8 /* Object and type object interface */
11 Objects are structures allocated on the heap. Special rules apply to
12 the use of objects to ensure they are properly garbage-collected.
13 Objects are never allocated statically or on the stack; they must be
14 accessed through special macros and functions only. (Type objects are
15 exceptions to the first rule; the standard types are represented by
16 statically initialized type objects, although work on type/class unification
17 for Python 2.2 made it possible to have heap-allocated type objects too).
19 An object has a 'reference count' that is increased or decreased when a
20 pointer to the object is copied or deleted; when the reference count
21 reaches zero there are no references to the object left and it can be
22 removed from the heap.
24 An object has a 'type' that determines what it represents and what kind
25 of data it contains. An object's type is fixed when it is created.
26 Types themselves are represented as objects; an object contains a
27 pointer to the corresponding type object. The type itself has a type
28 pointer pointing to the object representing the type 'type', which
29 contains a pointer to itself!).
31 Objects do not float around in memory; once allocated an object keeps
32 the same size and address. Objects that must hold variable-size data
33 can contain pointers to variable-size parts of the object. Not all
34 objects of the same type have the same size; but the size cannot change
35 after allocation. (These restrictions are made so a reference to an
36 object can be simply a pointer -- moving an object would require
37 updating all the pointers, and changing an object's size would require
38 moving it if there was another object right next to it.)
40 Objects are always accessed through pointers of the type 'PyObject *'.
41 The type 'PyObject' is a structure that only contains the reference count
42 and the type pointer. The actual memory allocated for an object
43 contains other data that can only be accessed after casting the pointer
44 to a pointer to a longer structure type. This longer type must start
45 with the reference count and type fields; the macro PyObject_HEAD should be
46 used for this (to accommodate for future changes). The implementation
47 of a particular object type can cast the object pointer to the proper
50 A standard interface exists for objects that contain an array of items
51 whose size is determined when the object is allocated.
54 /* Py_DEBUG implies Py_TRACE_REFS. */
55 #if defined(Py_DEBUG) && !defined(Py_TRACE_REFS)
59 /* Py_TRACE_REFS implies Py_REF_DEBUG. */
60 #if defined(Py_TRACE_REFS) && !defined(Py_REF_DEBUG)
65 /* Define pointers to support a doubly-linked list of all live heap objects. */
66 #define _PyObject_HEAD_EXTRA \
67 struct _object *_ob_next; \
68 struct _object *_ob_prev;
70 #define _PyObject_EXTRA_INIT 0, 0,
73 #define _PyObject_HEAD_EXTRA
74 #define _PyObject_EXTRA_INIT
77 /* PyObject_HEAD defines the initial segment of every PyObject. */
78 #define PyObject_HEAD \
79 _PyObject_HEAD_EXTRA \
80 Py_ssize_t ob_refcnt; \
81 struct _typeobject *ob_type;
83 #define PyObject_HEAD_INIT(type) \
84 _PyObject_EXTRA_INIT \
87 #define PyVarObject_HEAD_INIT(type, size) \
88 PyObject_HEAD_INIT(type) size,
90 /* PyObject_VAR_HEAD defines the initial segment of all variable-size
91 * container objects. These end with a declaration of an array with 1
92 * element, but enough space is malloc'ed so that the array actually
93 * has room for ob_size elements. Note that ob_size is an element count,
94 * not necessarily a byte count.
96 #define PyObject_VAR_HEAD \
98 Py_ssize_t ob_size; /* Number of items in variable part */
99 #define Py_INVALID_SIZE (Py_ssize_t)-1
101 /* Nothing is actually declared to be a PyObject, but every pointer to
102 * a Python object can be cast to a PyObject*. This is inheritance built
103 * by hand. Similarly every pointer to a variable-size Python object can,
104 * in addition, be cast to PyVarObject*.
106 typedef struct _object
{
114 #define Py_REFCNT(ob) (((PyObject*)(ob))->ob_refcnt)
115 #define Py_TYPE(ob) (((PyObject*)(ob))->ob_type)
116 #define Py_SIZE(ob) (((PyVarObject*)(ob))->ob_size)
118 /* B/w compatibility */
119 #define Py_Refcnt(ob) Py_REFCNT(op)
120 #define Py_Type(op) Py_TYPE(op)
121 #define Py_Size(op) Py_SIZE(op)
124 Type objects contain a string containing the type name (to help somewhat
125 in debugging), the allocation parameters (see PyObject_New() and
127 and methods for accessing objects of the type. Methods are optional, a
128 nil pointer meaning that particular kind of access is not available for
129 this type. The Py_DECREF() macro uses the tp_dealloc method without
130 checking for a nil pointer; it should always be implemented except if
131 the implementation can guarantee that the reference count will never
132 reach zero (e.g., for statically allocated type objects).
134 NB: the methods for certain type groups are now contained in separate
138 typedef PyObject
* (*unaryfunc
)(PyObject
*);
139 typedef PyObject
* (*binaryfunc
)(PyObject
*, PyObject
*);
140 typedef PyObject
* (*ternaryfunc
)(PyObject
*, PyObject
*, PyObject
*);
141 typedef int (*inquiry
)(PyObject
*);
142 typedef Py_ssize_t (*lenfunc
)(PyObject
*);
143 typedef int (*coercion
)(PyObject
**, PyObject
**);
144 typedef PyObject
*(*intargfunc
)(PyObject
*, int) Py_DEPRECATED(2.5);
145 typedef PyObject
*(*intintargfunc
)(PyObject
*, int, int) Py_DEPRECATED(2.5);
146 typedef PyObject
*(*ssizeargfunc
)(PyObject
*, Py_ssize_t
);
147 typedef PyObject
*(*ssizessizeargfunc
)(PyObject
*, Py_ssize_t
, Py_ssize_t
);
148 typedef int(*intobjargproc
)(PyObject
*, int, PyObject
*);
149 typedef int(*intintobjargproc
)(PyObject
*, int, int, PyObject
*);
150 typedef int(*ssizeobjargproc
)(PyObject
*, Py_ssize_t
, PyObject
*);
151 typedef int(*ssizessizeobjargproc
)(PyObject
*, Py_ssize_t
, Py_ssize_t
, PyObject
*);
152 typedef int(*objobjargproc
)(PyObject
*, PyObject
*, PyObject
*);
154 /* int-based buffer interface */
155 typedef int (*getreadbufferproc
)(PyObject
*, int, void **);
156 typedef int (*getwritebufferproc
)(PyObject
*, int, void **);
157 typedef int (*getsegcountproc
)(PyObject
*, int *);
158 typedef int (*getcharbufferproc
)(PyObject
*, int, char **);
159 /* ssize_t-based buffer interface */
160 typedef Py_ssize_t (*readbufferproc
)(PyObject
*, Py_ssize_t
, void **);
161 typedef Py_ssize_t (*writebufferproc
)(PyObject
*, Py_ssize_t
, void **);
162 typedef Py_ssize_t (*segcountproc
)(PyObject
*, Py_ssize_t
*);
163 typedef Py_ssize_t (*charbufferproc
)(PyObject
*, Py_ssize_t
, char **);
165 typedef int (*objobjproc
)(PyObject
*, PyObject
*);
166 typedef int (*visitproc
)(PyObject
*, void *);
167 typedef int (*traverseproc
)(PyObject
*, visitproc
, void *);
170 /* For numbers without flag bit Py_TPFLAGS_CHECKTYPES set, all
171 arguments are guaranteed to be of the object's type (modulo
172 coercion hacks -- i.e. if the type's coercion function
173 returns other types, then these are allowed as well). Numbers that
174 have the Py_TPFLAGS_CHECKTYPES flag bit set should check *both*
175 arguments for proper type and implement the necessary conversions
176 in the slot functions themselves. */
179 binaryfunc nb_subtract
;
180 binaryfunc nb_multiply
;
181 binaryfunc nb_divide
;
182 binaryfunc nb_remainder
;
183 binaryfunc nb_divmod
;
184 ternaryfunc nb_power
;
185 unaryfunc nb_negative
;
186 unaryfunc nb_positive
;
187 unaryfunc nb_absolute
;
190 binaryfunc nb_lshift
;
191 binaryfunc nb_rshift
;
201 /* Added in release 2.0 */
202 binaryfunc nb_inplace_add
;
203 binaryfunc nb_inplace_subtract
;
204 binaryfunc nb_inplace_multiply
;
205 binaryfunc nb_inplace_divide
;
206 binaryfunc nb_inplace_remainder
;
207 ternaryfunc nb_inplace_power
;
208 binaryfunc nb_inplace_lshift
;
209 binaryfunc nb_inplace_rshift
;
210 binaryfunc nb_inplace_and
;
211 binaryfunc nb_inplace_xor
;
212 binaryfunc nb_inplace_or
;
214 /* Added in release 2.2 */
215 /* The following require the Py_TPFLAGS_HAVE_CLASS flag */
216 binaryfunc nb_floor_divide
;
217 binaryfunc nb_true_divide
;
218 binaryfunc nb_inplace_floor_divide
;
219 binaryfunc nb_inplace_true_divide
;
221 /* Added in release 2.5 */
227 binaryfunc sq_concat
;
228 ssizeargfunc sq_repeat
;
229 ssizeargfunc sq_item
;
230 ssizessizeargfunc sq_slice
;
231 ssizeobjargproc sq_ass_item
;
232 ssizessizeobjargproc sq_ass_slice
;
233 objobjproc sq_contains
;
234 /* Added in release 2.0 */
235 binaryfunc sq_inplace_concat
;
236 ssizeargfunc sq_inplace_repeat
;
241 binaryfunc mp_subscript
;
242 objobjargproc mp_ass_subscript
;
246 readbufferproc bf_getreadbuffer
;
247 writebufferproc bf_getwritebuffer
;
248 segcountproc bf_getsegcount
;
249 charbufferproc bf_getcharbuffer
;
253 typedef void (*freefunc
)(void *);
254 typedef void (*destructor
)(PyObject
*);
255 typedef int (*printfunc
)(PyObject
*, FILE *, int);
256 typedef PyObject
*(*getattrfunc
)(PyObject
*, char *);
257 typedef PyObject
*(*getattrofunc
)(PyObject
*, PyObject
*);
258 typedef int (*setattrfunc
)(PyObject
*, char *, PyObject
*);
259 typedef int (*setattrofunc
)(PyObject
*, PyObject
*, PyObject
*);
260 typedef int (*cmpfunc
)(PyObject
*, PyObject
*);
261 typedef PyObject
*(*reprfunc
)(PyObject
*);
262 typedef long (*hashfunc
)(PyObject
*);
263 typedef PyObject
*(*richcmpfunc
) (PyObject
*, PyObject
*, int);
264 typedef PyObject
*(*getiterfunc
) (PyObject
*);
265 typedef PyObject
*(*iternextfunc
) (PyObject
*);
266 typedef PyObject
*(*descrgetfunc
) (PyObject
*, PyObject
*, PyObject
*);
267 typedef int (*descrsetfunc
) (PyObject
*, PyObject
*, PyObject
*);
268 typedef int (*initproc
)(PyObject
*, PyObject
*, PyObject
*);
269 typedef PyObject
*(*newfunc
)(struct _typeobject
*, PyObject
*, PyObject
*);
270 typedef PyObject
*(*allocfunc
)(struct _typeobject
*, Py_ssize_t
);
272 typedef struct _typeobject
{
274 const char *tp_name
; /* For printing, in format "<module>.<name>" */
275 Py_ssize_t tp_basicsize
, tp_itemsize
; /* For allocation */
277 /* Methods to implement standard operations */
279 destructor tp_dealloc
;
281 getattrfunc tp_getattr
;
282 setattrfunc tp_setattr
;
286 /* Method suites for standard classes */
288 PyNumberMethods
*tp_as_number
;
289 PySequenceMethods
*tp_as_sequence
;
290 PyMappingMethods
*tp_as_mapping
;
292 /* More standard operations (here for binary compatibility) */
297 getattrofunc tp_getattro
;
298 setattrofunc tp_setattro
;
300 /* Functions to access object as input/output buffer */
301 PyBufferProcs
*tp_as_buffer
;
303 /* Flags to define presence of optional/expanded features */
306 const char *tp_doc
; /* Documentation string */
308 /* Assigned meaning in release 2.0 */
309 /* call function for all accessible objects */
310 traverseproc tp_traverse
;
312 /* delete references to contained objects */
315 /* Assigned meaning in release 2.1 */
316 /* rich comparisons */
317 richcmpfunc tp_richcompare
;
319 /* weak reference enabler */
320 Py_ssize_t tp_weaklistoffset
;
322 /* Added in release 2.2 */
325 iternextfunc tp_iternext
;
327 /* Attribute descriptor and subclassing stuff */
328 struct PyMethodDef
*tp_methods
;
329 struct PyMemberDef
*tp_members
;
330 struct PyGetSetDef
*tp_getset
;
331 struct _typeobject
*tp_base
;
333 descrgetfunc tp_descr_get
;
334 descrsetfunc tp_descr_set
;
335 Py_ssize_t tp_dictoffset
;
339 freefunc tp_free
; /* Low-level free-memory routine */
340 inquiry tp_is_gc
; /* For PyObject_IS_GC */
342 PyObject
*tp_mro
; /* method resolution order */
344 PyObject
*tp_subclasses
;
345 PyObject
*tp_weaklist
;
348 /* Type attribute cache version tag. Added in version 2.6 */
349 unsigned int tp_version_tag
;
352 /* these must be last and never explicitly initialized */
353 Py_ssize_t tp_allocs
;
355 Py_ssize_t tp_maxalloc
;
356 struct _typeobject
*tp_prev
;
357 struct _typeobject
*tp_next
;
362 /* The *real* layout of a type object when allocated on the heap */
363 typedef struct _heaptypeobject
{
364 /* Note: there's a dependency on the order of these members
365 in slotptr() in typeobject.c . */
366 PyTypeObject ht_type
;
367 PyNumberMethods as_number
;
368 PyMappingMethods as_mapping
;
369 PySequenceMethods as_sequence
; /* as_sequence comes after as_mapping,
370 so that the mapping wins when both
371 the mapping and the sequence define
372 a given operator (e.g. __getitem__).
373 see add_operators() in typeobject.c . */
374 PyBufferProcs as_buffer
;
375 PyObject
*ht_name
, *ht_slots
;
376 /* here are optional user slots, followed by the members. */
379 /* access macro to the members which are floating "behind" the object */
380 #define PyHeapType_GET_MEMBERS(etype) \
381 ((PyMemberDef *)(((char *)etype) + Py_TYPE(etype)->tp_basicsize))
384 /* Generic type check */
385 PyAPI_FUNC(int) PyType_IsSubtype(PyTypeObject
*, PyTypeObject
*);
386 #define PyObject_TypeCheck(ob, tp) \
387 (Py_TYPE(ob) == (tp) || PyType_IsSubtype(Py_TYPE(ob), (tp)))
389 PyAPI_DATA(PyTypeObject
) PyType_Type
; /* built-in 'type' */
390 PyAPI_DATA(PyTypeObject
) PyBaseObject_Type
; /* built-in 'object' */
391 PyAPI_DATA(PyTypeObject
) PySuper_Type
; /* built-in 'super' */
393 #define PyType_Check(op) \
394 PyType_FastSubclass(Py_TYPE(op), Py_TPFLAGS_TYPE_SUBCLASS)
395 #define PyType_CheckExact(op) (Py_TYPE(op) == &PyType_Type)
397 PyAPI_FUNC(int) PyType_Ready(PyTypeObject
*);
398 PyAPI_FUNC(PyObject
*) PyType_GenericAlloc(PyTypeObject
*, Py_ssize_t
);
399 PyAPI_FUNC(PyObject
*) PyType_GenericNew(PyTypeObject
*,
400 PyObject
*, PyObject
*);
401 PyAPI_FUNC(PyObject
*) _PyType_Lookup(PyTypeObject
*, PyObject
*);
402 PyAPI_FUNC(unsigned int) PyType_ClearCache(void);
404 /* Generic operations on objects */
405 PyAPI_FUNC(int) PyObject_Print(PyObject
*, FILE *, int);
406 PyAPI_FUNC(void) _PyObject_Dump(PyObject
*);
407 PyAPI_FUNC(PyObject
*) PyObject_Repr(PyObject
*);
408 PyAPI_FUNC(PyObject
*) _PyObject_Str(PyObject
*);
409 PyAPI_FUNC(PyObject
*) PyObject_Str(PyObject
*);
410 #ifdef Py_USING_UNICODE
411 PyAPI_FUNC(PyObject
*) PyObject_Unicode(PyObject
*);
413 PyAPI_FUNC(int) PyObject_Compare(PyObject
*, PyObject
*);
414 PyAPI_FUNC(PyObject
*) PyObject_RichCompare(PyObject
*, PyObject
*, int);
415 PyAPI_FUNC(int) PyObject_RichCompareBool(PyObject
*, PyObject
*, int);
416 PyAPI_FUNC(PyObject
*) PyObject_GetAttrString(PyObject
*, const char *);
417 PyAPI_FUNC(int) PyObject_SetAttrString(PyObject
*, const char *, PyObject
*);
418 PyAPI_FUNC(int) PyObject_HasAttrString(PyObject
*, const char *);
419 PyAPI_FUNC(PyObject
*) PyObject_GetAttr(PyObject
*, PyObject
*);
420 PyAPI_FUNC(int) PyObject_SetAttr(PyObject
*, PyObject
*, PyObject
*);
421 PyAPI_FUNC(int) PyObject_HasAttr(PyObject
*, PyObject
*);
422 PyAPI_FUNC(PyObject
**) _PyObject_GetDictPtr(PyObject
*);
423 PyAPI_FUNC(PyObject
*) PyObject_SelfIter(PyObject
*);
424 PyAPI_FUNC(PyObject
*) PyObject_GenericGetAttr(PyObject
*, PyObject
*);
425 PyAPI_FUNC(int) PyObject_GenericSetAttr(PyObject
*,
426 PyObject
*, PyObject
*);
427 PyAPI_FUNC(long) PyObject_Hash(PyObject
*);
428 PyAPI_FUNC(int) PyObject_IsTrue(PyObject
*);
429 PyAPI_FUNC(int) PyObject_Not(PyObject
*);
430 PyAPI_FUNC(int) PyCallable_Check(PyObject
*);
431 PyAPI_FUNC(int) PyNumber_Coerce(PyObject
**, PyObject
**);
432 PyAPI_FUNC(int) PyNumber_CoerceEx(PyObject
**, PyObject
**);
434 PyAPI_FUNC(void) PyObject_ClearWeakRefs(PyObject
*);
436 /* A slot function whose address we need to compare */
437 extern int _PyObject_SlotCompare(PyObject
*, PyObject
*);
440 /* PyObject_Dir(obj) acts like Python __builtin__.dir(obj), returning a
441 list of strings. PyObject_Dir(NULL) is like __builtin__.dir(),
442 returning the names of the current locals. In this case, if there are
443 no current locals, NULL is returned, and PyErr_Occurred() is false.
445 PyAPI_FUNC(PyObject
*) PyObject_Dir(PyObject
*);
448 /* Helpers for printing recursive container types */
449 PyAPI_FUNC(int) Py_ReprEnter(PyObject
*);
450 PyAPI_FUNC(void) Py_ReprLeave(PyObject
*);
452 /* Helpers for hash functions */
453 PyAPI_FUNC(long) _Py_HashDouble(double);
454 PyAPI_FUNC(long) _Py_HashPointer(void*);
456 /* Helper for passing objects to printf and the like */
457 #define PyObject_REPR(obj) PyString_AS_STRING(PyObject_Repr(obj))
459 /* Flag bits for printing: */
460 #define Py_PRINT_RAW 1 /* No string quotes etc. */
463 `Type flags (tp_flags)
465 These flags are used to extend the type structure in a backwards-compatible
466 fashion. Extensions can use the flags to indicate (and test) when a given
467 type structure contains a new feature. The Python core will use these when
468 introducing new functionality between major revisions (to avoid mid-version
469 changes in the PYTHON_API_VERSION).
471 Arbitration of the flag bit positions will need to be coordinated among
472 all extension writers who publically release their extensions (this will
473 be fewer than you might expect!)..
475 Python 1.5.2 introduced the bf_getcharbuffer slot into PyBufferProcs.
477 Type definitions should use Py_TPFLAGS_DEFAULT for their tp_flags value.
479 Code can use PyType_HasFeature(type_ob, flag_value) to test whether the
480 given type object has a specified feature.
483 /* PyBufferProcs contains bf_getcharbuffer */
484 #define Py_TPFLAGS_HAVE_GETCHARBUFFER (1L<<0)
486 /* PySequenceMethods contains sq_contains */
487 #define Py_TPFLAGS_HAVE_SEQUENCE_IN (1L<<1)
489 /* This is here for backwards compatibility. Extensions that use the old GC
490 * API will still compile but the objects will not be tracked by the GC. */
491 #define Py_TPFLAGS_GC 0 /* used to be (1L<<2) */
493 /* PySequenceMethods and PyNumberMethods contain in-place operators */
494 #define Py_TPFLAGS_HAVE_INPLACEOPS (1L<<3)
496 /* PyNumberMethods do their own coercion */
497 #define Py_TPFLAGS_CHECKTYPES (1L<<4)
499 /* tp_richcompare is defined */
500 #define Py_TPFLAGS_HAVE_RICHCOMPARE (1L<<5)
502 /* Objects which are weakly referencable if their tp_weaklistoffset is >0 */
503 #define Py_TPFLAGS_HAVE_WEAKREFS (1L<<6)
505 /* tp_iter is defined */
506 #define Py_TPFLAGS_HAVE_ITER (1L<<7)
508 /* New members introduced by Python 2.2 exist */
509 #define Py_TPFLAGS_HAVE_CLASS (1L<<8)
511 /* Set if the type object is dynamically allocated */
512 #define Py_TPFLAGS_HEAPTYPE (1L<<9)
514 /* Set if the type allows subclassing */
515 #define Py_TPFLAGS_BASETYPE (1L<<10)
517 /* Set if the type is 'ready' -- fully initialized */
518 #define Py_TPFLAGS_READY (1L<<12)
520 /* Set while the type is being 'readied', to prevent recursive ready calls */
521 #define Py_TPFLAGS_READYING (1L<<13)
523 /* Objects support garbage collection (see objimp.h) */
524 #define Py_TPFLAGS_HAVE_GC (1L<<14)
526 /* These two bits are preserved for Stackless Python, next after this is 17 */
528 #define Py_TPFLAGS_HAVE_STACKLESS_EXTENSION (3L<<15)
530 #define Py_TPFLAGS_HAVE_STACKLESS_EXTENSION 0
533 /* Objects support nb_index in PyNumberMethods */
534 #define Py_TPFLAGS_HAVE_INDEX (1L<<17)
536 /* Objects support type attribute cache */
537 #define Py_TPFLAGS_HAVE_VERSION_TAG (1L<<18)
538 #define Py_TPFLAGS_VALID_VERSION_TAG (1L<<19)
540 /* Type is abstract and cannot be instantiated */
541 #define Py_TPFLAGS_IS_ABSTRACT (1L<<20)
543 /* These flags are used to determine if a type is a subclass. */
544 #define Py_TPFLAGS_INT_SUBCLASS (1L<<23)
545 #define Py_TPFLAGS_LONG_SUBCLASS (1L<<24)
546 #define Py_TPFLAGS_LIST_SUBCLASS (1L<<25)
547 #define Py_TPFLAGS_TUPLE_SUBCLASS (1L<<26)
548 #define Py_TPFLAGS_STRING_SUBCLASS (1L<<27)
549 #define Py_TPFLAGS_UNICODE_SUBCLASS (1L<<28)
550 #define Py_TPFLAGS_DICT_SUBCLASS (1L<<29)
551 #define Py_TPFLAGS_BASE_EXC_SUBCLASS (1L<<30)
552 #define Py_TPFLAGS_TYPE_SUBCLASS (1L<<31)
554 #define Py_TPFLAGS_DEFAULT ( \
555 Py_TPFLAGS_HAVE_GETCHARBUFFER | \
556 Py_TPFLAGS_HAVE_SEQUENCE_IN | \
557 Py_TPFLAGS_HAVE_INPLACEOPS | \
558 Py_TPFLAGS_HAVE_RICHCOMPARE | \
559 Py_TPFLAGS_HAVE_WEAKREFS | \
560 Py_TPFLAGS_HAVE_ITER | \
561 Py_TPFLAGS_HAVE_CLASS | \
562 Py_TPFLAGS_HAVE_STACKLESS_EXTENSION | \
563 Py_TPFLAGS_HAVE_INDEX | \
564 Py_TPFLAGS_HAVE_VERSION_TAG | \
567 #define PyType_HasFeature(t,f) (((t)->tp_flags & (f)) != 0)
568 #define PyType_FastSubclass(t,f) PyType_HasFeature(t,f)
572 The macros Py_INCREF(op) and Py_DECREF(op) are used to increment or decrement
573 reference counts. Py_DECREF calls the object's deallocator function when
574 the refcount falls to 0; for
575 objects that don't contain references to other objects or heap memory
576 this can be the standard function free(). Both macros can be used
577 wherever a void expression is allowed. The argument must not be a
578 NIL pointer. If it may be NIL, use Py_XINCREF/Py_XDECREF instead.
579 The macro _Py_NewReference(op) initialize reference counts to 1, and
580 in special builds (Py_REF_DEBUG, Py_TRACE_REFS) performs additional
581 bookkeeping appropriate to the special build.
583 We assume that the reference count field can never overflow; this can
584 be proven when the size of the field is the same as the pointer size, so
585 we ignore the possibility. Provided a C int is at least 32 bits (which
586 is implicitly assumed in many parts of this code), that's enough for
587 about 2**31 references to an object.
589 XXX The following became out of date in Python 2.2, but I'm not sure
590 XXX what the full truth is now. Certainly, heap-allocated type objects
591 XXX can and should be deallocated.
592 Type objects should never be deallocated; the type pointer in an object
593 is not considered to be a reference to the type object, to save
594 complications in the deallocation function. (This is actually a
595 decision that's up to the implementer of each new type so if you want,
596 you can count such references to the type object.)
598 *** WARNING*** The Py_DECREF macro must have a side-effect-free argument
599 since it may evaluate its argument multiple times. (The alternative
600 would be to mace it a proper function or assign it to a global temporary
601 variable first, both of which are slower; and in a multi-threaded
602 environment the global variable trick is not safe.)
605 /* First define a pile of simple helper macros, one set per special
606 * build symbol. These either expand to the obvious things, or to
607 * nothing at all when the special mode isn't in effect. The main
608 * macros can later be defined just once then, yet expand to different
609 * things depending on which special build options are and aren't in effect.
610 * Trust me <wink>: while painful, this is 20x easier to understand than,
611 * e.g, defining _Py_NewReference five different times in a maze of nested
612 * #ifdefs (we used to do that -- it was impenetrable).
615 PyAPI_DATA(Py_ssize_t
) _Py_RefTotal
;
616 PyAPI_FUNC(void) _Py_NegativeRefcount(const char *fname
,
617 int lineno
, PyObject
*op
);
618 PyAPI_FUNC(PyObject
*) _PyDict_Dummy(void);
619 PyAPI_FUNC(PyObject
*) _PySet_Dummy(void);
620 PyAPI_FUNC(Py_ssize_t
) _Py_GetRefTotal(void);
621 #define _Py_INC_REFTOTAL _Py_RefTotal++
622 #define _Py_DEC_REFTOTAL _Py_RefTotal--
623 #define _Py_REF_DEBUG_COMMA ,
624 #define _Py_CHECK_REFCNT(OP) \
625 { if (((PyObject*)OP)->ob_refcnt < 0) \
626 _Py_NegativeRefcount(__FILE__, __LINE__, \
630 #define _Py_INC_REFTOTAL
631 #define _Py_DEC_REFTOTAL
632 #define _Py_REF_DEBUG_COMMA
633 #define _Py_CHECK_REFCNT(OP) /* a semicolon */;
634 #endif /* Py_REF_DEBUG */
637 PyAPI_FUNC(void) inc_count(PyTypeObject
*);
638 PyAPI_FUNC(void) dec_count(PyTypeObject
*);
639 #define _Py_INC_TPALLOCS(OP) inc_count(Py_TYPE(OP))
640 #define _Py_INC_TPFREES(OP) dec_count(Py_TYPE(OP))
641 #define _Py_DEC_TPFREES(OP) Py_TYPE(OP)->tp_frees--
642 #define _Py_COUNT_ALLOCS_COMMA ,
644 #define _Py_INC_TPALLOCS(OP)
645 #define _Py_INC_TPFREES(OP)
646 #define _Py_DEC_TPFREES(OP)
647 #define _Py_COUNT_ALLOCS_COMMA
648 #endif /* COUNT_ALLOCS */
651 /* Py_TRACE_REFS is such major surgery that we call external routines. */
652 PyAPI_FUNC(void) _Py_NewReference(PyObject
*);
653 PyAPI_FUNC(void) _Py_ForgetReference(PyObject
*);
654 PyAPI_FUNC(void) _Py_Dealloc(PyObject
*);
655 PyAPI_FUNC(void) _Py_PrintReferences(FILE *);
656 PyAPI_FUNC(void) _Py_PrintReferenceAddresses(FILE *);
657 PyAPI_FUNC(void) _Py_AddToAllObjects(PyObject
*, int force
);
660 /* Without Py_TRACE_REFS, there's little enough to do that we expand code
663 #define _Py_NewReference(op) ( \
664 _Py_INC_TPALLOCS(op) _Py_COUNT_ALLOCS_COMMA \
665 _Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
668 #define _Py_ForgetReference(op) _Py_INC_TPFREES(op)
670 #define _Py_Dealloc(op) ( \
671 _Py_INC_TPFREES(op) _Py_COUNT_ALLOCS_COMMA \
672 (*Py_TYPE(op)->tp_dealloc)((PyObject *)(op)))
673 #endif /* !Py_TRACE_REFS */
675 #define Py_INCREF(op) ( \
676 _Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
677 ((PyObject*)(op))->ob_refcnt++)
679 #define Py_DECREF(op) \
680 if (_Py_DEC_REFTOTAL _Py_REF_DEBUG_COMMA \
681 --((PyObject*)(op))->ob_refcnt != 0) \
682 _Py_CHECK_REFCNT(op) \
684 _Py_Dealloc((PyObject *)(op))
686 /* Safely decref `op` and set `op` to NULL, especially useful in tp_clear
687 * and tp_dealloc implementatons.
689 * Note that "the obvious" code can be deadly:
694 * Typically, `op` is something like self->containee, and `self` is done
695 * using its `containee` member. In the code sequence above, suppose
696 * `containee` is non-NULL with a refcount of 1. Its refcount falls to
697 * 0 on the first line, which can trigger an arbitrary amount of code,
698 * possibly including finalizers (like __del__ methods or weakref callbacks)
699 * coded in Python, which in turn can release the GIL and allow other threads
700 * to run, etc. Such code may even invoke methods of `self` again, or cause
701 * cyclic gc to trigger, but-- oops! --self->containee still points to the
702 * object being torn down, and it may be in an insane state while being torn
703 * down. This has in fact been a rich historic source of miserable (rare &
704 * hard-to-diagnose) segfaulting (and other) bugs.
710 * That arranges to set `op` to NULL _before_ decref'ing, so that any code
711 * triggered as a side-effect of `op` getting torn down no longer believes
712 * `op` points to a valid object.
714 * There are cases where it's safe to use the naive code, but they're brittle.
715 * For example, if `op` points to a Python integer, you know that destroying
716 * one of those can't cause problems -- but in part that relies on that
717 * Python integers aren't currently weakly referencable. Best practice is
718 * to use Py_CLEAR() even if you can't think of a reason for why you need to.
720 #define Py_CLEAR(op) \
723 PyObject *tmp = (PyObject *)(op); \
729 /* Macros to use in case the object pointer may be NULL: */
730 #define Py_XINCREF(op) if ((op) == NULL) ; else Py_INCREF(op)
731 #define Py_XDECREF(op) if ((op) == NULL) ; else Py_DECREF(op)
734 These are provided as conveniences to Python runtime embedders, so that
735 they can have object code that is not dependent on Python compilation flags.
737 PyAPI_FUNC(void) Py_IncRef(PyObject
*);
738 PyAPI_FUNC(void) Py_DecRef(PyObject
*);
741 _Py_NoneStruct is an object of undefined type which can be used in contexts
742 where NULL (nil) is not suitable (since NULL often means 'error').
744 Don't forget to apply Py_INCREF() when returning this value!!!
746 PyAPI_DATA(PyObject
) _Py_NoneStruct
; /* Don't use this directly */
747 #define Py_None (&_Py_NoneStruct)
749 /* Macro for returning Py_None from a function */
750 #define Py_RETURN_NONE return Py_INCREF(Py_None), Py_None
753 Py_NotImplemented is a singleton used to signal that an operation is
754 not implemented for a given type combination.
756 PyAPI_DATA(PyObject
) _Py_NotImplementedStruct
; /* Don't use this directly */
757 #define Py_NotImplemented (&_Py_NotImplementedStruct)
759 /* Rich comparison opcodes */
767 /* Maps Py_LT to Py_GT, ..., Py_GE to Py_LE.
768 * Defined in object.c.
770 PyAPI_DATA(int) _Py_SwappedOp
[];
773 Define staticforward and statichere for source compatibility with old
776 The staticforward define was needed to support certain broken C
777 compilers (notably SCO ODT 3.0, perhaps early AIX as well) botched the
778 static keyword when it was used with a forward declaration of a static
779 initialized structure. Standard C allows the forward declaration with
780 static, and we've decided to stop catering to broken C compilers.
781 (In fact, we expect that the compilers are all fixed eight years later.)
784 #define staticforward static
785 #define statichere static
795 Functions that take objects as arguments normally don't check for nil
796 arguments, but they do check the type of the argument, and return an
797 error if the function doesn't apply to the type.
802 Functions may fail for a variety of reasons, including running out of
803 memory. This is communicated to the caller in two ways: an error string
804 is set (see errors.h), and the function result differs: functions that
805 normally return a pointer return NULL for failure, functions returning
806 an integer return -1 (which could be a legal return value too!), and
807 other functions return 0 for success and -1 for failure.
808 Callers should always check for errors before using the result. If
809 an error was set, the caller must either explicitly clear it, or pass
810 the error on to its caller.
815 It takes a while to get used to the proper usage of reference counts.
817 Functions that create an object set the reference count to 1; such new
818 objects must be stored somewhere or destroyed again with Py_DECREF().
819 Some functions that 'store' objects, such as PyTuple_SetItem() and
821 don't increment the reference count of the object, since the most
822 frequent use is to store a fresh object. Functions that 'retrieve'
823 objects, such as PyTuple_GetItem() and PyDict_GetItemString(), also
825 the reference count, since most frequently the object is only looked at
826 quickly. Thus, to retrieve an object and store it again, the caller
827 must call Py_INCREF() explicitly.
829 NOTE: functions that 'consume' a reference count, like
830 PyList_SetItem(), consume the reference even if the object wasn't
831 successfully stored, to simplify error handling.
833 It seems attractive to make other functions that take an object as
834 argument consume a reference count; however, this may quickly get
835 confusing (even the current practice is already confusing). Consider
836 it carefully, it may save lots of calls to Py_INCREF() and Py_DECREF() at
841 /* Trashcan mechanism, thanks to Christian Tismer.
843 When deallocating a container object, it's possible to trigger an unbounded
844 chain of deallocations, as each Py_DECREF in turn drops the refcount on "the
845 next" object in the chain to 0. This can easily lead to stack faults, and
846 especially in threads (which typically have less stack space to work with).
848 A container object that participates in cyclic gc can avoid this by
849 bracketing the body of its tp_dealloc function with a pair of macros:
852 mytype_dealloc(mytype *p)
854 ... declarations go here ...
856 PyObject_GC_UnTrack(p); // must untrack first
857 Py_TRASHCAN_SAFE_BEGIN(p)
858 ... The body of the deallocator goes here, including all calls ...
859 ... to Py_DECREF on contained objects. ...
860 Py_TRASHCAN_SAFE_END(p)
863 CAUTION: Never return from the middle of the body! If the body needs to
864 "get out early", put a label immediately before the Py_TRASHCAN_SAFE_END
865 call, and goto it. Else the call-depth counter (see below) will stay
866 above 0 forever, and the trashcan will never get emptied.
868 How it works: The BEGIN macro increments a call-depth counter. So long
869 as this counter is small, the body of the deallocator is run directly without
870 further ado. But if the counter gets large, it instead adds p to a list of
871 objects to be deallocated later, skips the body of the deallocator, and
872 resumes execution after the END macro. The tp_dealloc routine then returns
873 without deallocating anything (and so unbounded call-stack depth is avoided).
875 When the call stack finishes unwinding again, code generated by the END macro
876 notices this, and calls another routine to deallocate all the objects that
877 may have been added to the list of deferred deallocations. In effect, a
878 chain of N deallocations is broken into N / PyTrash_UNWIND_LEVEL pieces,
879 with the call stack never exceeding a depth of PyTrash_UNWIND_LEVEL.
882 PyAPI_FUNC(void) _PyTrash_deposit_object(PyObject
*);
883 PyAPI_FUNC(void) _PyTrash_destroy_chain(void);
884 PyAPI_DATA(int) _PyTrash_delete_nesting
;
885 PyAPI_DATA(PyObject
*) _PyTrash_delete_later
;
887 #define PyTrash_UNWIND_LEVEL 50
889 #define Py_TRASHCAN_SAFE_BEGIN(op) \
890 if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL) { \
891 ++_PyTrash_delete_nesting;
892 /* The body of the deallocator is here. */
893 #define Py_TRASHCAN_SAFE_END(op) \
894 --_PyTrash_delete_nesting; \
895 if (_PyTrash_delete_later && _PyTrash_delete_nesting <= 0) \
896 _PyTrash_destroy_chain(); \
899 _PyTrash_deposit_object((PyObject*)op);
904 #endif /* !Py_OBJECT_H */