Type Object Structures

Type Object Structures¶
Perhaps one of the most important structures of the Python object system is the
structure that defines a new type: the PyTypeObject
structure. Type
objects can be handled using any of the PyObject_*
or
PyType_*
functions, but do not offer much that’s interesting to most
Python applications. These objects are fundamental to how objects behave, so
they are very important to the interpreter itself and to any extension module
that implements new types.
Type objects are fairly large compared to most of the standard types. The reason for the size is that each type object stores a large number of values, mostly C function pointers, each of which implements a small part of the type’s functionality. The fields of the type object are examined in detail in this section. The fields will be described in the order in which they occur in the structure.
In addition to the following quick reference, the Examples
section provides at-a-glance insight into the meaning and use of
PyTypeObject
.
Quick Reference¶
“tp slots”¶
PyTypeObject Slot [1] |
special methods/attrs |
Info [2] |
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|---|---|---|---|---|---|---|
O |
T |
D |
I |
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<R> |
const char * |
__name__ |
X |
X |
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X |
X |
X |
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X |
X |
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X |
X |
X |
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X |
X |
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__getattribute__, __getattr__ |
G |
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__setattr__, __delattr__ |
G |
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% |
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__repr__ |
X |
X |
X |
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% |
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% |
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% |
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__hash__ |
X |
G |
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__call__ |
X |
X |
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__str__ |
X |
X |
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__getattribute__, __getattr__ |
X |
X |
G |
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__setattr__, __delattr__ |
X |
X |
G |
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% |
||||||
unsigned long |
X |
X |
? |
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const char * |
__doc__ |
X |
X |
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X |
G |
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X |
G |
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__lt__, __le__, __eq__, __ne__, __gt__, __ge__ |
X |
G |
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X |
? |
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__iter__ |
X |
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__next__ |
X |
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|
X |
X |
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X |
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X |
X |
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__base__ |
X |
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|
__dict__ |
? |
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__get__ |
X |
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__set__, __delete__ |
X |
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X |
? |
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__init__ |
X |
X |
X |
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X |
? |
? |
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__new__ |
X |
X |
? |
? |
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X |
X |
? |
? |
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X |
X |
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< |
|
__bases__ |
~ |
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< |
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__mro__ |
~ |
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[ |
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void * |
__subclasses__ |
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( |
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unsigned int |
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__del__ |
X |
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unsigned char |
sub-slots¶
Slot |
special methods |
|
|---|---|---|
__await__ |
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__aiter__ |
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__anext__ |
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__add__ __radd__ |
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__iadd__ |
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__sub__ __rsub__ |
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__isub__ |
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__mul__ __rmul__ |
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__imul__ |
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__mod__ __rmod__ |
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__imod__ |
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__divmod__ __rdivmod__ |
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__pow__ __rpow__ |
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__ipow__ |
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__neg__ |
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__pos__ |
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__abs__ |
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__bool__ |
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__invert__ |
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__lshift__ __rlshift__ |
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__ilshift__ |
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__rshift__ __rrshift__ |
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__irshift__ |
||
__and__ __rand__ |
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__iand__ |
||
__xor__ __rxor__ |
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__ixor__ |
||
__or__ __ror__ |
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__ior__ |
||
__int__ |
||
void * |
||
__float__ |
||
__floordiv__ |
||
__ifloordiv__ |
||
__truediv__ |
||
__itruediv__ |
||
__index__ |
||
__matmul__ __rmatmul__ |
||
__imatmul__ |
||
__len__ |
||
__getitem__ |
||
__setitem__, __delitem__ |
||
__len__ |
||
__add__ |
||
__mul__ |
||
__getitem__ |
||
__setitem__ __delitem__ |
||
__contains__ |
||
__iadd__ |
||
__imul__ |
||
__buffer__ |
||
__release_buffer__ |
slot typedefs¶
typedef |
Parameter Types |
Return Type |
|---|---|---|
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void |
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void * |
void |
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int |
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int |
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PyObject *const char *
|
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int |
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int |
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int |
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|
Py_hash_t |
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int |
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void |
||
|
int |
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PyObject * |
|
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int |
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int |
||
int |
See Slot Type typedefs below for more detail.
PyTypeObject Definition¶
The structure definition for PyTypeObject
can be found in
Include/cpython/object.h
. For convenience of reference, this repeats the
definition found there:
typedef struct _typeobject {
PyObject_VAR_HEAD
const char *tp_name; /* For printing, in format "<module>.<name>" */
Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */
/* Methods to implement standard operations */
destructor tp_dealloc;
Py_ssize_t tp_vectorcall_offset;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
or tp_reserved (Python 3) */
reprfunc tp_repr;
/* Method suites for standard classes */
PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;
/* More standard operations (here for binary compatibility) */
hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;
/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;
/* Flags to define presence of optional/expanded features */
unsigned long tp_flags;
const char *tp_doc; /* Documentation string */
/* Assigned meaning in release 2.0 */
/* call function for all accessible objects */
traverseproc tp_traverse;
/* delete references to contained objects */
inquiry tp_clear;
/* Assigned meaning in release 2.1 */
/* rich comparisons */
richcmpfunc tp_richcompare;
/* weak reference enabler */
Py_ssize_t tp_weaklistoffset;
/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;
/* Attribute descriptor and subclassing stuff */
PyMethodDef *tp_methods;
PyMemberDef *tp_members;
PyGetSetDef *tp_getset;
// Strong reference on a heap type, borrowed reference on a static type
PyTypeObject *tp_base;
PyObject *tp_dict;
descrgetfunc tp_descr_get;
descrsetfunc tp_descr_set;
Py_ssize_t tp_dictoffset;
initproc tp_init;
allocfunc tp_alloc;
newfunc tp_new;
freefunc tp_free; /* Low-level free-memory routine */
inquiry tp_is_gc; /* For PyObject_IS_GC */
PyObject *tp_bases;
PyObject *tp_mro; /* method resolution order */
PyObject *tp_cache; /* no longer used */
void *tp_subclasses; /* for static builtin types this is an index */
PyObject *tp_weaklist; /* not used for static builtin types */
destructor tp_del;
/* Type attribute cache version tag. Added in version 2.6.
* If zero, the cache is invalid and must be initialized.
*/
unsigned int tp_version_tag;
destructor tp_finalize;
vectorcallfunc tp_vectorcall;
/* bitset of which type-watchers care about this type */
unsigned char tp_watched;
/* Number of tp_version_tag values used.
* Set to _Py_ATTR_CACHE_UNUSED if the attribute cache is
* disabled for this type (e.g. due to custom MRO entries).
* Otherwise, limited to MAX_VERSIONS_PER_CLASS (defined elsewhere).
*/
uint16_t tp_versions_used;
} PyTypeObject;
PyObject Slots¶
The type object structure extends the PyVarObject
structure. The
ob_size
field is used for dynamic types (created by type_new()
,
usually called from a class statement). Note that PyType_Type
(the
metatype) initializes tp_itemsize
, which means that its instances (i.e.
type objects) must have the ob_size
field.
The type object’s reference count is initialized to
1
by thePyObject_HEAD_INIT
macro. Note that for statically allocated type objects, the type’s instances (objects whoseob_type
points back to the type) do not count as references. But for dynamically allocated type objects, the instances do count as references.Inheritance:
This field is not inherited by subtypes.
This is the type’s type, in other words its metatype. It is initialized by the argument to the
PyObject_HEAD_INIT
macro, and its value should normally be&PyType_Type
. However, for dynamically loadable extension modules that must be usable on Windows (at least), the compiler complains that this is not a valid initializer. Therefore, the convention is to passNULL
to thePyObject_HEAD_INIT
macro and to initialize this field explicitly at the start of the module’s initialization function, before doing anything else. This is typically done like this:Foo_Type.ob_type = &PyType_Type;This should be done before any instances of the type are created.
PyType_Ready()
checks ifob_type
isNULL
, and if so, initializes it to theob_type
field of the base class.PyType_Ready()
will not change this field if it is non-zero.Inheritance:
This field is inherited by subtypes.
PyVarObject Slots¶
For statically allocated type objects, this should be initialized to zero. For dynamically allocated type objects, this field has a special internal meaning.
This field should be accessed using the
Py_SIZE()
macro.Inheritance:
This field is not inherited by subtypes.
PyTypeObject Slots¶
Each slot has a section describing inheritance. If PyType_Ready()
may set a value when the field is set to NULL
then there will also be
a “Default” section. (Note that many fields set on PyBaseObject_Type
and PyType_Type
effectively act as defaults.)
-
const char *PyTypeObject.tp_name¶
Pointer to a NUL-terminated string containing the name of the type. For types that are accessible as module globals, the string should be the full module name, followed by a dot, followed by the type name; for built-in types, it should be just the type name. If the module is a submodule of a package, the full package name is part of the full module name. For example, a type named
T
defined in moduleM
in subpackageQ
in packageP
should have thetp_name
initializer"P.Q.M.T"
.For dynamically allocated type objects, this should just be the type name, and the module name explicitly stored in the type dict as the value for key
'__module__'
.For statically allocated type objects, the tp_name field should contain a dot. Everything before the last dot is made accessible as the
__module__
attribute, and everything after the last dot is made accessible as the__name__
attribute.If no dot is present, the entire
tp_name
field is made accessible as the__name__
attribute, and the__module__
attribute is undefined (unless explicitly set in the dictionary, as explained above). This means your type will be impossible to pickle. Additionally, it will not be listed in module documentations created with pydoc.This field must not be
NULL
. It is the only required field inPyTypeObject()
(other than potentiallytp_itemsize
).Inheritance:
This field is not inherited by subtypes.
-
Py_ssize_t PyTypeObject.tp_basicsize¶
-
Py_ssize_t PyTypeObject.tp_itemsize¶
These fields allow calculating the size in bytes of instances of the type.
There are two kinds of types: types with fixed-length instances have a zero
tp_itemsize
field, types with variable-length instances have a non-zerotp_itemsize
field. For a type with fixed-length instances, all instances have the same size, given intp_basicsize
. (Exceptions to this rule can be made usingPyUnstable_Object_GC_NewWithExtraData()
.)For a type with variable-length instances, the instances must have an
ob_size
field, and the instance size istp_basicsize
plus N timestp_itemsize
, where N is the “length” of the object.Functions like
PyObject_NewVar()
will take the value of N as an argument, and store in the instance’sob_size
field. Note that theob_size
field may later be used for other purposes. For example,int
instances use the bits ofob_size
in an implementation-defined way; the underlying storage and its size should be accessed usingPyLong_Export()
.Note
The
ob_size
field should be accessed using thePy_SIZE()
andPy_SET_SIZE()
macros.Also, the presence of an
ob_size
field in the instance layout doesn’t mean that the instance structure is variable-length. For example, thelist
type has fixed-length instances, yet those instances have aob_size
field. (As withint
, avoid reading lists’ob_size
directly. CallPyList_Size()
instead.)The
tp_basicsize
includes size needed for data of the type’stp_base
, plus any extra data needed by each instance.The correct way to set
tp_basicsize
is to use thesizeof
operator on the struct used to declare the instance layout. This struct must include the struct used to declare the base type. In other words,tp_basicsize
must be greater than or equal to the base’stp_basicsize
.Since every type is a subtype of
object
, this struct must includePyObject
orPyVarObject
(depending on whetherob_size
should be included). These are usually defined by the macroPyObject_HEAD
orPyObject_VAR_HEAD
, respectively.The basic size does not include the GC header size, as that header is not part of
PyObject_HEAD
.For cases where struct used to declare the base type is unknown, see
PyType_Spec.basicsize
andPyType_FromMetaclass()
.Notes about alignment:
tp_basicsize
must be a multiple of_Alignof(PyObject)
. When usingsizeof
on astruct
that includesPyObject_HEAD
, as recommended, the compiler ensures this. When not using a Cstruct
, or when using compiler extensions like__attribute__((packed))
, it is up to you.If the variable items require a particular alignment,
tp_basicsize
andtp_itemsize
must each be a multiple of that alignment. For example, if a type’s variable part stores adouble
, it is your responsibility that both fields are a multiple of_Alignof(double)
.
Inheritance:
These fields are inherited separately by subtypes. (That is, if the field is set to zero,
PyType_Ready()
will copy the value from the base type, indicating that the instances do not need additional storage.)If the base type has a non-zero
tp_itemsize
, it is generally not safe to settp_itemsize
to a different non-zero value in a subtype (though this depends on the implementation of the base type).
-
destructor PyTypeObject.tp_dealloc¶
The corresponding slot ID
Py_tp_dealloc
is part of the Stable ABI.A pointer to the instance destructor function. The function signature is:
void tp_dealloc(PyObject *self);
The destructor function should remove all references which the instance owns (e.g., call
Py_CLEAR()
), free all memory buffers owned by the instance, and call the type’stp_free
function to free the object itself.If you may call functions that may set the error indicator, you must use
PyErr_GetRaisedException()
andPyErr_SetRaisedException()
to ensure you don’t clobber a preexisting error indicator (the deallocation could have occurred while processing a different error):static void foo_dealloc(foo_object *self) { PyObject *et, *ev, *etb; PyObject *exc = PyErr_GetRaisedException(); ... PyErr_SetRaisedException(exc); }
The dealloc handler itself must not raise an exception; if it hits an error case it should call
PyErr_FormatUnraisable()
to log (and clear) an unraisable exception.No guarantees are made about when an object is destroyed, except:
Python will destroy an object immediately or some time after the final reference to the object is deleted, unless its finalizer (
tp_finalize
) subsequently resurrects the object.An object will not be destroyed while it is being automatically finalized (
tp_finalize
) or automatically cleared (tp_clear
).
CPython currently destroys an object immediately from
Py_DECREF()
when the new reference count is zero, but this may change in a future version.It is recommended to call
PyObject_CallFinalizerFromDealloc()
at the beginning oftp_dealloc
to guarantee that the object is always finalized before destruction.If the type supports garbage collection (the
Py_TPFLAGS_HAVE_GC
flag is set), the destructor should callPyObject_GC_UnTrack()
before clearing any member fields.It is permissible to call
tp_clear
fromtp_dealloc
to reduce code duplication and to guarantee that the object is always cleared before destruction. Beware thattp_clear
might have already been called.If the type is heap allocated (
Py_TPFLAGS_HEAPTYPE
), the deallocator should release the owned reference to its type object (viaPy_DECREF()
) after calling the type deallocator. See the example code below.:static void foo_dealloc(PyObject *op) { foo_object *self = (foo_object *) op; PyObject_GC_UnTrack(self); Py_CLEAR(self->ref); Py_TYPE(self)->tp_free(self); }
tp_dealloc
must leave the exception status unchanged. If it needs to call something that might raise an exception, the exception state must be backed up first and restored later (after logging any exceptions withPyErr_WriteUnraisable()
).Example:
static void foo_dealloc(PyObject *self) { PyObject *exc = PyErr_GetRaisedException(); if (PyObject_CallFinalizerFromDealloc(self) < 0) { // self was resurrected. goto done; } PyTypeObject *tp = Py_TYPE(self); if (tp->tp_flags & Py_TPFLAGS_HAVE_GC) { PyObject_GC_UnTrack(self); } // Optional, but convenient to avoid code duplication. if (tp->tp_clear && tp->tp_clear(self) < 0) { PyErr_WriteUnraisable(self); } // Any additional destruction goes here. tp->tp_free(self); self = NULL; // In case PyErr_WriteUnraisable() is called below. if (tp->tp_flags & Py_TPFLAGS_HEAPTYPE) { Py_CLEAR(tp); } done: // Optional, if something was called that might have raised an // exception. if (PyErr_Occurred()) { PyErr_WriteUnraisable(self); } PyErr_SetRaisedException(exc); }
tp_dealloc
may be called from any Python thread, not just the thread which created the object (if the object becomes part of a refcount cycle, that cycle might be collected by a garbage collection on any thread). This is not a problem for Python API calls, since the thread on whichtp_dealloc
is called with an attached thread state. However, if the object being destroyed in turn destroys objects from some other C library, care should be taken to ensure that destroying those objects on the thread which calledtp_dealloc
will not violate any assumptions of the library.Inheritance:
This field is inherited by subtypes.
See also
Object Life Cycle for details about how this slot relates to other slots.
-
Py_ssize_t PyTypeObject.tp_vectorcall_offset¶
An optional offset to a per-instance function that implements calling the object using the vectorcall protocol, a more efficient alternative of the simpler
tp_call
.This field is only used if the flag
Py_TPFLAGS_HAVE_VECTORCALL
is set. If so, this must be a positive integer containing the offset in the instance of avectorcallfunc
pointer.The vectorcallfunc pointer may be
NULL
, in which case the instance behaves as ifPy_TPFLAGS_HAVE_VECTORCALL
was not set: calling the instance falls back totp_call
.Any class that sets
Py_TPFLAGS_HAVE_VECTORCALL
must also settp_call
and make sure its behaviour is consistent with the vectorcallfunc function. This can be done by setting tp_call toPyVectorcall_Call()
.Changed in version 3.8: Before version 3.8, this slot was named
tp_print
. In Python 2.x, it was used for printing to a file. In Python 3.0 to 3.7, it was unused.Changed in version 3.12: Before version 3.12, it was not recommended for mutable heap types to implement the vectorcall protocol. When a user sets
__call__
in Python code, only tp_call is updated, likely making it inconsistent with the vectorcall function. Since 3.12, setting__call__
will disable vectorcall optimization by clearing thePy_TPFLAGS_HAVE_VECTORCALL
flag.Inheritance:
This field is always inherited. However, the
Py_TPFLAGS_HAVE_VECTORCALL
flag is not always inherited. If it’s not set, then the subclass won’t use vectorcall, except whenPyVectorcall_Call()
is explicitly called.
-
getattrfunc PyTypeObject.tp_getattr¶
The corresponding slot ID
Py_tp_getattr
is part of the Stable ABI.An optional pointer to the get-attribute-string function.
This field is deprecated. When it is defined, it should point to a function that acts the same as the
tp_getattro
function, but taking a C string instead of a Python string object to give the attribute name.Inheritance:
Group:
tp_getattr
,tp_getattro
This field is inherited by subtypes together with
tp_getattro
: a subtype inherits bothtp_getattr
andtp_getattro
from its base type when the subtype’stp_getattr
andtp_getattro
are bothNULL
.
-
setattrfunc PyTypeObject.tp_setattr¶
The corresponding slot ID
Py_tp_setattr
is part of the Stable ABI.An optional pointer to the function for setting and deleting attributes.
This field is deprecated. When it is defined, it should point to a function that acts the same as the
tp_setattro
function, but taking a C string instead of a Python string object to give the attribute name.Inheritance:
Group:
tp_setattr
,tp_setattro
This field is inherited by subtypes together with
tp_setattro
: a subtype inherits bothtp_setattr
andtp_setattro
from its base type when the subtype’stp_setattr
andtp_setattro
are bothNULL
.
-
PyAsyncMethods *PyTypeObject.tp_as_async¶
Pointer to an additional structure that contains fields relevant only to objects which implement awaitable and asynchronous iterator protocols at the C-level. See Async Object Structures for details.
Added in version 3.5: Formerly known as
tp_compare
andtp_reserved
.Inheritance:
The
tp_as_async
field is not inherited, but the contained fields are inherited individually.
-
reprfunc PyTypeObject.tp_repr¶
The corresponding slot ID
Py_tp_repr
is part of the Stable ABI.An optional pointer to a function that implements the built-in function
repr()
.The signature is the same as for
PyObject_Repr()
:PyObject *tp_repr(PyObject *self);
The function must return a string or a Unicode object. Ideally, this function should return a string that, when passed to
eval()
, given a suitable environment, returns an object with the same value. If this is not feasible, it should return a string starting with'<'
and ending with'>'
from which both the type and the value of the object can be deduced.Inheritance:
This field is inherited by subtypes.
Default:
When this field is not set, a string of the form
<%s object at %p>
is returned, where%s
is replaced by the type name, and%p
by the object’s memory address.
-
PyNumberMethods *PyTypeObject.tp_as_number¶
Pointer to an additional structure that contains fields relevant only to objects which implement the number protocol. These fields are documented in Number Object Structures.
Inheritance:
The
tp_as_number
field is not inherited, but the contained fields are inherited individually.
-
PySequenceMethods *PyTypeObject.tp_as_sequence¶
Pointer to an additional structure that contains fields relevant only to objects which implement the sequence protocol. These fields are documented in Sequence Object Structures.
Inheritance:
The
tp_as_sequence
field is not inherited, but the contained fields are inherited individually.
-
PyMappingMethods *PyTypeObject.tp_as_mapping¶
Pointer to an additional structure that contains fields relevant only to objects which implement the mapping protocol. These fields are documented in Mapping Object Structures.
Inheritance:
The
tp_as_mapping
field is not inherited, but the contained fields are inherited individually.
-
hashfunc PyTypeObject.tp_hash¶
The corresponding slot ID
Py_tp_hash
is part of the Stable ABI.An optional pointer to a function that implements the built-in function
hash()
.The signature is the same as for
PyObject_Hash()
:Py_hash_t tp_hash(PyObject *);
The value
-1
should not be returned as a normal return value; when an error occurs during the computation of the hash value, the function should set an exception and return-1
.When this field is not set (and
tp_richcompare
is not set), an attempt to take the hash of the object raisesTypeError
. This is the same as setting it toPyObject_HashNotImplemented()
.This field can be set explicitly to
PyObject_HashNotImplemented()
to block inheritance of the hash method from a parent type. This is interpreted as the equivalent of__hash__ = None
at the Python level, causingisinstance(o, collections.Hashable)
to correctly returnFalse
. Note that the converse is also true - setting__hash__ = None
on a class at the Python level will result in thetp_hash
slot being set toPyObject_HashNotImplemented()
.Inheritance:
Group:
tp_hash
,tp_richcompare
This field is inherited by subtypes together with
tp_richcompare
: a subtype inherits both oftp_richcompare
andtp_hash
, when the subtype’stp_richcompare
andtp_hash
are bothNULL
.Default:
-
ternaryfunc PyTypeObject.tp_call¶
The corresponding slot ID
Py_tp_call
is part of the Stable ABI.An optional pointer to a function that implements calling the object. This should be
NULL
if the object is not callable. The signature is the same as forPyObject_Call()
:PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);
Inheritance:
This field is inherited by subtypes.
-
reprfunc PyTypeObject.tp_str¶
The corresponding slot ID
Py_tp_str
is part of the Stable ABI.An optional pointer to a function that implements the built-in operation
str()
. (Note thatstr
is a type now, andstr()
calls the constructor for that type. This constructor callsPyObject_Str()
to do the actual work, andPyObject_Str()
will call this handler.)The signature is the same as for
PyObject_Str()
:PyObject *tp_str(PyObject *self);
The function must return a string or a Unicode object. It should be a “friendly” string representation of the object, as this is the representation that will be used, among other things, by the
print()
function.Inheritance:
This field is inherited by subtypes.
Default:
When this field is not set,
PyObject_Repr()
is called to return a string representation.
-
getattrofunc PyTypeObject.tp_getattro¶
The corresponding slot ID
Py_tp_getattro
is part of the Stable ABI.An optional pointer to the get-attribute function.
The signature is the same as for
PyObject_GetAttr()
:PyObject *tp_getattro(PyObject *self, PyObject *attr);
It is usually convenient to set this field to
PyObject_GenericGetAttr()
, which implements the normal way of looking for object attributes.Inheritance:
Group:
tp_getattr
,tp_getattro
This field is inherited by subtypes together with
tp_getattr
: a subtype inherits bothtp_getattr
andtp_getattro
from its base type when the subtype’stp_getattr
andtp_getattro
are bothNULL
.Default:
-
setattrofunc PyTypeObject.tp_setattro¶
The corresponding slot ID
Py_tp_setattro
is part of the Stable ABI.An optional pointer to the function for setting and deleting attributes.
The signature is the same as for
PyObject_SetAttr()
:int tp_setattro(PyObject *self, PyObject *attr, PyObject *value);
In addition, setting value to
NULL
to delete an attribute must be supported. It is usually convenient to set this field toPyObject_GenericSetAttr()
, which implements the normal way of setting object attributes.Inheritance:
Group:
tp_setattr
,tp_setattro
This field is inherited by subtypes together with
tp_setattr
: a subtype inherits bothtp_setattr
andtp_setattro
from its base type when the subtype’stp_setattr
andtp_setattro
are bothNULL
.Default:
-
PyBufferProcs *PyTypeObject.tp_as_buffer¶
Pointer to an additional structure that contains fields relevant only to objects which implement the buffer interface. These fields are documented in Buffer Object Structures.
Inheritance:
The
tp_as_buffer
field is not inherited, but the contained fields are inherited individually.
-
unsigned long PyTypeObject.tp_flags¶
This field is a bit mask of various flags. Some flags indicate variant semantics for certain situations; others are used to indicate that certain fields in the type object (or in the extension structures referenced via
tp_as_number
,tp_as_sequence
,tp_as_mapping
, andtp_as_buffer
) that were historically not always present are valid; if such a flag bit is clear, the type fields it guards must not be accessed and must be considered to have a zero orNULL
value instead.Inheritance:
Inheritance of this field is complicated. Most flag bits are inherited individually, i.e. if the base type has a flag bit set, the subtype inherits this flag bit. The flag bits that pertain to extension structures are strictly inherited if the extension structure is inherited, i.e. the base type’s value of the flag bit is copied into the subtype together with a pointer to the extension structure. The
Py_TPFLAGS_HAVE_GC
flag bit is inherited together with thetp_traverse
andtp_clear
fields, i.e. if thePy_TPFLAGS_HAVE_GC
flag bit is clear in the subtype and thetp_traverse
andtp_clear
fields in the subtype exist and haveNULL
values.Default:
PyBaseObject_Type
usesPy_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
.Bit Masks:
The following bit masks are currently defined; these can be ORed together using the
|
operator to form the value of thetp_flags
field. The macroPyType_HasFeature()
takes a type and a flags value, tp and f, and checks whethertp->tp_flags & f
is non-zero.-
Py_TPFLAGS_HEAPTYPE¶
This bit is set when the type object itself is allocated on the heap, for example, types created dynamically using
PyType_FromSpec()
. In this case, theob_type
field of its instances is considered a reference to the type, and the type object is INCREF’ed when a new instance is created, and DECREF’ed when an instance is destroyed (this does not apply to instances of subtypes; only the type referenced by the instance’s ob_type gets INCREF’ed or DECREF’ed). Heap types should also support garbage collection as they can form a reference cycle with their own module object.Inheritance:
???
-
Py_TPFLAGS_BASETYPE¶
- Part of the Stable ABI.
This bit is set when the type can be used as the base type of another type. If this bit is clear, the type cannot be subtyped (similar to a “final” class in Java).
Inheritance:
???
-
Py_TPFLAGS_READY¶
This bit is set when the type object has been fully initialized by
PyType_Ready()
.Inheritance:
???
-
Py_TPFLAGS_READYING¶
This bit is set while
PyType_Ready()
is in the process of initializing the type object.Inheritance:
???
-
Py_TPFLAGS_HAVE_GC¶
- Part of the Stable ABI.
This bit is set when the object supports garbage collection. If this bit is set, memory for new instances (see
tp_alloc
) must be allocated usingPyObject_GC_New
orPyType_GenericAlloc()
and deallocated (seetp_free
) usingPyObject_GC_Del()
. More information in section Supporting Cyclic Garbage Collection.Inheritance:
Group:
Py_TPFLAGS_HAVE_GC
,tp_traverse
,tp_clear
The
Py_TPFLAGS_HAVE_GC
flag bit is inherited together with thetp_traverse
andtp_clear
fields, i.e. if thePy_TPFLAGS_HAVE_GC
flag bit is clear in the subtype and thetp_traverse
andtp_clear
fields in the subtype exist and haveNULL
values.
-
Py_TPFLAGS_DEFAULT¶
- Part of the Stable ABI.
This is a bitmask of all the bits that pertain to the existence of certain fields in the type object and its extension structures. Currently, it includes the following bits:
Py_TPFLAGS_HAVE_STACKLESS_EXTENSION
.Inheritance:
???
-
Py_TPFLAGS_METHOD_DESCRIPTOR¶
- Part of the Stable ABI since version 3.8.
This bit indicates that objects behave like unbound methods.
If this flag is set for
type(meth)
, then:meth.__get__(obj, cls)(*args, **kwds)
(withobj
not None) must be equivalent tometh(obj, *args, **kwds)
.meth.__get__(None, cls)(*args, **kwds)
must be equivalent tometh(*args, **kwds)
.
This flag enables an optimization for typical method calls like
obj.meth()
: it avoids creating a temporary “bound method” object forobj.meth
.Added in version 3.8.
Inheritance:
This flag is never inherited by types without the
Py_TPFLAGS_IMMUTABLETYPE
flag set. For extension types, it is inherited whenevertp_descr_get
is inherited.
-
Py_TPFLAGS_MANAGED_DICT¶
This bit indicates that instances of the class have a
__dict__
attribute, and that the space for the dictionary is managed by the VM.If this flag is set,
Py_TPFLAGS_HAVE_GC
should also be set.The type traverse function must call
PyObject_VisitManagedDict()
and its clear function must callPyObject_ClearManagedDict()
.Added in version 3.12.
Inheritance:
This flag is inherited unless the
tp_dictoffset
field is set in a superclass.
-
Py_TPFLAGS_MANAGED_WEAKREF¶
This bit indicates that instances of the class should be weakly referenceable.
Added in version 3.12.
Inheritance:
This flag is inherited unless the
tp_weaklistoffset
field is set in a superclass.
-
Py_TPFLAGS_ITEMS_AT_END¶
- Part of the Stable ABI since version 3.12.
Only usable with variable-size types, i.e. ones with non-zero
tp_itemsize
.Indicates that the variable-sized portion of an instance of this type is at the end of the instance’s memory area, at an offset of
Py_TYPE(obj)->tp_basicsize
(which may be different in each subclass).When setting this flag, be sure that all superclasses either use this memory layout, or are not variable-sized. Python does not check this.
Added in version 3.12.
Inheritance:
This flag is inherited.
-
Py_TPFLAGS_LONG_SUBCLASS¶
-
Py_TPFLAGS_LIST_SUBCLASS¶
-
Py_TPFLAGS_TUPLE_SUBCLASS¶
-
Py_TPFLAGS_BYTES_SUBCLASS¶
-
Py_TPFLAGS_UNICODE_SUBCLASS¶
-
Py_TPFLAGS_DICT_SUBCLASS¶
-
Py_TPFLAGS_BASE_EXC_SUBCLASS¶
-
Py_TPFLAGS_TYPE_SUBCLASS¶
Functions such as
PyLong_Check()
will callPyType_FastSubclass()
with one of these flags to quickly determine if a type is a subclass of a built-in type; such specific checks are faster than a generic check, likePyObject_IsInstance()
. Custom types that inherit from built-ins should have theirtp_flags
set appropriately, or the code that interacts with such types will behave differently depending on what kind of check is used.
-
Py_TPFLAGS_HAVE_FINALIZE¶
This bit is set when the
tp_finalize
slot is present in the type structure.Added in version 3.4.
Deprecated since version 3.8: This flag isn’t necessary anymore, as the interpreter assumes the
tp_finalize
slot is always present in the type structure.
-
Py_TPFLAGS_HAVE_VECTORCALL¶
- Part of the Stable ABI since version 3.12.
This bit is set when the class implements the vectorcall protocol. See
tp_vectorcall_offset
for details.Inheritance:
This bit is inherited if
tp_call
is also inherited.Added in version 3.8: as
_Py_TPFLAGS_HAVE_VECTORCALL
Changed in version 3.9.
Renamed to the current name, without the leading underscore. The old provisional name is soft deprecated.
Changed in version 3.12: This flag is now removed from a class when the class’s
__call__()
method is reassigned.This flag can now be inherited by mutable classes.
-
Py_TPFLAGS_IMMUTABLETYPE¶
This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.
PyType_Ready()
automatically applies this flag to static types.Inheritance:
This flag is not inherited.
Added in version 3.10.
-
Py_TPFLAGS_DISALLOW_INSTANTIATION¶
Disallow creating instances of the type: set
tp_new
to NULL and don’t create the__new__
key in the type dictionary.The flag must be set before creating the type, not after. For example, it must be set before
PyType_Ready()
is called on the type.The flag is set automatically on static types if
tp_base
is NULL or&PyBaseObject_Type
andtp_new
is NULL.Inheritance:
This flag is not inherited. However, subclasses will not be instantiable unless they provide a non-NULL
tp_new
(which is only possible via the C API).Note
To disallow instantiating a class directly but allow instantiating its subclasses (e.g. for an abstract base class), do not use this flag. Instead, make
tp_new
only succeed for subclasses.Added in version 3.10.
-
Py_TPFLAGS_MAPPING¶
This bit indicates that instances of the class may match mapping patterns when used as the subject of a
match
block. It is automatically set when registering or subclassingcollections.abc.Mapping
, and unset when registeringcollections.abc.Sequence
.Note
Py_TPFLAGS_MAPPING
andPy_TPFLAGS_SEQUENCE
are mutually exclusive; it is an error to enable both flags simultaneously.Inheritance:
This flag is inherited by types that do not already set
Py_TPFLAGS_SEQUENCE
.See also
PEP 634 – Structural Pattern Matching: Specification
Added in version 3.10.
-
Py_TPFLAGS_SEQUENCE¶
This bit indicates that instances of the class may match sequence patterns when used as the subject of a
match
block. It is automatically set when registering or subclassingcollections.abc.Sequence
, and unset when registeringcollections.abc.Mapping
.Note
Py_TPFLAGS_MAPPING
andPy_TPFLAGS_SEQUENCE
are mutually exclusive; it is an error to enable both flags simultaneously.Inheritance:
This flag is inherited by types that do not already set
Py_TPFLAGS_MAPPING
.See also
PEP 634 – Structural Pattern Matching: Specification
Added in version 3.10.
-
Py_TPFLAGS_VALID_VERSION_TAG¶
Internal. Do not set or unset this flag. To indicate that a class has changed call
PyType_Modified()
Warning
This flag is present in header files, but is not be used. It will be removed in a future version of CPython
-
Py_TPFLAGS_HEAPTYPE¶
-
const char *PyTypeObject.tp_doc¶
The corresponding slot ID
Py_tp_doc
is part of the Stable ABI.An optional pointer to a NUL-terminated C string giving the docstring for this type object. This is exposed as the
__doc__
attribute on the type and instances of the type.Inheritance:
This field is not inherited by subtypes.
-
traverseproc PyTypeObject.tp_traverse¶
The corresponding slot ID
Py_tp_traverse
is part of the Stable ABI.An optional pointer to a traversal function for the garbage collector. This is only used if the
Py_TPFLAGS_HAVE_GC
flag bit is set. The signature is:int tp_traverse(PyObject *self, visitproc visit, void *arg);
More information about Python’s garbage collection scheme can be found in section Supporting Cyclic Garbage Collection.
The
tp_traverse
pointer is used by the garbage collector to detect reference cycles. A typical implementation of atp_traverse
function simply callsPy_VISIT()
on each of the instance’s members that are Python objects that the instance owns. For example, this is functionlocal_traverse()
from the_thread
extension module:static int local_traverse(PyObject *op, visitproc visit, void *arg) { localobject *self = (localobject *) op; Py_VISIT(self->args); Py_VISIT(self->kw); Py_VISIT(self->dict); return 0; }
Note that
Py_VISIT()
is called only on those members that can participate in reference cycles. Although there is also aself->key
member, it can only beNULL
or a Python string and therefore cannot be part of a reference cycle.On the other hand, even if you know a member can never be part of a cycle, as a debugging aid you may want to visit it anyway just so the
gc
module’sget_referents()
function will include it.Heap types (
Py_TPFLAGS_HEAPTYPE
) must visit their type with:Py_VISIT(Py_TYPE(self));
It is only needed since Python 3.9. To support Python 3.8 and older, this line must be conditional:
#if PY_VERSION_HEX >= 0x03090000 Py_VISIT(Py_TYPE(self)); #endif
If the
Py_TPFLAGS_MANAGED_DICT
bit is set in thetp_flags
field, the traverse function must callPyObject_VisitManagedDict()
like this:PyObject_VisitManagedDict((PyObject*)self, visit, arg);
Warning
When implementing
tp_traverse
, only the members that the instance owns (by having strong references to them) must be visited. For instance, if an object supports weak references via thetp_weaklist
slot, the pointer supporting the linked list (what tp_weaklist points to) must not be visited as the instance does not directly own the weak references to itself (the weakreference list is there to support the weak reference machinery, but the instance has no strong reference to the elements inside it, as they are allowed to be removed even if the instance is still alive).Warning
The traversal function must not have any side effects. It must not modify the reference counts of any Python objects nor create or destroy any Python objects.
Note that
Py_VISIT()
requires the visit and arg parameters tolocal_traverse()
to have these specific names; don’t name them just anything.Instances of heap-allocated types hold a reference to their type. Their traversal function must therefore either visit
Py_TYPE(self)
, or delegate this responsibility by callingtp_traverse
of another heap-allocated type (such as a heap-allocated superclass). If they do not, the type object may not be garbage-collected.Note
The
tp_traverse
function can be called from any thread.Changed in version 3.9: Heap-allocated types are expected to visit
Py_TYPE(self)
intp_traverse
. In earlier versions of Python, due to bug 40217, doing this may lead to crashes in subclasses.Inheritance:
Group:
Py_TPFLAGS_HAVE_GC
,tp_traverse
,tp_clear
This field is inherited by subtypes together with
tp_clear
and thePy_TPFLAGS_HAVE_GC
flag bit: the flag bit,tp_traverse
, andtp_clear
are all inherited from the base type if they are all zero in the subtype.
-
inquiry PyTypeObject.tp_clear¶
The corresponding slot ID
Py_tp_clear
is part of the Stable ABI.An optional pointer to a clear function. The signature is:
int tp_clear(PyObject *);
The purpose of this function is to break reference cycles that are causing a cyclic isolate so that the objects can be safely destroyed. A cleared object is a partially destroyed object; the object is not obligated to satisfy design invariants held during normal use.
tp_clear
does not need to delete references to objects that can’t participate in reference cycles, such as Python strings or Python integers. However, it may be convenient to clear all references, and write the type’stp_dealloc
function to invoketp_clear
to avoid code duplication. (Beware thattp_clear
might have already been called. Prefer calling idempotent functions likePy_CLEAR()
.)Any non-trivial cleanup should be performed in
tp_finalize
instead oftp_clear
.Note
If
tp_clear
fails to break a reference cycle then the objects in the cyclic isolate may remain indefinitely uncollectable (“leak”). Seegc.garbage
.Note
Referents (direct and indirect) might have already been cleared; they are not guaranteed to be in a consistent state.
Note
The
tp_clear
function can be called from any thread.Note
An object is not guaranteed to be automatically cleared before its destructor (
tp_dealloc
) is called.This function differs from the destructor (
tp_dealloc
) in the following ways:The purpose of clearing an object is to remove references to other objects that might participate in a reference cycle. The purpose of the destructor, on the other hand, is a superset: it must release all resources it owns, including references to objects that cannot participate in a reference cycle (e.g., integers) as well as the object’s own memory (by calling
tp_free
).When
tp_clear
is called, other objects might still hold references to the object being cleared. Because of this,tp_clear
must not deallocate the object’s own memory (tp_free
). The destructor, on the other hand, is only called when no (strong) references exist, and as such, must safely destroy the object itself by deallocating it.tp_clear
might never be automatically called. An object’s destructor, on the other hand, will be automatically called some time after the object becomes unreachable (i.e., either there are no references to the object or the object is a member of a cyclic isolate).
No guarantees are made about when, if, or how often Python automatically clears an object, except:
Python will not automatically clear an object if it is reachable, i.e., there is a reference to it and it is not a member of a cyclic isolate.
Python will not automatically clear an object if it has not been automatically finalized (see
tp_finalize
). (If the finalizer resurrected the object, the object may or may not be automatically finalized again before it is cleared.)If an object is a member of a cyclic isolate, Python will not automatically clear it if any member of the cyclic isolate has not yet been automatically finalized (
tp_finalize
).Python will not destroy an object until after any automatic calls to its
tp_clear
function have returned. This ensures that the act of breaking a reference cycle does not invalidate theself
pointer whiletp_clear
is still executing.Python will not automatically call
tp_clear
multiple times concurrently.
CPython currently only automatically clears objects as needed to break reference cycles in a cyclic isolate, but future versions might clear objects regularly before their destruction.
Taken together, all
tp_clear
functions in the system must combine to break all reference cycles. This is subtle, and if in any doubt supply atp_clear
function. For example, the tuple type does not implement atp_clear
function, because it’s possible to prove that no reference cycle can be composed entirely of tuples. Therefore thetp_clear
functions of other types are responsible for breaking any cycle containing a tuple. This isn’t immediately obvious, and there’s rarely a good reason to avoid implementingtp_clear
.Implementations of
tp_clear
should drop the instance’s references to those of its members that may be Python objects, and set its pointers to those members toNULL
, as in the following example:static int local_clear(PyObject *op) { localobject *self = (localobject *) op; Py_CLEAR(self->key); Py_CLEAR(self->args); Py_CLEAR(self->kw); Py_CLEAR(self->dict); return 0; }
The
Py_CLEAR()
macro should be used, because clearing references is delicate: the reference to the contained object must not be released (viaPy_DECREF()
) until after the pointer to the contained object is set toNULL
. This is because releasing the reference may cause the contained object to become trash, triggering a chain of reclamation activity that may include invoking arbitrary Python code (due to finalizers, or weakref callbacks, associated with the contained object). If it’s possible for such code to reference self again, it’s important that the pointer to the contained object beNULL
at that time, so that self knows the contained object can no longer be used. ThePy_CLEAR()
macro performs the operations in a safe order.If the
Py_TPFLAGS_MANAGED_DICT
bit is set in thetp_flags
field, the clear function must callPyObject_ClearManagedDict()
like this:PyObject_ClearManagedDict((PyObject*)self);
More information about Python’s garbage collection scheme can be found in section Supporting Cyclic Garbage Collection.
Inheritance:
Group:
Py_TPFLAGS_HAVE_GC
,tp_traverse
,tp_clear
This field is inherited by subtypes together with
tp_traverse
and thePy_TPFLAGS_HAVE_GC
flag bit: the flag bit,tp_traverse
, andtp_clear
are all inherited from the base type if they are all zero in the subtype.See also
Object Life Cycle for details about how this slot relates to other slots.
-
richcmpfunc PyTypeObject.tp_richcompare¶
The corresponding slot ID
Py_tp_richcompare
is part of the Stable ABI.An optional pointer to the rich comparison function, whose signature is:
PyObject *tp_richcompare(PyObject *self, PyObject *other, int op);
The first parameter is guaranteed to be an instance of the type that is defined by
PyTypeObject
.The function should return the result of the comparison (usually
Py_True
orPy_False
). If the comparison is undefined, it must returnPy_NotImplemented
, if another error occurred it must returnNULL
and set an exception condition.The following constants are defined to be used as the third argument for
tp_richcompare
and forPyObject_RichCompare()
:Constant
Comparison
-
Py_LT¶
<
-
Py_LE¶
<=
-
Py_EQ¶
==
-
Py_NE¶
!=
-
Py_GT¶
>
-
Py_GE¶
>=
The following macro is defined to ease writing rich comparison functions:
-
Py_RETURN_RICHCOMPARE(VAL_A, VAL_B, op)¶
Return
Py_True
orPy_False
from the function, depending on the result of a comparison. VAL_A and VAL_B must be orderable by C comparison operators (for example, they may be C ints or floats). The third argument specifies the requested operation, as forPyObject_RichCompare()
.The returned value is a new strong reference.
On error, sets an exception and returns
NULL
from the function.Added in version 3.7.
Inheritance:
Group:
tp_hash
,tp_richcompare
This field is inherited by subtypes together with
tp_hash
: a subtype inheritstp_richcompare
andtp_hash
when the subtype’stp_richcompare
andtp_hash
are bothNULL
.Default:
PyBaseObject_Type
provides atp_richcompare
implementation, which may be inherited. However, if onlytp_hash
is defined, not even the inherited function is used and instances of the type will not be able to participate in any comparisons.-
Py_LT¶
-
Py_ssize_t PyTypeObject.tp_weaklistoffset¶
While this field is still supported,
Py_TPFLAGS_MANAGED_WEAKREF
should be used instead, if at all possible.If the instances of this type are weakly referenceable, this field is greater than zero and contains the offset in the instance structure of the weak reference list head (ignoring the GC header, if present); this offset is used by
PyObject_ClearWeakRefs()
and thePyWeakref_*
functions. The instance structure needs to include a field of type PyObject* which is initialized toNULL
.Do not confuse this field with
tp_weaklist
; that is the list head for weak references to the type object itself.It is an error to set both the
Py_TPFLAGS_MANAGED_WEAKREF
bit andtp_weaklistoffset
.Inheritance:
This field is inherited by subtypes, but see the rules listed below. A subtype may override this offset; this means that the subtype uses a different weak reference list head than the base type. Since the list head is always found via
tp_weaklistoffset
, this should not be a problem.Default:
If the
Py_TPFLAGS_MANAGED_WEAKREF
bit is set in thetp_flags
field, thentp_weaklistoffset
will be set to a negative value, to indicate that it is unsafe to use this field.
-
getiterfunc PyTypeObject.tp_iter¶
The corresponding slot ID
Py_tp_iter
is part of the Stable ABI.An optional pointer to a function that returns an iterator for the object. Its presence normally signals that the instances of this type are iterable (although sequences may be iterable without this function).
This function has the same signature as
PyObject_GetIter()
:PyObject *tp_iter(PyObject *self);
Inheritance:
This field is inherited by subtypes.
-
iternextfunc PyTypeObject.tp_iternext¶
The corresponding slot ID
Py_tp_iternext
is part of the Stable ABI.An optional pointer to a function that returns the next item in an iterator. The signature is:
PyObject *tp_iternext(PyObject *self);
When the iterator is exhausted, it must return
NULL
; aStopIteration
exception may or may not be set. When another error occurs, it must returnNULL
too. Its presence signals that the instances of this type are iterators.Iterator types should also define the
tp_iter
function, and that function should return the iterator instance itself (not a new iterator instance).This function has the same signature as
PyIter_Next()
.Inheritance:
This field is inherited by subtypes.
-
struct PyMethodDef *PyTypeObject.tp_methods¶
The corresponding slot ID
Py_tp_methods
is part of the Stable ABI.An optional pointer to a static
NULL
-terminated array ofPyMethodDef
structures, declaring regular methods of this type.For each entry in the array, an entry is added to the type’s dictionary (see
tp_dict
below) containing a method descriptor.Inheritance:
This field is not inherited by subtypes (methods are inherited through a different mechanism).
-
struct PyMemberDef *PyTypeObject.tp_members¶
The corresponding slot ID
Py_tp_members
is part of the Stable ABI.An optional pointer to a static
NULL
-terminated array ofPyMemberDef
structures, declaring regular data members (fields or slots) of instances of this type.For each entry in the array, an entry is added to the type’s dictionary (see
tp_dict
below) containing a member descriptor.Inheritance:
This field is not inherited by subtypes (members are inherited through a different mechanism).
-
struct PyGetSetDef *PyTypeObject.tp_getset¶
The corresponding slot ID
Py_tp_getset
is part of the Stable ABI.An optional pointer to a static
NULL
-terminated array ofPyGetSetDef
structures, declaring computed attributes of instances of this type.For each entry in the array, an entry is added to the type’s dictionary (see
tp_dict
below) containing a getset descriptor.Inheritance:
This field is not inherited by subtypes (computed attributes are inherited through a different mechanism).
-
PyTypeObject *PyTypeObject.tp_base¶
The corresponding slot ID
Py_tp_base
is part of the Stable ABI.An optional pointer to a base type from which type properties are inherited. At this level, only single inheritance is supported; multiple inheritance require dynamically creating a type object by calling the metatype.
Note
Slot initialization is subject to the rules of initializing globals. C99 requires the initializers to be “address constants”. Function designators like
PyType_GenericNew()
, with implicit conversion to a pointer, are valid C99 address constants.However, the unary ‘&’ operator applied to a non-static variable like
PyBaseObject_Type
is not required to produce an address constant. Compilers may support this (gcc does), MSVC does not. Both compilers are strictly standard conforming in this particular behavior.Consequently,
tp_base
should be set in the extension module’s init function.Inheritance:
This field is not inherited by subtypes (obviously).
Default:
This field defaults to
&PyBaseObject_Type
(which to Python programmers is known as the typeobject
).
-
PyObject *PyTypeObject.tp_dict¶
The type’s dictionary is stored here by
PyType_Ready()
.This field should normally be initialized to
NULL
before PyType_Ready is called; it may also be initialized to a dictionary containing initial attributes for the type. OncePyType_Ready()
has initialized the type, extra attributes for the type may be added to this dictionary only if they don’t correspond to overloaded operations (like__add__()
). Once initialization for the type has finished, this field should be treated as read-only.Some types may not store their dictionary in this slot. Use
PyType_GetDict()
to retrieve the dictionary for an arbitrary type.Changed in version 3.12: Internals detail: For static builtin types, this is always
NULL
. Instead, the dict for such types is stored onPyInterpreterState
. UsePyType_GetDict()
to get the dict for an arbitrary type.Inheritance:
This field is not inherited by subtypes (though the attributes defined in here are inherited through a different mechanism).
Default:
If this field is
NULL
,PyType_Ready()
will assign a new dictionary to it.Warning
It is not safe to use
PyDict_SetItem()
on or otherwise modifytp_dict
with the dictionary C-API.
-
descrgetfunc PyTypeObject.tp_descr_get¶
The corresponding slot ID
Py_tp_descr_get
is part of the Stable ABI.An optional pointer to a “descriptor get” function.
The function signature is:
PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);
Inheritance:
This field is inherited by subtypes.
-
descrsetfunc PyTypeObject.tp_descr_set¶
The corresponding slot ID
Py_tp_descr_set
is part of the Stable ABI.An optional pointer to a function for setting and deleting a descriptor’s value.
The function signature is:
int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);
The value argument is set to
NULL
to delete the value.Inheritance:
This field is inherited by subtypes.
-
Py_ssize_t PyTypeObject.tp_dictoffset¶
While this field is still supported,
Py_TPFLAGS_MANAGED_DICT
should be used instead, if at all possible.If the instances of this type have a dictionary containing instance variables, this field is non-zero and contains the offset in the instances of the type of the instance variable dictionary; this offset is used by
PyObject_GenericGetAttr()
.Do not confuse this field with
tp_dict
; that is the dictionary for attributes of the type object itself.The value specifies the offset of the dictionary from the start of the instance structure.
The
tp_dictoffset
should be regarded as write-only. To get the pointer to the dictionary callPyObject_GenericGetDict()
. CallingPyObject_GenericGetDict()
may need to allocate memory for the dictionary, so it is may be more efficient to callPyObject_GetAttr()
when accessing an attribute on the object.It is an error to set both the
Py_TPFLAGS_MANAGED_DICT
bit andtp_dictoffset
.Inheritance:
This field is inherited by subtypes. A subtype should not override this offset; doing so could be unsafe, if C code tries to access the dictionary at the previous offset. To properly support inheritance, use
Py_TPFLAGS_MANAGED_DICT
.Default:
This slot has no default. For static types, if the field is
NULL
then no__dict__
gets created for instances.If the
Py_TPFLAGS_MANAGED_DICT
bit is set in thetp_flags
field, thentp_dictoffset
will be set to-1
, to indicate that it is unsafe to use this field.
-
initproc PyTypeObject.tp_init¶
The corresponding slot ID
Py_tp_init
is part of the Stable ABI.An optional pointer to an instance initialization function.
This function corresponds to the
__init__()
method of classes. Like__init__()
, it is possible to create an instance without calling__init__()
, and it is possible to reinitialize an instance by calling its__init__()
method again.The function signature is:
int tp_init(PyObject *self, PyObject *args, PyObject *kwds);
The self argument is the instance to be initialized; the args and kwds arguments represent positional and keyword arguments of the call to
__init__()
.The
tp_init
function, if notNULL
, is called when an instance is created normally by calling its type, after the type’stp_new
function has returned an instance of the type. If thetp_new
function returns an instance of some other type that is not a subtype of the original type, notp_init
function is called; iftp_new
returns an instance of a subtype of the original type, the subtype’stp_init
is called.Returns
0
on success,-1
and sets an exception on error.Inheritance:
This field is inherited by subtypes.
Default:
For static types this field does not have a default.
-
allocfunc PyTypeObject.tp_alloc¶
The corresponding slot ID
Py_tp_alloc
is part of the Stable ABI.An optional pointer to an instance allocation function.
The function signature is:
PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);
Inheritance:
Static subtypes inherit this slot, which will be
PyType_GenericAlloc()
if inherited fromobject
.Heap subtypes do not inherit this slot.
Default:
For heap subtypes, this field is always set to
PyType_GenericAlloc()
.For static subtypes, this slot is inherited (see above).
-
newfunc PyTypeObject.tp_new¶
The corresponding slot ID
Py_tp_new
is part of the Stable ABI.An optional pointer to an instance creation function.
The function signature is:
PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds);
The subtype argument is the type of the object being created; the args and kwds arguments represent positional and keyword arguments of the call to the type. Note that subtype doesn’t have to equal the type whose
tp_new
function is called; it may be a subtype of that type (but not an unrelated type).The
tp_new
function should callsubtype->tp_alloc(subtype, nitems)
to allocate space for the object, and then do only as much further initialization as is absolutely necessary. Initialization that can safely be ignored or repeated should be placed in thetp_init
handler. A good rule of thumb is that for immutable types, all initialization should take place intp_new
, while for mutable types, most initialization should be deferred totp_init
.Set the
Py_TPFLAGS_DISALLOW_INSTANTIATION
flag to disallow creating instances of the type in Python.Inheritance:
This field is inherited by subtypes, except it is not inherited by static types whose
tp_base
isNULL
or&PyBaseObject_Type
.Default:
For static types this field has no default. This means if the slot is defined as
NULL
, the type cannot be called to create new instances; presumably there is some other way to create instances, like a factory function.
-
freefunc PyTypeObject.tp_free¶
The corresponding slot ID
Py_tp_free
is part of the Stable ABI.An optional pointer to an instance deallocation function. Its signature is:
void tp_free(void *self);
This function must free the memory allocated by
tp_alloc
.Inheritance:
Static subtypes inherit this slot, which will be
PyObject_Free()
if inherited fromobject
. Exception: If the type supports garbage collection (i.e., thePy_TPFLAGS_HAVE_GC
flag is set intp_flags
) and it would inheritPyObject_Free()
, then this slot is not inherited but instead defaults toPyObject_GC_Del()
.Heap subtypes do not inherit this slot.
Default:
For heap subtypes, this slot defaults to a deallocator suitable to match
PyType_GenericAlloc()
and the value of thePy_TPFLAGS_HAVE_GC
flag.For static subtypes, this slot is inherited (see above).
-
inquiry PyTypeObject.tp_is_gc¶
The corresponding slot ID
Py_tp_is_gc
is part of the Stable ABI.An optional pointer to a function called by the garbage collector.
The garbage collector needs to know whether a particular object is collectible or not. Normally, it is sufficient to look at the object’s type’s
tp_flags
field, and check thePy_TPFLAGS_HAVE_GC
flag bit. But some types have a mixture of statically and dynamically allocated instances, and the statically allocated instances are not collectible. Such types should define this function; it should return1
for a collectible instance, and0
for a non-collectible instance. The signature is:int tp_is_gc(PyObject *self);
(The only example of this are types themselves. The metatype,
PyType_Type
, defines this function to distinguish between statically and dynamically allocated types.)Inheritance:
This field is inherited by subtypes.
Default:
This slot has no default. If this field is
NULL
,Py_TPFLAGS_HAVE_GC
is used as the functional equivalent.
-
PyObject *PyTypeObject.tp_bases¶
The corresponding slot ID
Py_tp_bases
is part of the Stable ABI.Tuple of base types.
This field should be set to
NULL
and treated as read-only. Python will fill it in when the type isinitialized
.For dynamically created classes, the
Py_tp_bases
slot
can be used instead of the bases argument ofPyType_FromSpecWithBases()
. The argument form is preferred.Warning
Multiple inheritance does not work well for statically defined types. If you set
tp_bases
to a tuple, Python will not raise an error, but some slots will only be inherited from the first base.Inheritance:
This field is not inherited.
-
PyObject *PyTypeObject.tp_mro¶
Tuple containing the expanded set of base types, starting with the type itself and ending with
object
, in Method Resolution Order.This field should be set to
NULL
and treated as read-only. Python will fill it in when the type isinitialized
.Inheritance:
This field is not inherited; it is calculated fresh by
PyType_Ready()
.
-
PyObject *PyTypeObject.tp_cache¶
Unused. Internal use only.
Inheritance:
This field is not inherited.
-
void *PyTypeObject.tp_subclasses¶
A collection of subclasses. Internal use only. May be an invalid pointer.
To get a list of subclasses, call the Python method
__subclasses__()
.Changed in version 3.12: For some types, this field does not hold a valid PyObject*. The type was changed to void* to indicate this.
Inheritance:
This field is not inherited.
-
PyObject *PyTypeObject.tp_weaklist¶
Weak reference list head, for weak references to this type object. Not inherited. Internal use only.
Changed in version 3.12: Internals detail: For the static builtin types this is always
NULL
, even if weakrefs are added. Instead, the weakrefs for each are stored onPyInterpreterState
. Use the public C-API or the internal_PyObject_GET_WEAKREFS_LISTPTR()
macro to avoid the distinction.Inheritance:
This field is not inherited.
-
destructor PyTypeObject.tp_del¶
The corresponding slot ID
Py_tp_del
is part of the Stable ABI.This field is deprecated. Use
tp_finalize
instead.
-
unsigned int PyTypeObject.tp_version_tag¶
Used to index into the method cache. Internal use only.
Inheritance:
This field is not inherited.
-
destructor PyTypeObject.tp_finalize¶
The corresponding slot ID
Py_tp_finalize
is part of the Stable ABI since version 3.5.An optional pointer to an instance finalization function. This is the C implementation of the
__del__()
special method. Its signature is:void tp_finalize(PyObject *self);
The primary purpose of finalization is to perform any non-trivial cleanup that must be performed before the object is destroyed, while the object and any other objects it directly or indirectly references are still in a consistent state. The finalizer is allowed to execute arbitrary Python code.
Before Python automatically finalizes an object, some of the object’s direct or indirect referents might have themselves been automatically finalized. However, none of the referents will have been automatically cleared (
tp_clear
) yet.Other non-finalized objects might still be using a finalized object, so the finalizer must leave the object in a sane state (e.g., invariants are still met).
Note
After Python automatically finalizes an object, Python might start automatically clearing (
tp_clear
) the object and its referents (direct and indirect). Cleared objects are not guaranteed to be in a consistent state; a finalized object must be able to tolerate cleared referents.Note
An object is not guaranteed to be automatically finalized before its destructor (
tp_dealloc
) is called. It is recommended to callPyObject_CallFinalizerFromDealloc()
at the beginning oftp_dealloc
to guarantee that the object is always finalized before destruction.Note
The
tp_finalize
function can be called from any thread, although the GIL will be held.Note
The
tp_finalize
function can be called during shutdown, after some global variables have been deleted. See the documentation of the__del__()
method for details.When Python finalizes an object, it behaves like the following algorithm:
Python might mark the object as finalized. Currently, Python always marks objects whose type supports garbage collection (i.e., the
Py_TPFLAGS_HAVE_GC
flag is set intp_flags
) and never marks other types of objects; this might change in a future version.If the object is not marked as finalized and its
tp_finalize
finalizer function is non-NULL
, the finalizer function is called.If the finalizer function was called and the finalizer made the object reachable (i.e., there is a reference to the object and it is not a member of a cyclic isolate), then the finalizer is said to have resurrected the object. It is unspecified whether the finalizer can also resurrect the object by adding a new reference to the object that does not make it reachable, i.e., the object is (still) a member of a cyclic isolate.
If the finalizer resurrected the object, the object’s pending destruction is canceled and the object’s finalized mark might be removed if present. Currently, Python never removes the finalized mark; this might change in a future version.
Automatic finalization refers to any finalization performed by Python except via calls to
PyObject_CallFinalizer()
orPyObject_CallFinalizerFromDealloc()
. No guarantees are made about when, if, or how often an object is automatically finalized, except:Python will not automatically finalize an object if it is reachable, i.e., there is a reference to it and it is not a member of a cyclic isolate.
Python will not automatically finalize an object if finalizing it would not mark the object as finalized. Currently, this applies to objects whose type does not support garbage collection, i.e., the
Py_TPFLAGS_HAVE_GC
flag is not set. Such objects can still be manually finalized by callingPyObject_CallFinalizer()
orPyObject_CallFinalizerFromDealloc()
.Python will not automatically finalize any two members of a cyclic isolate concurrently.
Python will not automatically finalize an object after it has automatically cleared (
tp_clear
) the object.If an object is a member of a cyclic isolate, Python will not automatically finalize it after automatically clearing (see
tp_clear
) any other member.Python will automatically finalize every member of a cyclic isolate before it automatically clears (see
tp_clear
) any of them.If Python is going to automatically clear an object (
tp_clear
), it will automatically finalize the object first.
Python currently only automatically finalizes objects that are members of a cyclic isolate, but future versions might finalize objects regularly before their destruction.
To manually finalize an object, do not call this function directly; call
PyObject_CallFinalizer()
orPyObject_CallFinalizerFromDealloc()
instead.tp_finalize
should leave the current exception status unchanged. The recommended way to write a non-trivial finalizer is to back up the exception at the beginning by callingPyErr_GetRaisedException()
and restore the exception at the end by callingPyErr_SetRaisedException()
. If an exception is encountered in the middle of the finalizer, log and clear it withPyErr_WriteUnraisable()
orPyErr_FormatUnraisable()
. For example:static void foo_finalize(PyObject *self) { // Save the current exception, if any. PyObject *exc = PyErr_GetRaisedException(); // ... if (do_something_that_might_raise() != success_indicator) { PyErr_WriteUnraisable(self); goto done; } done: // Restore the saved exception. This silently discards any exception // raised above, so be sure to call PyErr_WriteUnraisable first if // necessary. PyErr_SetRaisedException(exc); }
Inheritance:
This field is inherited by subtypes.
Added in version 3.4.
Changed in version 3.8: Before version 3.8 it was necessary to set the
Py_TPFLAGS_HAVE_FINALIZE
flags bit in order for this field to be used. This is no longer required.See also
PEP 442: “Safe object finalization”
Object Life Cycle for details about how this slot relates to other slots.
-
vectorcallfunc PyTypeObject.tp_vectorcall¶
The corresponding slot ID
Py_tp_vectorcall
is part of the Stable ABI since version 3.14.A vectorcall function to use for calls of this type object (rather than instances). In other words,
tp_vectorcall
can be used to optimizetype.__call__
, which typically returns a new instance of type.As with any vectorcall function, if
tp_vectorcall
isNULL
, the tp_call protocol (Py_TYPE(type)->tp_call
) is used instead.Note
The vectorcall protocol requires that the vectorcall function has the same behavior as the corresponding
tp_call
. This means thattype->tp_vectorcall
must match the behavior ofPy_TYPE(type)->tp_call
.Specifically, if type uses the default metaclass,
type->tp_vectorcall
must behave the same as PyType_Type->tp_call, which:calls
type->tp_new
,if the result is a subclass of type, calls
type->tp_init
on the result oftp_new
, andreturns the result of
tp_new
.
Typically,
tp_vectorcall
is overridden to optimize this process for specifictp_new
andtp_init
. When doing this for user-subclassable types, note that both can be overridden (using__new__()
and__init__()
, respectively).Inheritance:
This field is never inherited.
Added in version 3.9: (the field exists since 3.8 but it’s only used since 3.9)
-
unsigned char PyTypeObject.tp_watched¶
Internal. Do not use.
Added in version 3.12.
Static Types¶
Traditionally, types defined in C code are static, that is,
a static PyTypeObject
structure is defined directly in code
and initialized using PyType_Ready()
.
This results in types that are limited relative to types defined in Python:
Static types are limited to one base, i.e. they cannot use multiple inheritance.
Static type objects (but not necessarily their instances) are immutable. It is not possible to add or modify the type object’s attributes from Python.
Static type objects are shared across sub-interpreters, so they should not include any subinterpreter-specific state.
Also, since PyTypeObject
is only part of the Limited API as an opaque struct, any extension modules using static types must be
compiled for a specific Python minor version.
Heap Types¶
An alternative to static types is heap-allocated types,
or heap types for short, which correspond closely to classes created by
Python’s class
statement. Heap types have the Py_TPFLAGS_HEAPTYPE
flag set.
This is done by filling a PyType_Spec
structure and calling
PyType_FromSpec()
, PyType_FromSpecWithBases()
,
PyType_FromModuleAndSpec()
, or PyType_FromMetaclass()
.
Number Object Structures¶
-
type PyNumberMethods¶
This structure holds pointers to the functions which an object uses to implement the number protocol. Each function is used by the function of similar name documented in the Number Protocol section.
Here is the structure definition:
typedef struct { binaryfunc nb_add; binaryfunc nb_subtract; binaryfunc nb_multiply; binaryfunc nb_remainder; binaryfunc nb_divmod; ternaryfunc nb_power; unaryfunc nb_negative; unaryfunc nb_positive; unaryfunc nb_absolute; inquiry nb_bool; unaryfunc nb_invert; binaryfunc nb_lshift; binaryfunc nb_rshift; binaryfunc nb_and; binaryfunc nb_xor; binaryfunc nb_or; unaryfunc nb_int; void *nb_reserved; unaryfunc nb_float; binaryfunc nb_inplace_add; binaryfunc nb_inplace_subtract; binaryfunc nb_inplace_multiply; binaryfunc nb_inplace_remainder; ternaryfunc nb_inplace_power; binaryfunc nb_inplace_lshift; binaryfunc nb_inplace_rshift; binaryfunc nb_inplace_and; binaryfunc nb_inplace_xor; binaryfunc nb_inplace_or; binaryfunc nb_floor_divide; binaryfunc nb_true_divide; binaryfunc nb_inplace_floor_divide; binaryfunc nb_inplace_true_divide; unaryfunc nb_index; binaryfunc nb_matrix_multiply; binaryfunc nb_inplace_matrix_multiply; } PyNumberMethods;
Note
Binary and ternary functions must check the type of all their operands, and implement the necessary conversions (at least one of the operands is an instance of the defined type). If the operation is not defined for the given operands, binary and ternary functions must return
Py_NotImplemented
, if another error occurred they must returnNULL
and set an exception.Note
The
nb_reserved
field should always beNULL
. It was previously callednb_long
, and was renamed in Python 3.0.1.
-
binaryfunc PyNumberMethods.nb_add¶
The corresponding slot ID
Py_nb_add
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_subtract¶
The corresponding slot ID
Py_nb_subtract
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_multiply¶
The corresponding slot ID
Py_nb_multiply
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_remainder¶
The corresponding slot ID
Py_nb_remainder
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_divmod¶
The corresponding slot ID
Py_nb_divmod
is part of the Stable ABI.
-
ternaryfunc PyNumberMethods.nb_power¶
The corresponding slot ID
Py_nb_power
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_negative¶
The corresponding slot ID
Py_nb_negative
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_positive¶
The corresponding slot ID
Py_nb_positive
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_absolute¶
The corresponding slot ID
Py_nb_absolute
is part of the Stable ABI.
-
inquiry PyNumberMethods.nb_bool¶
The corresponding slot ID
Py_nb_bool
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_invert¶
The corresponding slot ID
Py_nb_invert
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_lshift¶
The corresponding slot ID
Py_nb_lshift
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_rshift¶
The corresponding slot ID
Py_nb_rshift
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_and¶
The corresponding slot ID
Py_nb_and
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_xor¶
The corresponding slot ID
Py_nb_xor
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_or¶
The corresponding slot ID
Py_nb_or
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_int¶
The corresponding slot ID
Py_nb_int
is part of the Stable ABI.
-
void *PyNumberMethods.nb_reserved¶
-
unaryfunc PyNumberMethods.nb_float¶
The corresponding slot ID
Py_nb_float
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_add¶
The corresponding slot ID
Py_nb_inplace_add
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_subtract¶
The corresponding slot ID
Py_nb_inplace_subtract
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_multiply¶
The corresponding slot ID
Py_nb_inplace_multiply
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_remainder¶
The corresponding slot ID
Py_nb_inplace_remainder
is part of the Stable ABI.
-
ternaryfunc PyNumberMethods.nb_inplace_power¶
The corresponding slot ID
Py_nb_inplace_power
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_lshift¶
The corresponding slot ID
Py_nb_inplace_lshift
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_rshift¶
The corresponding slot ID
Py_nb_inplace_rshift
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_and¶
The corresponding slot ID
Py_nb_inplace_and
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_xor¶
The corresponding slot ID
Py_nb_inplace_xor
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_or¶
The corresponding slot ID
Py_nb_inplace_or
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_floor_divide¶
The corresponding slot ID
Py_nb_floor_divide
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_true_divide¶
The corresponding slot ID
Py_nb_true_divide
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_floor_divide¶
The corresponding slot ID
Py_nb_inplace_floor_divide
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_inplace_true_divide¶
The corresponding slot ID
Py_nb_inplace_true_divide
is part of the Stable ABI.
-
unaryfunc PyNumberMethods.nb_index¶
The corresponding slot ID
Py_nb_index
is part of the Stable ABI.
-
binaryfunc PyNumberMethods.nb_matrix_multiply¶
The corresponding slot ID
Py_nb_matrix_multiply
is part of the Stable ABI since version 3.5.
-
binaryfunc PyNumberMethods.nb_inplace_matrix_multiply¶
The corresponding slot ID
Py_nb_inplace_matrix_multiply
is part of the Stable ABI since version 3.5.
Mapping Object Structures¶
-
type PyMappingMethods¶
This structure holds pointers to the functions which an object uses to implement the mapping protocol. It has three members:
-
lenfunc PyMappingMethods.mp_length¶
The corresponding slot ID
Py_mp_length
is part of the Stable ABI.This function is used by
PyMapping_Size()
andPyObject_Size()
, and has the same signature. This slot may be set toNULL
if the object has no defined length.
-
binaryfunc PyMappingMethods.mp_subscript¶
The corresponding slot ID
Py_mp_subscript
is part of the Stable ABI.This function is used by
PyObject_GetItem()
andPySequence_GetSlice()
, and has the same signature asPyObject_GetItem()
. This slot must be filled for thePyMapping_Check()
function to return1
, it can beNULL
otherwise.
-
objobjargproc PyMappingMethods.mp_ass_subscript¶
The corresponding slot ID
Py_mp_ass_subscript
is part of the Stable ABI.This function is used by
PyObject_SetItem()
,PyObject_DelItem()
,PySequence_SetSlice()
andPySequence_DelSlice()
. It has the same signature asPyObject_SetItem()
, but v can also be set toNULL
to delete an item. If this slot isNULL
, the object does not support item assignment and deletion.
Sequence Object Structures¶
-
type PySequenceMethods¶
This structure holds pointers to the functions which an object uses to implement the sequence protocol.
-
lenfunc PySequenceMethods.sq_length¶
The corresponding slot ID
Py_sq_length
is part of the Stable ABI.This function is used by
PySequence_Size()
andPyObject_Size()
, and has the same signature. It is also used for handling negative indices via thesq_item
and thesq_ass_item
slots.
-
binaryfunc PySequenceMethods.sq_concat¶
The corresponding slot ID
Py_sq_concat
is part of the Stable ABI.This function is used by
PySequence_Concat()
and has the same signature. It is also used by the+
operator, after trying the numeric addition via thenb_add
slot.
-
ssizeargfunc PySequenceMethods.sq_repeat¶
The corresponding slot ID
Py_sq_repeat
is part of the Stable ABI.This function is used by
PySequence_Repeat()
and has the same signature. It is also used by the*
operator, after trying numeric multiplication via thenb_multiply
slot.
-
ssizeargfunc PySequenceMethods.sq_item¶
The corresponding slot ID
Py_sq_item
is part of the Stable ABI.This function is used by
PySequence_GetItem()
and has the same signature. It is also used byPyObject_GetItem()
, after trying the subscription via themp_subscript
slot. This slot must be filled for thePySequence_Check()
function to return1
, it can beNULL
otherwise.Negative indexes are handled as follows: if the
sq_length
slot is filled, it is called and the sequence length is used to compute a positive index which is passed tosq_item
. Ifsq_length
isNULL
, the index is passed as is to the function.
-
ssizeobjargproc PySequenceMethods.sq_ass_item¶
The corresponding slot ID
Py_sq_ass_item
is part of the Stable ABI.This function is used by
PySequence_SetItem()
and has the same signature. It is also used byPyObject_SetItem()
andPyObject_DelItem()
, after trying the item assignment and deletion via themp_ass_subscript
slot. This slot may be left toNULL
if the object does not support item assignment and deletion.
-
objobjproc PySequenceMethods.sq_contains¶
The corresponding slot ID
Py_sq_contains
is part of the Stable ABI.This function may be used by
PySequence_Contains()
and has the same signature. This slot may be left toNULL
, in this casePySequence_Contains()
simply traverses the sequence until it finds a match.
-
binaryfunc PySequenceMethods.sq_inplace_concat¶
The corresponding slot ID
Py_sq_inplace_concat
is part of the Stable ABI.This function is used by
PySequence_InPlaceConcat()
and has the same signature. It should modify its first operand, and return it. This slot may be left toNULL
, in this casePySequence_InPlaceConcat()
will fall back toPySequence_Concat()
. It is also used by the augmented assignment+=
, after trying numeric in-place addition via thenb_inplace_add
slot.
-
ssizeargfunc PySequenceMethods.sq_inplace_repeat¶
The corresponding slot ID
Py_sq_inplace_repeat
is part of the Stable ABI.This function is used by
PySequence_InPlaceRepeat()
and has the same signature. It should modify its first operand, and return it. This slot may be left toNULL
, in this casePySequence_InPlaceRepeat()
will fall back toPySequence_Repeat()
. It is also used by the augmented assignment*=
, after trying numeric in-place multiplication via thenb_inplace_multiply
slot.
Buffer Object Structures¶
-
type PyBufferProcs¶
This structure holds pointers to the functions required by the Buffer protocol. The protocol defines how an exporter object can expose its internal data to consumer objects.
-
getbufferproc PyBufferProcs.bf_getbuffer¶
The corresponding slot ID
Py_bf_getbuffer
is part of the Stable ABI since version 3.11.The signature of this function is:
int (PyObject *exporter, Py_buffer *view, int flags);
Handle a request to exporter to fill in view as specified by flags. Except for point (3), an implementation of this function MUST take these steps:
Check if the request can be met. If not, raise
BufferError
, set view->obj toNULL
and return-1
.Fill in the requested fields.
Increment an internal counter for the number of exports.
Set view->obj to exporter and increment view->obj.
Return
0
.
If exporter is part of a chain or tree of buffer providers, two main schemes can be used:
Re-export: Each member of the tree acts as the exporting object and sets view->obj to a new reference to itself.
Redirect: The buffer request is redirected to the root object of the tree. Here, view->obj will be a new reference to the root object.
The individual fields of view are described in section Buffer structure, the rules how an exporter must react to specific requests are in section Buffer request types.
All memory pointed to in the
Py_buffer
structure belongs to the exporter and must remain valid until there are no consumers left.format
,shape
,strides
,suboffsets
andinternal
are read-only for the consumer.PyBuffer_FillInfo()
provides an easy way of exposing a simple bytes buffer while dealing correctly with all request types.PyObject_GetBuffer()
is the interface for the consumer that wraps this function.
-
releasebufferproc PyBufferProcs.bf_releasebuffer¶
The corresponding slot ID
Py_bf_releasebuffer
is part of the Stable ABI since version 3.11.The signature of this function is:
void (PyObject *exporter, Py_buffer *view);
Handle a request to release the resources of the buffer. If no resources need to be released,
PyBufferProcs.bf_releasebuffer
may beNULL
. Otherwise, a standard implementation of this function will take these optional steps:Decrement an internal counter for the number of exports.
If the counter is
0
, free all memory associated with view.
The exporter MUST use the
internal
field to keep track of buffer-specific resources. This field is guaranteed to remain constant, while a consumer MAY pass a copy of the original buffer as the view argument.This function MUST NOT decrement view->obj, since that is done automatically in
PyBuffer_Release()
(this scheme is useful for breaking reference cycles).PyBuffer_Release()
is the interface for the consumer that wraps this function.
Async Object Structures¶
Added in version 3.5.
-
type PyAsyncMethods¶
This structure holds pointers to the functions required to implement awaitable and asynchronous iterator objects.
Here is the structure definition:
typedef struct { unaryfunc am_await; unaryfunc am_aiter; unaryfunc am_anext; sendfunc am_send; } PyAsyncMethods;
-
unaryfunc PyAsyncMethods.am_await¶
The corresponding slot ID
Py_am_await
is part of the Stable ABI since version 3.5.The signature of this function is:
PyObject *am_await(PyObject *self);
The returned object must be an iterator, i.e.
PyIter_Check()
must return1
for it.This slot may be set to
NULL
if an object is not an awaitable.
-
unaryfunc PyAsyncMethods.am_aiter¶
The corresponding slot ID
Py_am_aiter
is part of the Stable ABI since version 3.5.The signature of this function is:
PyObject *am_aiter(PyObject *self);
Must return an asynchronous iterator object. See
__anext__()
for details.This slot may be set to
NULL
if an object does not implement asynchronous iteration protocol.
-
unaryfunc PyAsyncMethods.am_anext¶
The corresponding slot ID
Py_am_anext
is part of the Stable ABI since version 3.5.The signature of this function is:
PyObject *am_anext(PyObject *self);
Must return an awaitable object. See
__anext__()
for details. This slot may be set toNULL
.
-
sendfunc PyAsyncMethods.am_send¶
The corresponding slot ID
Py_am_send
is part of the Stable ABI since version 3.10.The signature of this function is:
PySendResult am_send(PyObject *self, PyObject *arg, PyObject **result);
See
PyIter_Send()
for details. This slot may be set toNULL
.Added in version 3.10.
Slot Type typedefs¶
-
typedef PyObject *(*allocfunc)(PyTypeObject *cls, Py_ssize_t nitems)¶
- Part of the Stable ABI.
The purpose of this function is to separate memory allocation from memory initialization. It should return a pointer to a block of memory of adequate length for the instance, suitably aligned, and initialized to zeros, but with
ob_refcnt
set to1
andob_type
set to the type argument. If the type’stp_itemsize
is non-zero, the object’sob_size
field should be initialized to nitems and the length of the allocated memory block should betp_basicsize + nitems*tp_itemsize
, rounded up to a multiple ofsizeof(void*)
; otherwise, nitems is not used and the length of the block should betp_basicsize
.This function should not do any other instance initialization, not even to allocate additional memory; that should be done by
tp_new
.
-
typedef void (*destructor)(PyObject*)¶
- Part of the Stable ABI.
-
typedef PyObject *(*newfunc)(PyTypeObject*, PyObject*, PyObject*)¶
- Part of the Stable ABI.
See
tp_new
.
-
typedef PyObject *(*reprfunc)(PyObject*)¶
- Part of the Stable ABI.
See
tp_repr
.
-
typedef PyObject *(*getattrfunc)(PyObject *self, char *attr)¶
- Part of the Stable ABI.
Return the value of the named attribute for the object.
-
typedef int (*setattrfunc)(PyObject *self, char *attr, PyObject *value)¶
- Part of the Stable ABI.
Set the value of the named attribute for the object. The value argument is set to
NULL
to delete the attribute.
-
typedef PyObject *(*getattrofunc)(PyObject *self, PyObject *attr)¶
- Part of the Stable ABI.
Return the value of the named attribute for the object.
See
tp_getattro
.
-
typedef int (*setattrofunc)(PyObject *self, PyObject *attr, PyObject *value)¶
- Part of the Stable ABI.
Set the value of the named attribute for the object. The value argument is set to
NULL
to delete the attribute.See
tp_setattro
.
-
typedef PyObject *(*descrgetfunc)(PyObject*, PyObject*, PyObject*)¶
- Part of the Stable ABI.
See
tp_descr_get
.
-
typedef int (*descrsetfunc)(PyObject*, PyObject*, PyObject*)¶
- Part of the Stable ABI.
See
tp_descr_set
.
-
typedef Py_hash_t (*hashfunc)(PyObject*)¶
- Part of the Stable ABI.
See
tp_hash
.
-
typedef PyObject *(*richcmpfunc)(PyObject*, PyObject*, int)¶
- Part of the Stable ABI.
See
tp_richcompare
.
-
typedef PyObject *(*getiterfunc)(PyObject*)¶
- Part of the Stable ABI.
See
tp_iter
.
-
typedef PyObject *(*iternextfunc)(PyObject*)¶
- Part of the Stable ABI.
See
tp_iternext
.
-
typedef Py_ssize_t (*lenfunc)(PyObject*)¶
- Part of the Stable ABI.
-
typedef int (*getbufferproc)(PyObject*, Py_buffer*, int)¶
- Part of the Stable ABI since version 3.12.
-
typedef void (*releasebufferproc)(PyObject*, Py_buffer*)¶
- Part of the Stable ABI since version 3.12.
-
typedef PyObject *(*unaryfunc)(PyObject*)¶
- Part of the Stable ABI.
-
typedef PyObject *(*binaryfunc)(PyObject*, PyObject*)¶
- Part of the Stable ABI.
-
typedef PyObject *(*ssizeargfunc)(PyObject*, Py_ssize_t)¶
- Part of the Stable ABI.
-
typedef int (*ssizeobjargproc)(PyObject*, Py_ssize_t, PyObject*)¶
- Part of the Stable ABI.
-
typedef int (*objobjproc)(PyObject*, PyObject*)¶
- Part of the Stable ABI.
-
typedef int (*objobjargproc)(PyObject*, PyObject*, PyObject*)¶
- Part of the Stable ABI.
Examples¶
The following are simple examples of Python type definitions. They include common usage you may encounter. Some demonstrate tricky corner cases. For more examples, practical info, and a tutorial, see Defining Extension Types: Tutorial and Defining Extension Types: Assorted Topics.
A basic static type:
typedef struct {
PyObject_HEAD
const char *data;
} MyObject;
static PyTypeObject MyObject_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "mymod.MyObject",
.tp_basicsize = sizeof(MyObject),
.tp_doc = PyDoc_STR("My objects"),
.tp_new = myobj_new,
.tp_dealloc = (destructor)myobj_dealloc,
.tp_repr = (reprfunc)myobj_repr,
};
You may also find older code (especially in the CPython code base) with a more verbose initializer:
static PyTypeObject MyObject_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
"mymod.MyObject", /* tp_name */
sizeof(MyObject), /* tp_basicsize */
0, /* tp_itemsize */
(destructor)myobj_dealloc, /* tp_dealloc */
0, /* tp_vectorcall_offset */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_as_async */
(reprfunc)myobj_repr, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
0, /* tp_flags */
PyDoc_STR("My objects"), /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
0, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
myobj_new, /* tp_new */
};
A type that supports weakrefs, instance dicts, and hashing:
typedef struct {
PyObject_HEAD
const char *data;
} MyObject;
static PyTypeObject MyObject_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "mymod.MyObject",
.tp_basicsize = sizeof(MyObject),
.tp_doc = PyDoc_STR("My objects"),
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_MANAGED_DICT |
Py_TPFLAGS_MANAGED_WEAKREF,
.tp_new = myobj_new,
.tp_traverse = (traverseproc)myobj_traverse,
.tp_clear = (inquiry)myobj_clear,
.tp_alloc = PyType_GenericNew,
.tp_dealloc = (destructor)myobj_dealloc,
.tp_repr = (reprfunc)myobj_repr,
.tp_hash = (hashfunc)myobj_hash,
.tp_richcompare = PyBaseObject_Type.tp_richcompare,
};
A str subclass that cannot be subclassed and cannot be called
to create instances (e.g. uses a separate factory func) using
Py_TPFLAGS_DISALLOW_INSTANTIATION
flag:
typedef struct {
PyUnicodeObject raw;
char *extra;
} MyStr;
static PyTypeObject MyStr_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "mymod.MyStr",
.tp_basicsize = sizeof(MyStr),
.tp_base = NULL, // set to &PyUnicode_Type in module init
.tp_doc = PyDoc_STR("my custom str"),
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
.tp_repr = (reprfunc)myobj_repr,
};
The simplest static type with fixed-length instances:
typedef struct {
PyObject_HEAD
} MyObject;
static PyTypeObject MyObject_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "mymod.MyObject",
};
The simplest static type with variable-length instances:
typedef struct {
PyObject_VAR_HEAD
const char *data[1];
} MyObject;
static PyTypeObject MyObject_Type = {
PyVarObject_HEAD_INIT(NULL, 0)
.tp_name = "mymod.MyObject",
.tp_basicsize = sizeof(MyObject) - sizeof(char *),
.tp_itemsize = sizeof(char *),
};