PyObject_IS_GC */ | |
161 | PyObject *tp_bases; | |
162 | PyObject *tp_mro; /* method resolution order */ | |
163 | PyObject *tp_cache; | |
164 | PyObject *tp_subclasses; | |
165 | PyObject *tp_weaklist; | |
166 | ||
167 | } PyTypeObject; | |
168 | </pre> | |
169 | <div class="footer"> | |
170 | <a href="typestruct.txt" type="text/plain">Download as text (original file name: <span class="file">typestruct.h</span>).</a> | |
171 | </div></div> | |
172 | ||
173 | <P> | |
174 | The type object structure extends the <tt class="ctype">PyVarObject</tt> structure. | |
175 | The <tt class="member">ob_size</tt> field is used for dynamic types (created | |
176 | by <tt class="function">type_new()</tt>, usually called from a class statement). | |
177 | Note that <tt class="cdata">PyType_Type</tt> (the metatype) initializes | |
178 | <tt class="member">tp_itemsize</tt>, which means that its instances (i.e. type | |
179 | objects) <em>must</em> have the <tt class="member">ob_size</tt> field. | |
180 | ||
181 | <P> | |
182 | <dl><dt>PyObject* <b><tt id='l2h-937' xml:id='l2h-937' class="cmember">_ob_next</tt></b></dt> | |
183 | <dd> | |
184 | <dt>PyObject* <b><tt id='l2h-1002' xml:id='l2h-1002' class="cmember">_ob_prev</tt></b></dt> | |
185 | <dd> | |
186 | These fields are only present when the macro <code>Py_TRACE_REFS</code> is | |
187 | defined. Their initialization to <tt class="constant">NULL</tt> is taken care of by the | |
188 | <code>PyObject_HEAD_INIT</code> macro. For statically allocated objects, | |
189 | these fields always remain <tt class="constant">NULL</tt>. For dynamically allocated | |
190 | objects, these two fields are used to link the object into a | |
191 | doubly-linked list of <em>all</em> live objects on the heap. This | |
192 | could be used for various debugging purposes; currently the only use | |
193 | is to print the objects that are still alive at the end of a run | |
194 | when the environment variable <a class="envvar" id='l2h-1003' xml:id='l2h-1003'>PYTHONDUMPREFS</a> is set. | |
195 | ||
196 | <P> | |
197 | These fields are not inherited by subtypes. | |
198 | </dl> | |
199 | ||
200 | <P> | |
201 | <dl><dt>int <b><tt id='l2h-938' xml:id='l2h-938' class="cmember">ob_refcnt</tt></b></dt> | |
202 | <dd> | |
203 | This is the type object's reference count, initialized to <code>1</code> | |
204 | by the <code>PyObject_HEAD_INIT</code> macro. Note that for statically | |
205 | allocated type objects, the type's instances (objects whose | |
206 | <tt class="member">ob_type</tt> points back to the type) do <em>not</em> count as | |
207 | references. But for dynamically allocated type objects, the | |
208 | instances <em>do</em> count as references. | |
209 | ||
210 | <P> | |
211 | This field is not inherited by subtypes. | |
212 | </dl> | |
213 | ||
214 | <P> | |
215 | <dl><dt>PyTypeObject* <b><tt id='l2h-939' xml:id='l2h-939' class="cmember">ob_type</tt></b></dt> | |
216 | <dd> | |
217 | This is the type's type, in other words its metatype. It is | |
218 | initialized by the argument to the <code>PyObject_HEAD_INIT</code> macro, | |
219 | and its value should normally be <code>&PyType_Type</code>. However, for | |
220 | dynamically loadable extension modules that must be usable on | |
221 | Windows (at least), the compiler complains that this is not a valid | |
222 | initializer. Therefore, the convention is to pass <tt class="constant">NULL</tt> to the | |
223 | <code>PyObject_HEAD_INIT</code> macro and to initialize this field | |
224 | explicitly at the start of the module's initialization function, | |
225 | before doing anything else. This is typically done like this: | |
226 | ||
227 | <P> | |
228 | <div class="verbatim"><pre> | |
229 | Foo_Type.ob_type = &PyType_Type; | |
230 | </pre></div> | |
231 | ||
232 | <P> | |
233 | This should be done before any instances of the type are created. | |
234 | <tt class="cfunction">PyType_Ready()</tt> checks if <tt class="member">ob_type</tt> is <tt class="constant">NULL</tt>, and | |
235 | if so, initializes it: in Python 2.2, it is set to | |
236 | <code>&PyType_Type</code>; in Python 2.2.1 and later it is | |
237 | initialized to the <tt class="member">ob_type</tt> field of the base class. | |
238 | <tt class="cfunction">PyType_Ready()</tt> will not change this field if it is | |
239 | non-zero. | |
240 | ||
241 | <P> | |
242 | In Python 2.2, this field is not inherited by subtypes. In 2.2.1, | |
243 | and in 2.3 and beyond, it is inherited by subtypes. | |
244 | </dl> | |
245 | ||
246 | <P> | |
247 | <dl><dt>int <b><tt id='l2h-940' xml:id='l2h-940' class="cmember">ob_size</tt></b></dt> | |
248 | <dd> | |
249 | For statically allocated type objects, this should be initialized | |
250 | to zero. For dynamically allocated type objects, this field has a | |
251 | special internal meaning. | |
252 | ||
253 | <P> | |
254 | This field is not inherited by subtypes. | |
255 | </dl> | |
256 | ||
257 | <P> | |
258 | <dl><dt>char* <b><tt id='l2h-941' xml:id='l2h-941' class="cmember">tp_name</tt></b></dt> | |
259 | <dd> | |
260 | Pointer to a NUL-terminated string containing the name of the type. | |
261 | For types that are accessible as module globals, the string should | |
262 | be the full module name, followed by a dot, followed by the type | |
263 | name; for built-in types, it should be just the type name. If the | |
264 | module is a submodule of a package, the full package name is part of | |
265 | the full module name. For example, a type named <tt class="class">T</tt> defined | |
266 | in module <tt class="module">M</tt> in subpackage <tt class="module">Q</tt> in package <tt class="module">P</tt> | |
267 | should have the <tt class="member">tp_name</tt> initializer <code>"P.Q.M.T"</code>. | |
268 | ||
269 | <P> | |
270 | For dynamically allocated type objects, this should just be the type | |
271 | name, and the module name explicitly stored in the type dict as the | |
272 | value for key <code>'__module__'</code>. | |
273 | ||
274 | <P> | |
275 | For statically allocated type objects, the tp_name field should | |
276 | contain a dot. Everything before the last dot is made accessible as | |
277 | the <tt class="member">__module__</tt> attribute, and everything after the last dot | |
278 | is made accessible as the <tt class="member">__name__</tt> attribute. | |
279 | ||
280 | <P> | |
281 | If no dot is present, the entire <tt class="member">tp_name</tt> field is made | |
282 | accessible as the <tt class="member">__name__</tt> attribute, and the | |
283 | <tt class="member">__module__</tt> attribute is undefined (unless explicitly set in | |
284 | the dictionary, as explained above). This means your type will be | |
285 | impossible to pickle. | |
286 | ||
287 | <P> | |
288 | This field is not inherited by subtypes. | |
289 | </dl> | |
290 | ||
291 | <P> | |
292 | <dl><dt>int <b><tt id='l2h-942' xml:id='l2h-942' class="cmember">tp_basicsize</tt></b></dt> | |
293 | <dd> | |
294 | <dt>int <b><tt id='l2h-1004' xml:id='l2h-1004' class="cmember">tp_itemsize</tt></b></dt> | |
295 | <dd> | |
296 | These fields allow calculating the size in bytes of instances of | |
297 | the type. | |
298 | ||
299 | <P> | |
300 | There are two kinds of types: types with fixed-length instances have | |
301 | a zero <tt class="member">tp_itemsize</tt> field, types with variable-length | |
302 | instances have a non-zero <tt class="member">tp_itemsize</tt> field. For a type | |
303 | with fixed-length instances, all instances have the same size, | |
304 | given in <tt class="member">tp_basicsize</tt>. | |
305 | ||
306 | <P> | |
307 | For a type with variable-length instances, the instances must have | |
308 | an <tt class="member">ob_size</tt> field, and the instance size is | |
309 | <tt class="member">tp_basicsize</tt> plus N times <tt class="member">tp_itemsize</tt>, where N is | |
310 | the ``length'' of the object. The value of N is typically stored in | |
311 | the instance's <tt class="member">ob_size</tt> field. There are exceptions: for | |
312 | example, long ints use a negative <tt class="member">ob_size</tt> to indicate a | |
313 | negative number, and N is <code>abs(<tt class="member">ob_size</tt>)</code> there. Also, | |
314 | the presence of an <tt class="member">ob_size</tt> field in the instance layout | |
315 | doesn't mean that the instance structure is variable-length (for | |
316 | example, the structure for the list type has fixed-length instances, | |
317 | yet those instances have a meaningful <tt class="member">ob_size</tt> field). | |
318 | ||
319 | <P> | |
320 | The basic size includes the fields in the instance declared by the | |
321 | macro PyObject_HEAD or | |
322 | PyObject_VAR_HEAD (whichever is used to declare the | |
323 | instance struct) and this in turn includes the <tt class="member">_ob_prev</tt> and | |
324 | <tt class="member">_ob_next</tt> fields if they are present. This means that the | |
325 | only correct way to get an initializer for the <tt class="member">tp_basicsize</tt> | |
326 | is to use the <tt class="keyword">sizeof</tt> operator on the struct used to | |
327 | declare the instance layout. The basic size does not include the GC | |
328 | header size (this is new in Python 2.2; in 2.1 and 2.0, the GC | |
329 | header size was included in <tt class="member">tp_basicsize</tt>). | |
330 | ||
331 | <P> | |
332 | These fields are inherited separately by subtypes. If the base type | |
333 | has a non-zero <tt class="member">tp_itemsize</tt>, it is generally not safe to set | |
334 | <tt class="member">tp_itemsize</tt> to a different non-zero value in a subtype | |
335 | (though this depends on the implementation of the base type). | |
336 | ||
337 | <P> | |
338 | A note about alignment: if the variable items require a particular | |
339 | alignment, this should be taken care of by the value of | |
340 | <tt class="member">tp_basicsize</tt>. Example: suppose a type implements an array | |
341 | of <code>double</code>. <tt class="member">tp_itemsize</tt> is <code>sizeof(double)</code>. | |
342 | It is the programmer's responsibility that <tt class="member">tp_basicsize</tt> is | |
343 | a multiple of <code>sizeof(double)</code> (assuming this is the alignment | |
344 | requirement for <code>double</code>). | |
345 | </dl> | |
346 | ||
347 | <P> | |
348 | <dl><dt>destructor <b><tt id='l2h-943' xml:id='l2h-943' class="cmember">tp_dealloc</tt></b></dt> | |
349 | <dd> | |
350 | A pointer to the instance destructor function. This function must | |
351 | be defined unless the type guarantees that its instances will never | |
352 | be deallocated (as is the case for the singletons <code>None</code> and | |
353 | <code>Ellipsis</code>). | |
354 | ||
355 | <P> | |
356 | The destructor function is called by the <tt class="cfunction">Py_DECREF()</tt> and | |
357 | <tt class="cfunction">Py_XDECREF()</tt> macros when the new reference count is | |
358 | zero. At this point, the instance is still in existence, but there | |
359 | are no references to it. The destructor function should free all | |
360 | references which the instance owns, free all memory buffers owned by | |
361 | the instance (using the freeing function corresponding to the | |
362 | allocation function used to allocate the buffer), and finally (as | |
363 | its last action) call the type's <tt class="member">tp_free</tt> function. If the | |
364 | type is not subtypable (doesn't have the | |
365 | <tt class="constant">Py_TPFLAGS_BASETYPE</tt> flag bit set), it is permissible to | |
366 | call the object deallocator directly instead of via | |
367 | <tt class="member">tp_free</tt>. The object deallocator should be the one used to | |
368 | allocate the instance; this is normally <tt class="cfunction">PyObject_Del()</tt> | |
369 | if the instance was allocated using <tt class="cfunction">PyObject_New()</tt> or | |
370 | <tt class="cfunction">PyOject_VarNew()</tt>, or <tt class="cfunction">PyObject_GC_Del()</tt> if | |
371 | the instance was allocated using <tt class="cfunction">PyObject_GC_New()</tt> or | |
372 | <tt class="cfunction">PyObject_GC_VarNew()</tt>. | |
373 | ||
374 | <P> | |
375 | This field is inherited by subtypes. | |
376 | </dl> | |
377 | ||
378 | <P> | |
379 | <dl><dt>printfunc <b><tt id='l2h-944' xml:id='l2h-944' class="cmember">tp_print</tt></b></dt> | |
380 | <dd> | |
381 | An optional pointer to the instance print function. | |
382 | ||
383 | <P> | |
384 | The print function is only called when the instance is printed to a | |
385 | <em>real</em> file; when it is printed to a pseudo-file (like a | |
386 | <tt class="class">StringIO</tt> instance), the instance's <tt class="member">tp_repr</tt> or | |
387 | <tt class="member">tp_str</tt> function is called to convert it to a string. These | |
388 | are also called when the type's <tt class="member">tp_print</tt> field is <tt class="constant">NULL</tt>. A | |
389 | type should never implement <tt class="member">tp_print</tt> in a way that produces | |
390 | different output than <tt class="member">tp_repr</tt> or <tt class="member">tp_str</tt> would. | |
391 | ||
392 | <P> | |
393 | The print function is called with the same signature as | |
394 | <tt class="cfunction">PyObject_Print()</tt>: <code>int tp_print(PyObject *self, FILE | |
395 | *file, int flags)</code>. The <var>self</var> argument is the instance to be | |
396 | printed. The <var>file</var> argument is the stdio file to which it is | |
397 | to be printed. The <var>flags</var> argument is composed of flag bits. | |
398 | The only flag bit currently defined is <tt class="constant">Py_PRINT_RAW</tt>. | |
399 | When the <tt class="constant">Py_PRINT_RAW</tt> flag bit is set, the instance | |
400 | should be printed the same way as <tt class="member">tp_str</tt> would format it; | |
401 | when the <tt class="constant">Py_PRINT_RAW</tt> flag bit is clear, the instance | |
402 | should be printed the same was as <tt class="member">tp_repr</tt> would format it. | |
403 | It should return <code>-1</code> and set an exception condition when an | |
404 | error occurred during the comparison. | |
405 | ||
406 | <P> | |
407 | It is possible that the <tt class="member">tp_print</tt> field will be deprecated. | |
408 | In any case, it is recommended not to define <tt class="member">tp_print</tt>, but | |
409 | instead to rely on <tt class="member">tp_repr</tt> and <tt class="member">tp_str</tt> for | |
410 | printing. | |
411 | ||
412 | <P> | |
413 | This field is inherited by subtypes. | |
414 | </dl> | |
415 | ||
416 | <P> | |
417 | <dl><dt>getattrfunc <b><tt id='l2h-945' xml:id='l2h-945' class="cmember">tp_getattr</tt></b></dt> | |
418 | <dd> | |
419 | An optional pointer to the get-attribute-string function. | |
420 | ||
421 | <P> | |
422 | This field is deprecated. When it is defined, it should point to a | |
423 | function that acts the same as the <tt class="member">tp_getattro</tt> function, | |
424 | but taking a C string instead of a Python string object to give the | |
425 | attribute name. The signature is the same as for | |
426 | <tt class="cfunction">PyObject_GetAttrString()</tt>. | |
427 | ||
428 | <P> | |
429 | This field is inherited by subtypes together with | |
430 | <tt class="member">tp_getattro</tt>: a subtype inherits both <tt class="member">tp_getattr</tt> | |
431 | and <tt class="member">tp_getattro</tt> from its base type when the subtype's | |
432 | <tt class="member">tp_getattr</tt> and <tt class="member">tp_getattro</tt> are both <tt class="constant">NULL</tt>. | |
433 | </dl> | |
434 | ||
435 | <P> | |
436 | <dl><dt>setattrfunc <b><tt id='l2h-946' xml:id='l2h-946' class="cmember">tp_setattr</tt></b></dt> | |
437 | <dd> | |
438 | An optional pointer to the set-attribute-string function. | |
439 | ||
440 | <P> | |
441 | This field is deprecated. When it is defined, it should point to a | |
442 | function that acts the same as the <tt class="member">tp_setattro</tt> function, | |
443 | but taking a C string instead of a Python string object to give the | |
444 | attribute name. The signature is the same as for | |
445 | <tt class="cfunction">PyObject_SetAttrString()</tt>. | |
446 | ||
447 | <P> | |
448 | This field is inherited by subtypes together with | |
449 | <tt class="member">tp_setattro</tt>: a subtype inherits both <tt class="member">tp_setattr</tt> | |
450 | and <tt class="member">tp_setattro</tt> from its base type when the subtype's | |
451 | <tt class="member">tp_setattr</tt> and <tt class="member">tp_setattro</tt> are both <tt class="constant">NULL</tt>. | |
452 | </dl> | |
453 | ||
454 | <P> | |
455 | <dl><dt>cmpfunc <b><tt id='l2h-947' xml:id='l2h-947' class="cmember">tp_compare</tt></b></dt> | |
456 | <dd> | |
457 | An optional pointer to the three-way comparison function. | |
458 | ||
459 | <P> | |
460 | The signature is the same as for <tt class="cfunction">PyObject_Compare()</tt>. | |
461 | The function should return <code>1</code> if <var>self</var> greater than | |
462 | <var>other</var>, <code>0</code> if <var>self</var> is equal to <var>other</var>, and | |
463 | <code>-1</code> if <var>self</var> less than <var>other</var>. It should return | |
464 | <code>-1</code> and set an exception condition when an error occurred | |
465 | during the comparison. | |
466 | ||
467 | <P> | |
468 | This field is inherited by subtypes together with | |
469 | <tt class="member">tp_richcompare</tt> and <tt class="member">tp_hash</tt>: a subtypes inherits | |
470 | all three of <tt class="member">tp_compare</tt>, <tt class="member">tp_richcompare</tt>, and | |
471 | <tt class="member">tp_hash</tt> when the subtype's <tt class="member">tp_compare</tt>, | |
472 | <tt class="member">tp_richcompare</tt>, and <tt class="member">tp_hash</tt> are all <tt class="constant">NULL</tt>. | |
473 | </dl> | |
474 | ||
475 | <P> | |
476 | <dl><dt>reprfunc <b><tt id='l2h-948' xml:id='l2h-948' class="cmember">tp_repr</tt></b></dt> | |
477 | <dd> | |
478 | An optional pointer to a function that implements the built-in | |
479 | function <tt class="function">repr()</tt>.<a id='l2h-949' xml:id='l2h-949'></a> | |
480 | <P> | |
481 | The signature is the same as for <tt class="cfunction">PyObject_Repr()</tt>; it | |
482 | must return a string or a Unicode object. Ideally, this function | |
483 | should return a string that, when passed to <tt class="function">eval()</tt>, given | |
484 | a suitable environment, returns an object with the same value. If | |
485 | this is not feasible, it should return a string starting with | |
486 | "<tt class="character"><</tt>" and ending with "<tt class="character">></tt>" from | |
487 | which both the type and the value of the object can be deduced. | |
488 | ||
489 | <P> | |
490 | When this field is not set, a string of the form "<tt class="samp"><%s object | |
491 | at %p></tt>" is returned, where <code>%s</code> is replaced by the type name, | |
492 | and <code>%p</code> by the object's memory address. | |
493 | ||
494 | <P> | |
495 | This field is inherited by subtypes. | |
496 | </dl> | |
497 | ||
498 | <P> | |
499 | PyNumberMethods *tp_as_number; | |
500 | ||
501 | <P> | |
502 | XXX | |
503 | ||
504 | <P> | |
505 | PySequenceMethods *tp_as_sequence; | |
506 | ||
507 | <P> | |
508 | XXX | |
509 | ||
510 | <P> | |
511 | PyMappingMethods *tp_as_mapping; | |
512 | ||
513 | <P> | |
514 | XXX | |
515 | ||
516 | <P> | |
517 | <dl><dt>hashfunc <b><tt id='l2h-950' xml:id='l2h-950' class="cmember">tp_hash</tt></b></dt> | |
518 | <dd> | |
519 | An optional pointer to a function that implements the built-in | |
520 | function <tt class="function">hash()</tt>.<a id='l2h-951' xml:id='l2h-951'></a> | |
521 | <P> | |
522 | The signature is the same as for <tt class="cfunction">PyObject_Hash()</tt>; it | |
523 | must return a C long. The value <code>-1</code> should not be returned as | |
524 | a normal return value; when an error occurs during the computation | |
525 | of the hash value, the function should set an exception and return | |
526 | <code>-1</code>. | |
527 | ||
528 | <P> | |
529 | When this field is not set, two possibilities exist: if the | |
530 | <tt class="member">tp_compare</tt> and <tt class="member">tp_richcompare</tt> fields are both | |
531 | <tt class="constant">NULL</tt>, a default hash value based on the object's address is | |
532 | returned; otherwise, a <tt class="exception">TypeError</tt> is raised. | |
533 | ||
534 | <P> | |
535 | This field is inherited by subtypes together with | |
536 | <tt class="member">tp_richcompare</tt> and <tt class="member">tp_compare</tt>: a subtypes inherits | |
537 | all three of <tt class="member">tp_compare</tt>, <tt class="member">tp_richcompare</tt>, and | |
538 | <tt class="member">tp_hash</tt>, when the subtype's <tt class="member">tp_compare</tt>, | |
539 | <tt class="member">tp_richcompare</tt> and <tt class="member">tp_hash</tt> are all <tt class="constant">NULL</tt>. | |
540 | </dl> | |
541 | ||
542 | <P> | |
543 | <dl><dt>ternaryfunc <b><tt id='l2h-952' xml:id='l2h-952' class="cmember">tp_call</tt></b></dt> | |
544 | <dd> | |
545 | An optional pointer to a function that implements calling the | |
546 | object. This should be <tt class="constant">NULL</tt> if the object is not callable. The | |
547 | signature is the same as for <tt class="cfunction">PyObject_Call()</tt>. | |
548 | ||
549 | <P> | |
550 | This field is inherited by subtypes. | |
551 | </dl> | |
552 | ||
553 | <P> | |
554 | <dl><dt>reprfunc <b><tt id='l2h-953' xml:id='l2h-953' class="cmember">tp_str</tt></b></dt> | |
555 | <dd> | |
556 | An optional pointer to a function that implements the built-in | |
557 | operation <tt class="function">str()</tt>. (Note that <tt class="class">str</tt> is a type now, | |
558 | and <tt class="function">str()</tt> calls the constructor for that type. This | |
559 | constructor calls <tt class="cfunction">PyObject_Str()</tt> to do the actual work, | |
560 | and <tt class="cfunction">PyObject_Str()</tt> will call this handler.) | |
561 | ||
562 | <P> | |
563 | The signature is the same as for <tt class="cfunction">PyObject_Str()</tt>; it must | |
564 | return a string or a Unicode object. This function should return a | |
565 | ``friendly'' string representation of the object, as this is the | |
566 | representation that will be used by the print statement. | |
567 | ||
568 | <P> | |
569 | When this field is not set, <tt class="cfunction">PyObject_Repr()</tt> is called to | |
570 | return a string representation. | |
571 | ||
572 | <P> | |
573 | This field is inherited by subtypes. | |
574 | </dl> | |
575 | ||
576 | <P> | |
577 | <dl><dt>getattrofunc <b><tt id='l2h-954' xml:id='l2h-954' class="cmember">tp_getattro</tt></b></dt> | |
578 | <dd> | |
579 | An optional pointer to the get-attribute function. | |
580 | ||
581 | <P> | |
582 | The signature is the same as for <tt class="cfunction">PyObject_GetAttr()</tt>. It | |
583 | is usually convenient to set this field to | |
584 | <tt class="cfunction">PyObject_GenericGetAttr()</tt>, which implements the normal | |
585 | way of looking for object attributes. | |
586 | ||
587 | <P> | |
588 | This field is inherited by subtypes together with | |
589 | <tt class="member">tp_getattr</tt>: a subtype inherits both <tt class="member">tp_getattr</tt> and | |
590 | <tt class="member">tp_getattro</tt> from its base type when the subtype's | |
591 | <tt class="member">tp_getattr</tt> and <tt class="member">tp_getattro</tt> are both <tt class="constant">NULL</tt>. | |
592 | </dl> | |
593 | ||
594 | <P> | |
595 | <dl><dt>setattrofunc <b><tt id='l2h-955' xml:id='l2h-955' class="cmember">tp_setattro</tt></b></dt> | |
596 | <dd> | |
597 | An optional pointer to the set-attribute function. | |
598 | ||
599 | <P> | |
600 | The signature is the same as for <tt class="cfunction">PyObject_SetAttr()</tt>. It | |
601 | is usually convenient to set this field to | |
602 | <tt class="cfunction">PyObject_GenericSetAttr()</tt>, which implements the normal | |
603 | way of setting object attributes. | |
604 | ||
605 | <P> | |
606 | This field is inherited by subtypes together with | |
607 | <tt class="member">tp_setattr</tt>: a subtype inherits both <tt class="member">tp_setattr</tt> and | |
608 | <tt class="member">tp_setattro</tt> from its base type when the subtype's | |
609 | <tt class="member">tp_setattr</tt> and <tt class="member">tp_setattro</tt> are both <tt class="constant">NULL</tt>. | |
610 | </dl> | |
611 | ||
612 | <P> | |
613 | <dl><dt>PyBufferProcs* <b><tt id='l2h-956' xml:id='l2h-956' class="cmember">tp_as_buffer</tt></b></dt> | |
614 | <dd> | |
615 | Pointer to an additional structure that contains fields relevant only to | |
616 | objects which implement the buffer interface. These fields are | |
617 | documented in ``Buffer Object Structures'' (section | |
618 | <A href="buffer-structs.html#buffer-structs">10.7</A>). | |
619 | ||
620 | <P> | |
621 | The <tt class="member">tp_as_buffer</tt> field is not inherited, but the contained | |
622 | fields are inherited individually. | |
623 | </dl> | |
624 | ||
625 | <P> | |
626 | <dl><dt>long <b><tt id='l2h-957' xml:id='l2h-957' class="cmember">tp_flags</tt></b></dt> | |
627 | <dd> | |
628 | This field is a bit mask of various flags. Some flags indicate | |
629 | variant semantics for certain situations; others are used to | |
630 | indicate that certain fields in the type object (or in the extension | |
631 | structures referenced via <tt class="member">tp_as_number</tt>, | |
632 | <tt class="member">tp_as_sequence</tt>, <tt class="member">tp_as_mapping</tt>, and | |
633 | <tt class="member">tp_as_buffer</tt>) that were historically not always present are | |
634 | valid; if such a flag bit is clear, the type fields it guards must | |
635 | not be accessed and must be considered to have a zero or <tt class="constant">NULL</tt> | |
636 | value instead. | |
637 | ||
638 | <P> | |
639 | Inheritance of this field is complicated. Most flag bits are | |
640 | inherited individually, i.e. if the base type has a flag bit set, | |
641 | the subtype inherits this flag bit. The flag bits that pertain to | |
642 | extension structures are strictly inherited if the extension | |
643 | structure is inherited, i.e. the base type's value of the flag bit | |
644 | is copied into the subtype together with a pointer to the extension | |
645 | structure. The <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit is inherited | |
646 | together with the <tt class="member">tp_traverse</tt> and <tt class="member">tp_clear</tt> fields, | |
647 | i.e. if the <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit is clear in the | |
648 | subtype and the <tt class="member">tp_traverse</tt> and <tt class="member">tp_clear</tt> fields in | |
649 | the subtype exist (as indicated by the | |
650 | <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt> flag bit) and have <tt class="constant">NULL</tt> | |
651 | values. | |
652 | ||
653 | <P> | |
654 | The following bit masks are currently defined; these can be or-ed | |
655 | together using the <code>|</code> operator to form the value of the | |
656 | <tt class="member">tp_flags</tt> field. The macro <tt class="cfunction">PyType_HasFeature()</tt> | |
657 | takes a type and a flags value, <var>tp</var> and <var>f</var>, and checks | |
658 | whether <code><var>tp</var>->tp_flags & <var>f</var></code> is non-zero. | |
659 | ||
660 | <P> | |
661 | <dl><dt><b><tt id='l2h-958' xml:id='l2h-958'>Py_TPFLAGS_HAVE_GETCHARBUFFER</tt></b></dt> | |
662 | <dd> | |
663 | If this bit is set, the <tt class="ctype">PyBufferProcs</tt> struct referenced by | |
664 | <tt class="member">tp_as_buffer</tt> has the <tt class="member">bf_getcharbuffer</tt> field. | |
665 | </dd></dl> | |
666 | ||
667 | <P> | |
668 | <dl><dt><b><tt id='l2h-959' xml:id='l2h-959'>Py_TPFLAGS_HAVE_SEQUENCE_IN</tt></b></dt> | |
669 | <dd> | |
670 | If this bit is set, the <tt class="ctype">PySequenceMethods</tt> struct | |
671 | referenced by <tt class="member">tp_as_sequence</tt> has the <tt class="member">sq_contains</tt> | |
672 | field. | |
673 | </dd></dl> | |
674 | ||
675 | <P> | |
676 | <dl><dt><b><tt id='l2h-960' xml:id='l2h-960'>Py_TPFLAGS_GC</tt></b></dt> | |
677 | <dd> | |
678 | This bit is obsolete. The bit it used to name is no longer in | |
679 | use. The symbol is now defined as zero. | |
680 | </dd></dl> | |
681 | ||
682 | <P> | |
683 | <dl><dt><b><tt id='l2h-961' xml:id='l2h-961'>Py_TPFLAGS_HAVE_INPLACEOPS</tt></b></dt> | |
684 | <dd> | |
685 | If this bit is set, the <tt class="ctype">PySequenceMethods</tt> struct | |
686 | referenced by <tt class="member">tp_as_sequence</tt> and the | |
687 | <tt class="ctype">PyNumberMethods</tt> structure referenced by | |
688 | <tt class="member">tp_as_number</tt> contain the fields for in-place operators. | |
689 | In particular, this means that the <tt class="ctype">PyNumberMethods</tt> | |
690 | structure has the fields <tt class="member">nb_inplace_add</tt>, | |
691 | <tt class="member">nb_inplace_subtract</tt>, <tt class="member">nb_inplace_multiply</tt>, | |
692 | <tt class="member">nb_inplace_divide</tt>, <tt class="member">nb_inplace_remainder</tt>, | |
693 | <tt class="member">nb_inplace_power</tt>, <tt class="member">nb_inplace_lshift</tt>, | |
694 | <tt class="member">nb_inplace_rshift</tt>, <tt class="member">nb_inplace_and</tt>, | |
695 | <tt class="member">nb_inplace_xor</tt>, and <tt class="member">nb_inplace_or</tt>; and the | |
696 | <tt class="ctype">PySequenceMethods</tt> struct has the fields | |
697 | <tt class="member">sq_inplace_concat</tt> and <tt class="member">sq_inplace_repeat</tt>. | |
698 | </dd></dl> | |
699 | ||
700 | <P> | |
701 | <dl><dt><b><tt id='l2h-962' xml:id='l2h-962'>Py_TPFLAGS_CHECKTYPES</tt></b></dt> | |
702 | <dd> | |
703 | If this bit is set, the binary and ternary operations in the | |
704 | <tt class="ctype">PyNumberMethods</tt> structure referenced by | |
705 | <tt class="member">tp_as_number</tt> accept arguments of arbitrary object types, | |
706 | and do their own type conversions if needed. If this bit is | |
707 | clear, those operations require that all arguments have the | |
708 | current type as their type, and the caller is supposed to perform | |
709 | a coercion operation first. This applies to <tt class="member">nb_add</tt>, | |
710 | <tt class="member">nb_subtract</tt>, <tt class="member">nb_multiply</tt>, <tt class="member">nb_divide</tt>, | |
711 | <tt class="member">nb_remainder</tt>, <tt class="member">nb_divmod</tt>, <tt class="member">nb_power</tt>, | |
712 | <tt class="member">nb_lshift</tt>, <tt class="member">nb_rshift</tt>, <tt class="member">nb_and</tt>, | |
713 | <tt class="member">nb_xor</tt>, and <tt class="member">nb_or</tt>. | |
714 | </dd></dl> | |
715 | ||
716 | <P> | |
717 | <dl><dt><b><tt id='l2h-963' xml:id='l2h-963'>Py_TPFLAGS_HAVE_RICHCOMPARE</tt></b></dt> | |
718 | <dd> | |
719 | If this bit is set, the type object has the | |
720 | <tt class="member">tp_richcompare</tt> field, as well as the <tt class="member">tp_traverse</tt> | |
721 | and the <tt class="member">tp_clear</tt> fields. | |
722 | </dd></dl> | |
723 | ||
724 | <P> | |
725 | <dl><dt><b><tt id='l2h-964' xml:id='l2h-964'>Py_TPFLAGS_HAVE_WEAKREFS</tt></b></dt> | |
726 | <dd> | |
727 | If this bit is set, the <tt class="member">tp_weaklistoffset</tt> field is | |
728 | defined. Instances of a type are weakly referenceable if the | |
729 | type's <tt class="member">tp_weaklistoffset</tt> field has a value greater than | |
730 | zero. | |
731 | </dd></dl> | |
732 | ||
733 | <P> | |
734 | <dl><dt><b><tt id='l2h-965' xml:id='l2h-965'>Py_TPFLAGS_HAVE_ITER</tt></b></dt> | |
735 | <dd> | |
736 | If this bit is set, the type object has the <tt class="member">tp_iter</tt> and | |
737 | <tt class="member">tp_iternext</tt> fields. | |
738 | </dd></dl> | |
739 | ||
740 | <P> | |
741 | <dl><dt><b><tt id='l2h-966' xml:id='l2h-966'>Py_TPFLAGS_HAVE_CLASS</tt></b></dt> | |
742 | <dd> | |
743 | If this bit is set, the type object has several new fields defined | |
744 | starting in Python 2.2: <tt class="member">tp_methods</tt>, <tt class="member">tp_members</tt>, | |
745 | <tt class="member">tp_getset</tt>, <tt class="member">tp_base</tt>, <tt class="member">tp_dict</tt>, | |
746 | <tt class="member">tp_descr_get</tt>, <tt class="member">tp_descr_set</tt>, | |
747 | <tt class="member">tp_dictoffset</tt>, <tt class="member">tp_init</tt>, <tt class="member">tp_alloc</tt>, | |
748 | <tt class="member">tp_new</tt>, <tt class="member">tp_free</tt>, <tt class="member">tp_is_gc</tt>, | |
749 | <tt class="member">tp_bases</tt>, <tt class="member">tp_mro</tt>, <tt class="member">tp_cache</tt>, | |
750 | <tt class="member">tp_subclasses</tt>, and <tt class="member">tp_weaklist</tt>. | |
751 | </dd></dl> | |
752 | ||
753 | <P> | |
754 | <dl><dt><b><tt id='l2h-967' xml:id='l2h-967'>Py_TPFLAGS_HEAPTYPE</tt></b></dt> | |
755 | <dd> | |
756 | This bit is set when the type object itself is allocated on the | |
757 | heap. In this case, the <tt class="member">ob_type</tt> field of its instances | |
758 | is considered a reference to the type, and the type object is | |
759 | INCREF'ed when a new instance is created, and DECREF'ed when an | |
760 | instance is destroyed (this does not apply to instances of | |
761 | subtypes; only the type referenced by the instance's ob_type gets | |
762 | INCREF'ed or DECREF'ed). | |
763 | </dd></dl> | |
764 | ||
765 | <P> | |
766 | <dl><dt><b><tt id='l2h-968' xml:id='l2h-968'>Py_TPFLAGS_BASETYPE</tt></b></dt> | |
767 | <dd> | |
768 | This bit is set when the type can be used as the base type of | |
769 | another type. If this bit is clear, the type cannot be subtyped | |
770 | (similar to a "final" class in Java). | |
771 | </dd></dl> | |
772 | ||
773 | <P> | |
774 | <dl><dt><b><tt id='l2h-969' xml:id='l2h-969'>Py_TPFLAGS_READY</tt></b></dt> | |
775 | <dd> | |
776 | This bit is set when the type object has been fully initialized by | |
777 | <tt class="cfunction">PyType_Ready()</tt>. | |
778 | </dd></dl> | |
779 | ||
780 | <P> | |
781 | <dl><dt><b><tt id='l2h-970' xml:id='l2h-970'>Py_TPFLAGS_READYING</tt></b></dt> | |
782 | <dd> | |
783 | This bit is set while <tt class="cfunction">PyType_Ready()</tt> is in the process | |
784 | of initializing the type object. | |
785 | </dd></dl> | |
786 | ||
787 | <P> | |
788 | <dl><dt><b><tt id='l2h-971' xml:id='l2h-971'>Py_TPFLAGS_HAVE_GC</tt></b></dt> | |
789 | <dd> | |
790 | This bit is set when the object supports garbage collection. If | |
791 | this bit is set, instances must be created using | |
792 | <tt class="cfunction">PyObject_GC_New()</tt> and destroyed using | |
793 | <tt class="cfunction">PyObject_GC_Del()</tt>. More information in section XXX | |
794 | about garbage collection. This bit also implies that the | |
795 | GC-related fields <tt class="member">tp_traverse</tt> and <tt class="member">tp_clear</tt> are | |
796 | present in the type object; but those fields also exist when | |
797 | <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> is clear but | |
798 | <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt> is set. | |
799 | </dd></dl> | |
800 | ||
801 | <P> | |
802 | <dl><dt><b><tt id='l2h-972' xml:id='l2h-972'>Py_TPFLAGS_DEFAULT</tt></b></dt> | |
803 | <dd> | |
804 | This is a bitmask of all the bits that pertain to the existence of | |
805 | certain fields in the type object and its extension structures. | |
806 | Currently, it includes the following bits: | |
807 | <tt class="constant">Py_TPFLAGS_HAVE_GETCHARBUFFER</tt>, | |
808 | <tt class="constant">Py_TPFLAGS_HAVE_SEQUENCE_IN</tt>, | |
809 | <tt class="constant">Py_TPFLAGS_HAVE_INPLACEOPS</tt>, | |
810 | <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt>, | |
811 | <tt class="constant">Py_TPFLAGS_HAVE_WEAKREFS</tt>, | |
812 | <tt class="constant">Py_TPFLAGS_HAVE_ITER</tt>, and | |
813 | <tt class="constant">Py_TPFLAGS_HAVE_CLASS</tt>. | |
814 | </dd></dl> | |
815 | </dl> | |
816 | ||
817 | <P> | |
818 | <dl><dt>char* <b><tt id='l2h-973' xml:id='l2h-973' class="cmember">tp_doc</tt></b></dt> | |
819 | <dd> | |
820 | An optional pointer to a NUL-terminated C string giving the | |
821 | docstring for this type object. This is exposed as the | |
822 | <tt class="member">__doc__</tt> attribute on the type and instances of the type. | |
823 | ||
824 | <P> | |
825 | This field is <em>not</em> inherited by subtypes. | |
826 | </dl> | |
827 | ||
828 | <P> | |
829 | The following three fields only exist if the | |
830 | <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt> flag bit is set. | |
831 | ||
832 | <P> | |
833 | <dl><dt>traverseproc <b><tt id='l2h-974' xml:id='l2h-974' class="cmember">tp_traverse</tt></b></dt> | |
834 | <dd> | |
835 | An optional pointer to a traversal function for the garbage | |
836 | collector. This is only used if the <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> | |
837 | flag bit is set. More information in section | |
838 | <A href="supporting-cycle-detection.html#supporting-cycle-detection">10.9</A> about garbage collection. | |
839 | ||
840 | <P> | |
841 | This field is inherited by subtypes together with <tt class="member">tp_clear</tt> | |
842 | and the <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit: the flag bit, | |
843 | <tt class="member">tp_traverse</tt>, and <tt class="member">tp_clear</tt> are all inherited from | |
844 | the base type if they are all zero in the subtype <em>and</em> the | |
845 | subtype has the <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt> flag bit set. | |
846 | </dl> | |
847 | ||
848 | <P> | |
849 | <dl><dt>inquiry <b><tt id='l2h-975' xml:id='l2h-975' class="cmember">tp_clear</tt></b></dt> | |
850 | <dd> | |
851 | An optional pointer to a clear function for the garbage collector. | |
852 | This is only used if the <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit is | |
853 | set. More information in section | |
854 | <A href="supporting-cycle-detection.html#supporting-cycle-detection">10.9</A> about garbage collection. | |
855 | ||
856 | <P> | |
857 | This field is inherited by subtypes together with <tt class="member">tp_clear</tt> | |
858 | and the <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit: the flag bit, | |
859 | <tt class="member">tp_traverse</tt>, and <tt class="member">tp_clear</tt> are all inherited from | |
860 | the base type if they are all zero in the subtype <em>and</em> the | |
861 | subtype has the <tt class="constant">Py_TPFLAGS_HAVE_RICHCOMPARE</tt> flag bit set. | |
862 | </dl> | |
863 | ||
864 | <P> | |
865 | <dl><dt>richcmpfunc <b><tt id='l2h-976' xml:id='l2h-976' class="cmember">tp_richcompare</tt></b></dt> | |
866 | <dd> | |
867 | An optional pointer to the rich comparison function. | |
868 | ||
869 | <P> | |
870 | The signature is the same as for <tt class="cfunction">PyObject_RichCompare()</tt>. | |
871 | The function should return <code>1</code> if the requested comparison | |
872 | returns true, <code>0</code> if it returns false. It should return | |
873 | <code>-1</code> and set an exception condition when an error occurred | |
874 | during the comparison. | |
875 | ||
876 | <P> | |
877 | This field is inherited by subtypes together with | |
878 | <tt class="member">tp_compare</tt> and <tt class="member">tp_hash</tt>: a subtype inherits all | |
879 | three of <tt class="member">tp_compare</tt>, <tt class="member">tp_richcompare</tt>, and | |
880 | <tt class="member">tp_hash</tt>, when the subtype's <tt class="member">tp_compare</tt>, | |
881 | <tt class="member">tp_richcompare</tt>, and <tt class="member">tp_hash</tt> are all <tt class="constant">NULL</tt>. | |
882 | ||
883 | <P> | |
884 | The following constants are defined to be used as the third argument | |
885 | for <tt class="member">tp_richcompare</tt> and for <tt class="cfunction">PyObject_RichCompare()</tt>: | |
886 | ||
887 | <P> | |
888 | <div class="center"><table class="realtable"> | |
889 | <thead> | |
890 | <tr> | |
891 | <th class="left" >Constant</th> | |
892 | <th class="center">Comparison</th> | |
893 | </tr> | |
894 | </thead> | |
895 | <tbody> | |
896 | <tr><td class="left" valign="baseline"><tt class="constant">Py_LT</tt></td> | |
897 | <td class="center"><code><</code></td></tr> | |
898 | <tr><td class="left" valign="baseline"><tt class="constant">Py_LE</tt></td> | |
899 | <td class="center"><code><=</code></td></tr> | |
900 | <tr><td class="left" valign="baseline"><tt class="constant">Py_EQ</tt></td> | |
901 | <td class="center"><code>==</code></td></tr> | |
902 | <tr><td class="left" valign="baseline"><tt class="constant">Py_NE</tt></td> | |
903 | <td class="center"><code>!=</code></td></tr> | |
904 | <tr><td class="left" valign="baseline"><tt class="constant">Py_GT</tt></td> | |
905 | <td class="center"><code>></code></td></tr> | |
906 | <tr><td class="left" valign="baseline"><tt class="constant">Py_GE</tt></td> | |
907 | <td class="center"><code>>=</code></td></tr></tbody> | |
908 | </table></div> | |
909 | </dl> | |
910 | ||
911 | <P> | |
912 | The next field only exists if the <tt class="constant">Py_TPFLAGS_HAVE_WEAKREFS</tt> | |
913 | flag bit is set. | |
914 | ||
915 | <P> | |
916 | <dl><dt>long <b><tt id='l2h-977' xml:id='l2h-977' class="cmember">tp_weaklistoffset</tt></b></dt> | |
917 | <dd> | |
918 | If the instances of this type are weakly referenceable, this field | |
919 | is greater than zero and contains the offset in the instance | |
920 | structure of the weak reference list head (ignoring the GC header, | |
921 | if present); this offset is used by | |
922 | <tt class="cfunction">PyObject_ClearWeakRefs()</tt> and the | |
923 | <tt class="cfunction">PyWeakref_*()</tt> functions. The instance structure needs | |
924 | to include a field of type <tt class="ctype">PyObject*</tt> which is initialized to | |
925 | <tt class="constant">NULL</tt>. | |
926 | ||
927 | <P> | |
928 | Do not confuse this field with <tt class="member">tp_weaklist</tt>; that is the | |
929 | list head for weak references to the type object itself. | |
930 | ||
931 | <P> | |
932 | This field is inherited by subtypes, but see the rules listed below. | |
933 | A subtype may override this offset; this means that the subtype uses | |
934 | a different weak reference list head than the base type. Since the | |
935 | list head is always found via <tt class="member">tp_weaklistoffset</tt>, this | |
936 | should not be a problem. | |
937 | ||
938 | <P> | |
939 | When a type defined by a class statement has no <tt class="member">__slots__</tt> | |
940 | declaration, and none of its base types are weakly referenceable, | |
941 | the type is made weakly referenceable by adding a weak reference | |
942 | list head slot to the instance layout and setting the | |
943 | <tt class="member">tp_weaklistoffset</tt> of that slot's offset. | |
944 | ||
945 | <P> | |
946 | When a type's <tt class="member">__slots__</tt> declaration contains a slot named | |
947 | <tt class="member">__weakref__</tt>, that slot becomes the weak reference list head | |
948 | for instances of the type, and the slot's offset is stored in the | |
949 | type's <tt class="member">tp_weaklistoffset</tt>. | |
950 | ||
951 | <P> | |
952 | When a type's <tt class="member">__slots__</tt> declaration does not contain a slot | |
953 | named <tt class="member">__weakref__</tt>, the type inherits its | |
954 | <tt class="member">tp_weaklistoffset</tt> from its base type. | |
955 | </dl> | |
956 | ||
957 | <P> | |
958 | The next two fields only exist if the | |
959 | <tt class="constant">Py_TPFLAGS_HAVE_CLASS</tt> flag bit is set. | |
960 | ||
961 | <P> | |
962 | <dl><dt>getiterfunc <b><tt id='l2h-978' xml:id='l2h-978' class="cmember">tp_iter</tt></b></dt> | |
963 | <dd> | |
964 | An optional pointer to a function that returns an iterator for the | |
965 | object. Its presence normally signals that the instances of this | |
966 | type are iterable (although sequences may be iterable without this | |
967 | function, and classic instances always have this function, even if | |
968 | they don't define an <tt class="method">__iter__()</tt> method). | |
969 | ||
970 | <P> | |
971 | This function has the same signature as | |
972 | <tt class="cfunction">PyObject_GetIter()</tt>. | |
973 | ||
974 | <P> | |
975 | This field is inherited by subtypes. | |
976 | </dl> | |
977 | ||
978 | <P> | |
979 | <dl><dt>iternextfunc <b><tt id='l2h-979' xml:id='l2h-979' class="cmember">tp_iternext</tt></b></dt> | |
980 | <dd> | |
981 | An optional pointer to a function that returns the next item in an | |
982 | iterator, or raises <tt class="exception">StopIteration</tt> when the iterator is | |
983 | exhausted. Its presence normally signals that the instances of this | |
984 | type are iterators (although classic instances always have this | |
985 | function, even if they don't define a <tt class="method">next()</tt> method). | |
986 | ||
987 | <P> | |
988 | Iterator types should also define the <tt class="member">tp_iter</tt> function, and | |
989 | that function should return the iterator instance itself (not a new | |
990 | iterator instance). | |
991 | ||
992 | <P> | |
993 | This function has the same signature as <tt class="cfunction">PyIter_Next()</tt>. | |
994 | ||
995 | <P> | |
996 | This field is inherited by subtypes. | |
997 | </dl> | |
998 | ||
999 | <P> | |
1000 | The next fields, up to and including <tt class="member">tp_weaklist</tt>, only exist | |
1001 | if the <tt class="constant">Py_TPFLAGS_HAVE_CLASS</tt> flag bit is set. | |
1002 | ||
1003 | <P> | |
1004 | <dl><dt>struct PyMethodDef* <b><tt id='l2h-980' xml:id='l2h-980' class="cmember">tp_methods</tt></b></dt> | |
1005 | <dd> | |
1006 | An optional pointer to a static <tt class="constant">NULL</tt>-terminated array of | |
1007 | <tt class="ctype">PyMethodDef</tt> structures, declaring regular methods of this | |
1008 | type. | |
1009 | ||
1010 | <P> | |
1011 | For each entry in the array, an entry is added to the type's | |
1012 | dictionary (see <tt class="member">tp_dict</tt> below) containing a method | |
1013 | descriptor. | |
1014 | ||
1015 | <P> | |
1016 | This field is not inherited by subtypes (methods are | |
1017 | inherited through a different mechanism). | |
1018 | </dl> | |
1019 | ||
1020 | <P> | |
1021 | <dl><dt>struct PyMemberDef* <b><tt id='l2h-981' xml:id='l2h-981' class="cmember">tp_members</tt></b></dt> | |
1022 | <dd> | |
1023 | An optional pointer to a static <tt class="constant">NULL</tt>-terminated array of | |
1024 | <tt class="ctype">PyMemberDef</tt> structures, declaring regular data members | |
1025 | (fields or slots) of instances of this type. | |
1026 | ||
1027 | <P> | |
1028 | For each entry in the array, an entry is added to the type's | |
1029 | dictionary (see <tt class="member">tp_dict</tt> below) containing a member | |
1030 | descriptor. | |
1031 | ||
1032 | <P> | |
1033 | This field is not inherited by subtypes (members are inherited | |
1034 | through a different mechanism). | |
1035 | </dl> | |
1036 | ||
1037 | <P> | |
1038 | <dl><dt>struct PyGetSetDef* <b><tt id='l2h-982' xml:id='l2h-982' class="cmember">tp_getset</tt></b></dt> | |
1039 | <dd> | |
1040 | An optional pointer to a static <tt class="constant">NULL</tt>-terminated array of | |
1041 | <tt class="ctype">PyGetSetDef</tt> structures, declaring computed attributes of | |
1042 | instances of this type. | |
1043 | ||
1044 | <P> | |
1045 | For each entry in the array, an entry is added to the type's | |
1046 | dictionary (see <tt class="member">tp_dict</tt> below) containing a getset | |
1047 | descriptor. | |
1048 | ||
1049 | <P> | |
1050 | This field is not inherited by subtypes (computed attributes are | |
1051 | inherited through a different mechanism). | |
1052 | ||
1053 | <P> | |
1054 | Docs for PyGetSetDef (XXX belong elsewhere): | |
1055 | ||
1056 | <P> | |
1057 | <div class="verbatim"><pre> | |
1058 | typedef PyObject *(*getter)(PyObject *, void *); | |
1059 | typedef int (*setter)(PyObject *, PyObject *, void *); | |
1060 | ||
1061 | typedef struct PyGetSetDef { | |
1062 | char *name; /* attribute name */ | |
1063 | getter get; /* C function to get the attribute */ | |
1064 | setter set; /* C function to set the attribute */ | |
1065 | char *doc; /* optional doc string */ | |
1066 | void *closure; /* optional additional data for getter and setter */ | |
1067 | } PyGetSetDef; | |
1068 | </pre></div> | |
1069 | </dl> | |
1070 | ||
1071 | <P> | |
1072 | <dl><dt>PyTypeObject* <b><tt id='l2h-983' xml:id='l2h-983' class="cmember">tp_base</tt></b></dt> | |
1073 | <dd> | |
1074 | An optional pointer to a base type from which type properties are | |
1075 | inherited. At this level, only single inheritance is supported; | |
1076 | multiple inheritance require dynamically creating a type object by | |
1077 | calling the metatype. | |
1078 | ||
1079 | <P> | |
1080 | This field is not inherited by subtypes (obviously), but it defaults | |
1081 | to <code>&PyBaseObject_Type</code> (which to Python programmers is known | |
1082 | as the type <tt class="class">object</tt>). | |
1083 | </dl> | |
1084 | ||
1085 | <P> | |
1086 | <dl><dt>PyObject* <b><tt id='l2h-984' xml:id='l2h-984' class="cmember">tp_dict</tt></b></dt> | |
1087 | <dd> | |
1088 | The type's dictionary is stored here by <tt class="cfunction">PyType_Ready()</tt>. | |
1089 | ||
1090 | <P> | |
1091 | This field should normally be initialized to <tt class="constant">NULL</tt> before | |
1092 | PyType_Ready is called; it may also be initialized to a dictionary | |
1093 | containing initial attributes for the type. Once | |
1094 | <tt class="cfunction">PyType_Ready()</tt> has initialized the type, extra | |
1095 | attributes for the type may be added to this dictionary only if they | |
1096 | don't correspond to overloaded operations (like <tt class="method">__add__()</tt>). | |
1097 | ||
1098 | <P> | |
1099 | This field is not inherited by subtypes (though the attributes | |
1100 | defined in here are inherited through a different mechanism). | |
1101 | </dl> | |
1102 | ||
1103 | <P> | |
1104 | <dl><dt>descrgetfunc <b><tt id='l2h-985' xml:id='l2h-985' class="cmember">tp_descr_get</tt></b></dt> | |
1105 | <dd> | |
1106 | An optional pointer to a "descriptor get" function. | |
1107 | ||
1108 | <P> | |
1109 | XXX blah, blah. | |
1110 | ||
1111 | <P> | |
1112 | This field is inherited by subtypes. | |
1113 | </dl> | |
1114 | ||
1115 | <P> | |
1116 | <dl><dt>descrsetfunc <b><tt id='l2h-986' xml:id='l2h-986' class="cmember">tp_descr_set</tt></b></dt> | |
1117 | <dd> | |
1118 | An optional pointer to a "descriptor set" function. | |
1119 | ||
1120 | <P> | |
1121 | XXX blah, blah. | |
1122 | ||
1123 | <P> | |
1124 | This field is inherited by subtypes. | |
1125 | </dl> | |
1126 | ||
1127 | <P> | |
1128 | <dl><dt>long <b><tt id='l2h-987' xml:id='l2h-987' class="cmember">tp_dictoffset</tt></b></dt> | |
1129 | <dd> | |
1130 | If the instances of this type have a dictionary containing instance | |
1131 | variables, this field is non-zero and contains the offset in the | |
1132 | instances of the type of the instance variable dictionary; this | |
1133 | offset is used by <tt class="cfunction">PyObject_GenericGetAttr()</tt>. | |
1134 | ||
1135 | <P> | |
1136 | Do not confuse this field with <tt class="member">tp_dict</tt>; that is the | |
1137 | dictionary for attributes of the type object itself. | |
1138 | ||
1139 | <P> | |
1140 | If the value of this field is greater than zero, it specifies the | |
1141 | offset from the start of the instance structure. If the value is | |
1142 | less than zero, it specifies the offset from the <em>end</em> of the | |
1143 | instance structure. A negative offset is more expensive to use, and | |
1144 | should only be used when the instance structure contains a | |
1145 | variable-length part. This is used for example to add an instance | |
1146 | variable dictionary to subtypes of <tt class="class">str</tt> or <tt class="class">tuple</tt>. | |
1147 | Note that the <tt class="member">tp_basicsize</tt> field should account for the | |
1148 | dictionary added to the end in that case, even though the dictionary | |
1149 | is not included in the basic object layout. On a system with a | |
1150 | pointer size of 4 bytes, <tt class="member">tp_dictoffset</tt> should be set to | |
1151 | <code>-4</code> to indicate that the dictionary is at the very end of the | |
1152 | structure. | |
1153 | ||
1154 | <P> | |
1155 | The real dictionary offset in an instance can be computed from a | |
1156 | negative <tt class="member">tp_dictoffset</tt> as follows: | |
1157 | ||
1158 | <P> | |
1159 | <div class="verbatim"><pre> | |
1160 | dictoffset = tp_basicsize + abs(ob_size)*tp_itemsize + tp_dictoffset | |
1161 | if dictoffset is not aligned on sizeof(void*): | |
1162 | round up to sizeof(void*) | |
1163 | </pre></div> | |
1164 | ||
1165 | <P> | |
1166 | where <tt class="member">tp_basicsize</tt>, <tt class="member">tp_itemsize</tt> and | |
1167 | <tt class="member">tp_dictoffset</tt> are taken from the type object, and | |
1168 | <tt class="member">ob_size</tt> is taken from the instance. The absolute value is | |
1169 | taken because long ints use the sign of <tt class="member">ob_size</tt> to store | |
1170 | the sign of the number. (There's never a need to do this | |
1171 | calculation yourself; it is done for you by | |
1172 | <tt class="cfunction">_PyObject_GetDictPtr()</tt>.) | |
1173 | ||
1174 | <P> | |
1175 | This field is inherited by subtypes, but see the rules listed below. | |
1176 | A subtype may override this offset; this means that the subtype | |
1177 | instances store the dictionary at a difference offset than the base | |
1178 | type. Since the dictionary is always found via | |
1179 | <tt class="member">tp_dictoffset</tt>, this should not be a problem. | |
1180 | ||
1181 | <P> | |
1182 | When a type defined by a class statement has no <tt class="member">__slots__</tt> | |
1183 | declaration, and none of its base types has an instance variable | |
1184 | dictionary, a dictionary slot is added to the instance layout and | |
1185 | the <tt class="member">tp_dictoffset</tt> is set to that slot's offset. | |
1186 | ||
1187 | <P> | |
1188 | When a type defined by a class statement has a <tt class="member">__slots__</tt> | |
1189 | declaration, the type inherits its <tt class="member">tp_dictoffset</tt> from its | |
1190 | base type. | |
1191 | ||
1192 | <P> | |
1193 | (Adding a slot named <tt class="member">__dict__</tt> to the <tt class="member">__slots__</tt> | |
1194 | declaration does not have the expected effect, it just causes | |
1195 | confusion. Maybe this should be added as a feature just like | |
1196 | <tt class="member">__weakref__</tt> though.) | |
1197 | </dl> | |
1198 | ||
1199 | <P> | |
1200 | <dl><dt>initproc <b><tt id='l2h-988' xml:id='l2h-988' class="cmember">tp_init</tt></b></dt> | |
1201 | <dd> | |
1202 | An optional pointer to an instance initialization function. | |
1203 | ||
1204 | <P> | |
1205 | This function corresponds to the <tt class="method">__init__()</tt> method of | |
1206 | classes. Like <tt class="method">__init__()</tt>, it is possible to create an | |
1207 | instance without calling <tt class="method">__init__()</tt>, and it is possible to | |
1208 | reinitialize an instance by calling its <tt class="method">__init__()</tt> method | |
1209 | again. | |
1210 | ||
1211 | <P> | |
1212 | The function signature is | |
1213 | ||
1214 | <P> | |
1215 | <div class="verbatim"><pre> | |
1216 | int tp_init(PyObject *self, PyObject *args, PyObject *kwds) | |
1217 | </pre></div> | |
1218 | ||
1219 | <P> | |
1220 | The self argument is the instance to be initialized; the <var>args</var> | |
1221 | and <var>kwds</var> arguments represent positional and keyword arguments | |
1222 | of the call to <tt class="method">__init__()</tt>. | |
1223 | ||
1224 | <P> | |
1225 | The <tt class="member">tp_init</tt> function, if not <tt class="constant">NULL</tt>, is called when an | |
1226 | instance is created normally by calling its type, after the type's | |
1227 | <tt class="member">tp_new</tt> function has returned an instance of the type. If | |
1228 | the <tt class="member">tp_new</tt> function returns an instance of some other type | |
1229 | that is not a subtype of the original type, no <tt class="member">tp_init</tt> | |
1230 | function is called; if <tt class="member">tp_new</tt> returns an instance of a | |
1231 | subtype of the original type, the subtype's <tt class="member">tp_init</tt> is | |
1232 | called. (VERSION NOTE: described here is what is implemented in | |
1233 | Python 2.2.1 and later. In Python 2.2, the <tt class="member">tp_init</tt> of the | |
1234 | type of the object returned by <tt class="member">tp_new</tt> was always called, if | |
1235 | not <tt class="constant">NULL</tt>.) | |
1236 | ||
1237 | <P> | |
1238 | This field is inherited by subtypes. | |
1239 | </dl> | |
1240 | ||
1241 | <P> | |
1242 | <dl><dt>allocfunc <b><tt id='l2h-989' xml:id='l2h-989' class="cmember">tp_alloc</tt></b></dt> | |
1243 | <dd> | |
1244 | An optional pointer to an instance allocation function. | |
1245 | ||
1246 | <P> | |
1247 | The function signature is | |
1248 | ||
1249 | <P> | |
1250 | <div class="verbatim"><pre> | |
1251 | PyObject *tp_alloc(PyTypeObject *self, int nitems) | |
1252 | </pre></div> | |
1253 | ||
1254 | <P> | |
1255 | The purpose of this function is to separate memory allocation from | |
1256 | memory initialization. It should return a pointer to a block of | |
1257 | memory of adequate length for the instance, suitably aligned, and | |
1258 | initialized to zeros, but with <tt class="member">ob_refcnt</tt> set to <code>1</code> | |
1259 | and <tt class="member">ob_type</tt> set to the type argument. If the type's | |
1260 | <tt class="member">tp_itemsize</tt> is non-zero, the object's <tt class="member">ob_size</tt> field | |
1261 | should be initialized to <var>nitems</var> and the length of the | |
1262 | allocated memory block should be <code>tp_basicsize + | |
1263 | <var>nitems</var>*tp_itemsize</code>, rounded up to a multiple of | |
1264 | <code>sizeof(void*)</code>; otherwise, <var>nitems</var> is not used and the | |
1265 | length of the block should be <tt class="member">tp_basicsize</tt>. | |
1266 | ||
1267 | <P> | |
1268 | Do not use this function to do any other instance initialization, | |
1269 | not even to allocate additional memory; that should be done by | |
1270 | <tt class="member">tp_new</tt>. | |
1271 | ||
1272 | <P> | |
1273 | This field is inherited by static subtypes, but not by dynamic | |
1274 | subtypes (subtypes created by a class statement); in the latter, | |
1275 | this field is always set to <tt class="cfunction">PyType_GenericAlloc()</tt>, to | |
1276 | force a standard heap allocation strategy. That is also the | |
1277 | recommended value for statically defined types. | |
1278 | </dl> | |
1279 | ||
1280 | <P> | |
1281 | <dl><dt>newfunc <b><tt id='l2h-990' xml:id='l2h-990' class="cmember">tp_new</tt></b></dt> | |
1282 | <dd> | |
1283 | An optional pointer to an instance creation function. | |
1284 | ||
1285 | <P> | |
1286 | If this function is <tt class="constant">NULL</tt> for a particular type, that type cannot | |
1287 | be called to create new instances; presumably there is some other | |
1288 | way to create instances, like a factory function. | |
1289 | ||
1290 | <P> | |
1291 | The function signature is | |
1292 | ||
1293 | <P> | |
1294 | <div class="verbatim"><pre> | |
1295 | PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds) | |
1296 | </pre></div> | |
1297 | ||
1298 | <P> | |
1299 | The subtype argument is the type of the object being created; the | |
1300 | <var>args</var> and <var>kwds</var> arguments represent positional and keyword | |
1301 | arguments of the call to the type. Note that subtype doesn't have | |
1302 | to equal the type whose <tt class="member">tp_new</tt> function is called; it may | |
1303 | be a subtype of that type (but not an unrelated type). | |
1304 | ||
1305 | <P> | |
1306 | The <tt class="member">tp_new</tt> function should call | |
1307 | <code><var>subtype</var>->tp_alloc(<var>subtype</var>, <var>nitems</var>)</code> to | |
1308 | allocate space for the object, and then do only as much further | |
1309 | initialization as is absolutely necessary. Initialization that can | |
1310 | safely be ignored or repeated should be placed in the | |
1311 | <tt class="member">tp_init</tt> handler. A good rule of thumb is that for | |
1312 | immutable types, all initialization should take place in | |
1313 | <tt class="member">tp_new</tt>, while for mutable types, most initialization should | |
1314 | be deferred to <tt class="member">tp_init</tt>. | |
1315 | ||
1316 | <P> | |
1317 | This field is inherited by subtypes, except it is not inherited by | |
1318 | static types whose <tt class="member">tp_base</tt> is <tt class="constant">NULL</tt> or | |
1319 | <code>&PyBaseObject_Type</code>. The latter exception is a precaution so | |
1320 | that old extension types don't become callable simply by being | |
1321 | linked with Python 2.2. | |
1322 | </dl> | |
1323 | ||
1324 | <P> | |
1325 | <dl><dt>destructor <b><tt id='l2h-991' xml:id='l2h-991' class="cmember">tp_free</tt></b></dt> | |
1326 | <dd> | |
1327 | An optional pointer to an instance deallocation function. | |
1328 | ||
1329 | <P> | |
1330 | The signature of this function has changed slightly: in Python | |
1331 | 2.2 and 2.2.1, its signature is <tt class="ctype">destructor</tt>: | |
1332 | ||
1333 | <P> | |
1334 | <div class="verbatim"><pre> | |
1335 | void tp_free(PyObject *) | |
1336 | </pre></div> | |
1337 | ||
1338 | <P> | |
1339 | In Python 2.3 and beyond, its signature is <tt class="ctype">freefunc</tt>: | |
1340 | ||
1341 | <P> | |
1342 | <div class="verbatim"><pre> | |
1343 | void tp_free(void *) | |
1344 | </pre></div> | |
1345 | ||
1346 | <P> | |
1347 | The only initializer that is compatible with both versions is | |
1348 | <code>_PyObject_Del</code>, whose definition has suitably adapted in | |
1349 | Python 2.3. | |
1350 | ||
1351 | <P> | |
1352 | This field is inherited by static subtypes, but not by dynamic | |
1353 | subtypes (subtypes created by a class statement); in the latter, | |
1354 | this field is set to a deallocator suitable to match | |
1355 | <tt class="cfunction">PyType_GenericAlloc()</tt> and the value of the | |
1356 | <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit. | |
1357 | </dl> | |
1358 | ||
1359 | <P> | |
1360 | <dl><dt>inquiry <b><tt id='l2h-992' xml:id='l2h-992' class="cmember">tp_is_gc</tt></b></dt> | |
1361 | <dd> | |
1362 | An optional pointer to a function called by the garbage collector. | |
1363 | ||
1364 | <P> | |
1365 | The garbage collector needs to know whether a particular object is | |
1366 | collectible or not. Normally, it is sufficient to look at the | |
1367 | object's type's <tt class="member">tp_flags</tt> field, and check the | |
1368 | <tt class="constant">Py_TPFLAGS_HAVE_GC</tt> flag bit. But some types have a | |
1369 | mixture of statically and dynamically allocated instances, and the | |
1370 | statically allocated instances are not collectible. Such types | |
1371 | should define this function; it should return <code>1</code> for a | |
1372 | collectible instance, and <code>0</code> for a non-collectible instance. | |
1373 | The signature is | |
1374 | ||
1375 | <P> | |
1376 | <div class="verbatim"><pre> | |
1377 | int tp_is_gc(PyObject *self) | |
1378 | </pre></div> | |
1379 | ||
1380 | <P> | |
1381 | (The only example of this are types themselves. The metatype, | |
1382 | <tt class="cdata">PyType_Type</tt>, defines this function to distinguish between | |
1383 | statically and dynamically allocated types.) | |
1384 | ||
1385 | <P> | |
1386 | This field is inherited by subtypes. (VERSION NOTE: in Python | |
1387 | 2.2, it was not inherited. It is inherited in 2.2.1 and later | |
1388 | versions.) | |
1389 | </dl> | |
1390 | ||
1391 | <P> | |
1392 | <dl><dt>PyObject* <b><tt id='l2h-993' xml:id='l2h-993' class="cmember">tp_bases</tt></b></dt> | |
1393 | <dd> | |
1394 | Tuple of base types. | |
1395 | ||
1396 | <P> | |
1397 | This is set for types created by a class statement. It should be | |
1398 | <tt class="constant">NULL</tt> for statically defined types. | |
1399 | ||
1400 | <P> | |
1401 | This field is not inherited. | |
1402 | </dl> | |
1403 | ||
1404 | <P> | |
1405 | <dl><dt>PyObject* <b><tt id='l2h-994' xml:id='l2h-994' class="cmember">tp_mro</tt></b></dt> | |
1406 | <dd> | |
1407 | Tuple containing the expanded set of base types, starting with the | |
1408 | type itself and ending with <tt class="class">object</tt>, in Method Resolution | |
1409 | Order. | |
1410 | ||
1411 | <P> | |
1412 | This field is not inherited; it is calculated fresh by | |
1413 | <tt class="cfunction">PyType_Ready()</tt>. | |
1414 | </dl> | |
1415 | ||
1416 | <P> | |
1417 | <dl><dt>PyObject* <b><tt id='l2h-995' xml:id='l2h-995' class="cmember">tp_cache</tt></b></dt> | |
1418 | <dd> | |
1419 | Unused. Not inherited. Internal use only. | |
1420 | </dl> | |
1421 | ||
1422 | <P> | |
1423 | <dl><dt>PyObject* <b><tt id='l2h-996' xml:id='l2h-996' class="cmember">tp_subclasses</tt></b></dt> | |
1424 | <dd> | |
1425 | List of weak references to subclasses. Not inherited. Internal | |
1426 | use only. | |
1427 | </dl> | |
1428 | ||
1429 | <P> | |
1430 | <dl><dt>PyObject* <b><tt id='l2h-997' xml:id='l2h-997' class="cmember">tp_weaklist</tt></b></dt> | |
1431 | <dd> | |
1432 | Weak reference list head, for weak references to this type | |
1433 | object. Not inherited. Internal use only. | |
1434 | </dl> | |
1435 | ||
1436 | <P> | |
1437 | The remaining fields are only defined if the feature test macro | |
1438 | <tt class="constant">COUNT_ALLOCS</tt> is defined, and are for internal use only. | |
1439 | They are documented here for completeness. None of these fields are | |
1440 | inherited by subtypes. | |
1441 | ||
1442 | <P> | |
1443 | <dl><dt>int <b><tt id='l2h-998' xml:id='l2h-998' class="cmember">tp_allocs</tt></b></dt> | |
1444 | <dd> | |
1445 | Number of allocations. | |
1446 | </dl> | |
1447 | ||
1448 | <P> | |
1449 | <dl><dt>int <b><tt id='l2h-999' xml:id='l2h-999' class="cmember">tp_frees</tt></b></dt> | |
1450 | <dd> | |
1451 | Number of frees. | |
1452 | </dl> | |
1453 | ||
1454 | <P> | |
1455 | <dl><dt>int <b><tt id='l2h-1000' xml:id='l2h-1000' class="cmember">tp_maxalloc</tt></b></dt> | |
1456 | <dd> | |
1457 | Maximum simultaneously allocated objects. | |
1458 | </dl> | |
1459 | ||
1460 | <P> | |
1461 | <dl><dt>PyTypeObject* <b><tt id='l2h-1001' xml:id='l2h-1001' class="cmember">tp_next</tt></b></dt> | |
1462 | <dd> | |
1463 | Pointer to the next type object with a non-zero <tt class="member">tp_allocs</tt> | |
1464 | field. | |
1465 | </dl> | |
1466 | ||
1467 | <P> | |
1468 | Also, note that, in a garbage collected Python, tp_dealloc may be | |
1469 | called from any Python thread, not just the thread which created the | |
1470 | object (if the object becomes part of a refcount cycle, that cycle | |
1471 | might be collected by a garbage collection on any thread). This is | |
1472 | not a problem for Python API calls, since the thread on which | |
1473 | tp_dealloc is called will own the Global Interpreter Lock (GIL). | |
1474 | However, if the object being destroyed in turn destroys objects from | |
1475 | some other C or C++ library, care should be taken to ensure that | |
1476 | destroying those objects on the thread which called tp_dealloc will | |
1477 | not violate any assumptions of the library. | |
1478 | ||
1479 | <P> | |
1480 | ||
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