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 typedef-examples section provides at-a-glance insight into the meaning and use of PyTypeObject.

Quick Reference

"tp slots"

PyTypeObject Slot1	Type <slot-typedefs-table>	special methods/attrs	Info2
			O	T	D	I
<R> ~PyTypeObject.tp_name	const char *	__name__	X	X
~PyTypeObject.tp_basicsize	Py_ssize_t		X	X		X
~PyTypeObject.tp_itemsize	Py_ssize_t			X		X
~PyTypeObject.tp_dealloc	destructor		X	X		X
~PyTypeObject.tp_vectorcall_offset	Py_ssize_t			X		X
(~PyTypeObject.tp_getattr)	getattrfunc	__getattribute__, __getattr__				G
(~PyTypeObject.tp_setattr)	setattrfunc	__setattr__, __delattr__				G
~PyTypeObject.tp_as_async	PyAsyncMethods *	sub-slots				%
~PyTypeObject.tp_repr	reprfunc	__repr__	X	X		X
~PyTypeObject.tp_as_number	PyNumberMethods *	sub-slots				%
~PyTypeObject.tp_as_sequence	PySequenceMethods *	sub-slots				%
~PyTypeObject.tp_as_mapping	PyMappingMethods *	sub-slots				%
~PyTypeObject.tp_hash	hashfunc	__hash__	X			G
~PyTypeObject.tp_call	ternaryfunc	__call__		X		X
~PyTypeObject.tp_str	reprfunc	__str__	X			X
~PyTypeObject.tp_getattro	getattrofunc	__getattribute__, __getattr__	X	X		G
~PyTypeObject.tp_setattro	setattrofunc	__setattr__, __delattr__	X	X		G
~PyTypeObject.tp_as_buffer	PyBufferProcs *	sub-slots				%
~PyTypeObject.tp_flags	unsigned long		X	X		?
~PyTypeObject.tp_doc	const char *	__doc__	X	X
~PyTypeObject.tp_traverse	traverseproc			X		G
~PyTypeObject.tp_clear	inquiry			X		G
~PyTypeObject.tp_richcompare	richcmpfunc	__lt__, __le__, __eq__, __ne__, __gt__, __ge__	X			G
(~PyTypeObject.tp_weaklistoffset)	Py_ssize_t			X		?
~PyTypeObject.tp_iter	getiterfunc	__iter__				X
~PyTypeObject.tp_iternext	iternextfunc	__next__				X
~PyTypeObject.tp_methods	PyMethodDef []		X	X
~PyTypeObject.tp_members	PyMemberDef []			X
~PyTypeObject.tp_getset	PyGetSetDef []		X	X
~PyTypeObject.tp_base	PyTypeObject *	__base__			X
~PyTypeObject.tp_dict	PyObject *	__dict__			?
~PyTypeObject.tp_descr_get	descrgetfunc	__get__				X
~PyTypeObject.tp_descr_set	descrsetfunc	__set__, __delete__				X
(~PyTypeObject.tp_dictoffset)	Py_ssize_t			X		?
~PyTypeObject.tp_init	initproc	__init__	X	X		X
~PyTypeObject.tp_alloc	allocfunc		X		?	?
~PyTypeObject.tp_new	newfunc	__new__	X	X	?	?
~PyTypeObject.tp_free	freefunc		X	X	?	?
~PyTypeObject.tp_is_gc	inquiry			X		X
<~PyTypeObject.tp_bases>	PyObject *	__bases__			~
<~PyTypeObject.tp_mro>	PyObject *	__mro__			~
[~PyTypeObject.tp_cache]	PyObject *
[~PyTypeObject.tp_subclasses]	void *	__subclasses__
[~PyTypeObject.tp_weaklist]	PyObject *
(~PyTypeObject.tp_del)	destructor
[~PyTypeObject.tp_version_tag]	unsigned int
~PyTypeObject.tp_finalize	destructor	__del__				X
~PyTypeObject.tp_vectorcall	vectorcallfunc
[~PyTypeObject.tp_watched]	unsigned char

---

1. (): A slot name in parentheses indicates it is (effectively) deprecated.

   <>: Names in angle brackets should be initially set to NULL and treated as read-only.

   []: Names in square brackets are for internal use only.

   <R> (as a prefix) means the field is required (must be non-NULL).↩︎

2. Columns:

   "O": set on PyBaseObject_Type

   "T": set on PyType_Type

   "D": default (if slot is set to NULL)

   X - PyType_Ready sets this value if it is NULL
   ~ - PyType_Ready always sets this value (it should be NULL)
   ? - PyType_Ready may set this value depending on other slots
   
   Also see the inheritance column ("I").

   "I": inheritance

   X - type slot is inherited via *PyType_Ready* if defined with a *NULL* value
   % - the slots of the sub-struct are inherited individually
   G - inherited, but only in combination with other slots; see the slot's description
   ? - it's complicated; see the slot's description

   Note that some slots are effectively inherited through the normal attribute lookup chain.↩︎

sub-slots

Slot	Type <slot-typedefs-table>	special methods
~PyAsyncMethods.am_await	unaryfunc	__await__
~PyAsyncMethods.am_aiter	unaryfunc	__aiter__
~PyAsyncMethods.am_anext	unaryfunc	__anext__
~PyAsyncMethods.am_send	sendfunc
~PyNumberMethods.nb_add	binaryfunc	__add__ __radd__
~PyNumberMethods.nb_inplace_add	binaryfunc	__iadd__
~PyNumberMethods.nb_subtract	binaryfunc	__sub__ __rsub__
~PyNumberMethods.nb_inplace_subtract	binaryfunc	__isub__
~PyNumberMethods.nb_multiply	binaryfunc	__mul__ __rmul__
~PyNumberMethods.nb_inplace_multiply	binaryfunc	__imul__
~PyNumberMethods.nb_remainder	binaryfunc	__mod__ __rmod__
~PyNumberMethods.nb_inplace_remainder	binaryfunc	__imod__
~PyNumberMethods.nb_divmod	binaryfunc	__divmod__ __rdivmod__
~PyNumberMethods.nb_power	ternaryfunc	__pow__ __rpow__
~PyNumberMethods.nb_inplace_power	ternaryfunc	__ipow__
~PyNumberMethods.nb_negative	unaryfunc	__neg__
~PyNumberMethods.nb_positive	unaryfunc	__pos__
~PyNumberMethods.nb_absolute	unaryfunc	__abs__
~PyNumberMethods.nb_bool	inquiry	__bool__
~PyNumberMethods.nb_invert	unaryfunc	__invert__
~PyNumberMethods.nb_lshift	binaryfunc	__lshift__ __rlshift__
~PyNumberMethods.nb_inplace_lshift	binaryfunc	__ilshift__
~PyNumberMethods.nb_rshift	binaryfunc	__rshift__ __rrshift__
~PyNumberMethods.nb_inplace_rshift	binaryfunc	__irshift__
~PyNumberMethods.nb_and	binaryfunc	__and__ __rand__
~PyNumberMethods.nb_inplace_and	binaryfunc	__iand__
~PyNumberMethods.nb_xor	binaryfunc	__xor__ __rxor__
~PyNumberMethods.nb_inplace_xor	binaryfunc	__ixor__
~PyNumberMethods.nb_or	binaryfunc	__or__ __ror__
~PyNumberMethods.nb_inplace_or	binaryfunc	__ior__
~PyNumberMethods.nb_int	unaryfunc	__int__
~PyNumberMethods.nb_reserved	void *
~PyNumberMethods.nb_float	unaryfunc	__float__
~PyNumberMethods.nb_floor_divide	binaryfunc	__floordiv__
~PyNumberMethods.nb_inplace_floor_divide	binaryfunc	__ifloordiv__
~PyNumberMethods.nb_true_divide	binaryfunc	__truediv__
~PyNumberMethods.nb_inplace_true_divide	binaryfunc	__itruediv__
~PyNumberMethods.nb_index	unaryfunc	__index__
~PyNumberMethods.nb_matrix_multiply	binaryfunc	__matmul__ __rmatmul__
~PyNumberMethods.nb_inplace_matrix_multiply	binaryfunc	__imatmul__
~PyMappingMethods.mp_length	lenfunc	__len__
~PyMappingMethods.mp_subscript	binaryfunc	__getitem__
~PyMappingMethods.mp_ass_subscript	objobjargproc	__setitem__, __delitem__
~PySequenceMethods.sq_length	lenfunc	__len__
~PySequenceMethods.sq_concat	binaryfunc	__add__
~PySequenceMethods.sq_repeat	ssizeargfunc	__mul__
~PySequenceMethods.sq_item	ssizeargfunc	__getitem__
~PySequenceMethods.sq_ass_item	ssizeobjargproc	__setitem__ __delitem__
~PySequenceMethods.sq_contains	objobjproc	__contains__
~PySequenceMethods.sq_inplace_concat	binaryfunc	__iadd__
~PySequenceMethods.sq_inplace_repeat	ssizeargfunc	__imul__
~PyBufferProcs.bf_getbuffer	getbufferproc	__buffer__
~PyBufferProcs.bf_releasebuffer	releasebufferproc	__release_buffer__

slot typedefs

typedef	Parameter Types	Return Type
allocfunc	PyTypeObject * Py_ssize_t	PyObject *
destructor	PyObject *	void
freefunc	void *	void
traverseproc	PyObject * visitproc void *	int
newfunc	PyTypeObject * PyObject * PyObject *	PyObject *
initproc	PyObject * PyObject * PyObject *	int
reprfunc	PyObject *	PyObject *
getattrfunc	PyObject * const char *	PyObject *
setattrfunc	PyObject * const char * PyObject *	int
getattrofunc	PyObject * PyObject *	PyObject *
setattrofunc	PyObject * PyObject * PyObject *	int
descrgetfunc	PyObject * PyObject * PyObject *	PyObject *
descrsetfunc	PyObject * PyObject * PyObject *	int
hashfunc	PyObject *	Py_hash_t
richcmpfunc	PyObject * PyObject * int	PyObject *
getiterfunc	PyObject *	PyObject *
iternextfunc	PyObject *	PyObject *
lenfunc	PyObject *	Py_ssize_t
getbufferproc	PyObject * Py_buffer * int	int
releasebufferproc	PyObject * Py_buffer *	void
inquiry	PyObject *	int
unaryfunc	PyObject *	PyObject *
binaryfunc	PyObject * PyObject *	PyObject *
ternaryfunc	PyObject * PyObject * PyObject *	PyObject *
ssizeargfunc	PyObject * Py_ssize_t	PyObject *
ssizeobjargproc	PyObject * Py_ssize_t PyObject *	int
objobjproc	PyObject * PyObject *	int
objobjargproc	PyObject * PyObject * PyObject *	int

See slot-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:

PyObject Slots

The type object structure extends the PyVarObject structure. The ~PyVarObject.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 ~PyTypeObject.tp_itemsize, which means that its instances (i.e. type objects) must have the ~PyVarObject.ob_size field.

PyObject.ob_refcnt

The type object's reference count is initialized to 1 by the PyObject_HEAD_INIT macro. Note that for statically allocated type objects <static-types>, the type's instances (objects whose ~PyObject.ob_type points back to the type) do not count as references. But for dynamically allocated type objects <heap-types>, the instances do count as references.

Inheritance:

This field is not inherited by subtypes.

PyObject.ob_type

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 pass NULL to the PyObject_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 if ~PyObject.ob_type is NULL, and if so, initializes it to the ~PyObject.ob_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

PyVarObject.ob_size

For statically allocated type objects <static-types>, this should be initialized to zero. For dynamically allocated type objects <heap-types>, 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.)

See Py_tp_name for the corresponding Slot ID <PySlot.sl_id>.

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 module !M in subpackage !Q in package !P should have the ~PyTypeObject.tp_name initializer "P.Q.M.T".

For dynamically allocated type objects <heap-types>, 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 <static-types>, the tp_name field should contain a dot. Everything before the last dot is made accessible as the ~type.__module__ attribute, and everything after the last dot is made accessible as the ~type.__name__ attribute.

If no dot is present, the entire ~PyTypeObject.tp_name field is made accessible as the ~type.__name__ attribute, and the ~type.__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 in PyTypeObject (other than potentially ~PyTypeObject.tp_itemsize).

Inheritance:

This field is not inherited by subtypes.

Py_tp_dealloc

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's ~PyTypeObject.tp_free function to free the object itself.

If you may call functions that may set the error indicator, you must use PyErr_GetRaisedException and PyErr_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 (~PyTypeObject.tp_finalize) subsequently resurrects the object.
• An object will not be destroyed while it is being automatically finalized (~PyTypeObject.tp_finalize) or automatically cleared (~PyTypeObject.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 of !tp_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 call PyObject_GC_UnTrack before clearing any member fields.

It is permissible to call ~PyTypeObject.tp_clear from !tp_dealloc to reduce code duplication and to guarantee that the object is always cleared before destruction. Beware that !tp_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 (via Py_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 with PyErr_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 which !tp_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 called !tp_dealloc will not violate any assumptions of the library.

Inheritance:

This field is inherited by subtypes.

life-cycle for details about how this slot relates to other slots.

An optional offset to a per-instance function that implements calling the object using the vectorcall protocol <vectorcall>, a more efficient alternative of the simpler ~PyTypeObject.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 a vectorcallfunc pointer.

The vectorcallfunc pointer may be NULL, in which case the instance behaves as if Py_TPFLAGS_HAVE_VECTORCALL was not set: calling the instance falls back to ~PyTypeObject.tp_call.

Any class that sets Py_TPFLAGS_HAVE_VECTORCALL must also set ~PyTypeObject.tp_call and make sure its behaviour is consistent with the vectorcallfunc function. This can be done by setting tp_call to PyVectorcall_Call.

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.

3.12

Before version 3.12, it was not recommended for mutable heap types <heap-types> to implement the vectorcall protocol. When a user sets ~object.__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 the Py_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 <vectorcall>, except when PyVectorcall_Call is explicitly called.

Py_tp_getattr

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 ~PyTypeObject.tp_getattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: ~PyTypeObject.tp_getattr, ~PyTypeObject.tp_getattro

This field is inherited by subtypes together with ~PyTypeObject.tp_getattro: a subtype inherits both ~PyTypeObject.tp_getattr and ~PyTypeObject.tp_getattro from its base type when the subtype's ~PyTypeObject.tp_getattr and ~PyTypeObject.tp_getattro are both NULL.

Py_tp_setattr

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 ~PyTypeObject.tp_setattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: ~PyTypeObject.tp_setattr, ~PyTypeObject.tp_setattro

This field is inherited by subtypes together with ~PyTypeObject.tp_setattro: a subtype inherits both ~PyTypeObject.tp_setattr and ~PyTypeObject.tp_setattro from its base type when the subtype's ~PyTypeObject.tp_setattr and ~PyTypeObject.tp_setattro are both NULL.

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-structs for details.

3.5 Formerly known as tp_compare and tp_reserved.

Inheritance:

The ~PyTypeObject.tp_as_async field is not inherited, but the contained fields are inherited individually.

Py_tp_repr

pair: built-in function; repr

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.

Pointer to an additional structure that contains fields relevant only to objects which implement the number protocol. These fields are documented in number-structs.

Inheritance:

The ~PyTypeObject.tp_as_number field is not inherited, but the contained fields are inherited individually.

Pointer to an additional structure that contains fields relevant only to objects which implement the sequence protocol. These fields are documented in sequence-structs.

Inheritance:

The ~PyTypeObject.tp_as_sequence field is not inherited, but the contained fields are inherited individually.

Pointer to an additional structure that contains fields relevant only to objects which implement the mapping protocol. These fields are documented in mapping-structs.

Inheritance:

The ~PyTypeObject.tp_as_mapping field is not inherited, but the contained fields are inherited individually.

Py_tp_hash

pair: built-in function; hash

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 ~PyTypeObject.tp_richcompare is not set), an attempt to take the hash of the object raises TypeError. This is the same as setting it to PyObject_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, causing isinstance(o, collections.Hashable) to correctly return False. Note that the converse is also true - setting __hash__ = None on a class at the Python level will result in the tp_hash slot being set to PyObject_HashNotImplemented.

Inheritance:

Group: ~PyTypeObject.tp_hash, ~PyTypeObject.tp_richcompare

This field is inherited by subtypes together with ~PyTypeObject.tp_richcompare: a subtype inherits both of ~PyTypeObject.tp_richcompare and ~PyTypeObject.tp_hash, when the subtype's ~PyTypeObject.tp_richcompare and ~PyTypeObject.tp_hash are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericHash.

Py_tp_call

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 for PyObject_Call:

PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);

Inheritance:

This field is inherited by subtypes.

Py_tp_str

An optional pointer to a function that implements the built-in operation str. (Note that str is a type now, and str calls the constructor for that type. This constructor calls PyObject_Str to do the actual work, and PyObject_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.

Py_tp_getattro

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: ~PyTypeObject.tp_getattr, ~PyTypeObject.tp_getattro

This field is inherited by subtypes together with ~PyTypeObject.tp_getattr: a subtype inherits both ~PyTypeObject.tp_getattr and ~PyTypeObject.tp_getattro from its base type when the subtype's ~PyTypeObject.tp_getattr and ~PyTypeObject.tp_getattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericGetAttr.

Py_tp_setattro

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 to PyObject_GenericSetAttr, which implements the normal way of setting object attributes.

Inheritance:

Group: ~PyTypeObject.tp_setattr, ~PyTypeObject.tp_setattro

This field is inherited by subtypes together with ~PyTypeObject.tp_setattr: a subtype inherits both ~PyTypeObject.tp_setattr and ~PyTypeObject.tp_setattro from its base type when the subtype's ~PyTypeObject.tp_setattr and ~PyTypeObject.tp_setattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericSetAttr.

Pointer to an additional structure that contains fields relevant only to objects which implement the buffer interface. These fields are documented in buffer-structs.

Inheritance:

The ~PyTypeObject.tp_as_buffer field is not inherited, but the contained fields are inherited individually.

See Py_tp_flags for the corresponding Slot ID <PySlot.sl_id>.

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 ~PyTypeObject.tp_as_number, ~PyTypeObject.tp_as_sequence, ~PyTypeObject.tp_as_mapping, and ~PyTypeObject.tp_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 or NULL 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 the ~PyTypeObject.tp_traverse and ~PyTypeObject.tp_clear fields, i.e. if the Py_TPFLAGS_HAVE_GC flag bit is clear in the subtype and the ~PyTypeObject.tp_traverse and ~PyTypeObject.tp_clear fields in the subtype exist and have NULL values.

Default:

PyBaseObject_Type uses Py_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 the ~PyTypeObject.tp_flags field. The macro PyType_HasFeature takes a type and a flags value, tp and f, and checks whether tp->tp_flags & f is non-zero.

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, the ~PyObject.ob_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 <supporting-cycle-detection> as they can form a reference cycle with their own module object.

Inheritance:

???

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:

???

This bit is set when the type object has been fully initialized by PyType_Ready.

Inheritance:

???

This bit is set while PyType_Ready is in the process of initializing the type object.

Inheritance:

???

This bit is set when the object supports garbage collection. If this bit is set, memory for new instances (see ~PyTypeObject.tp_alloc) must be allocated using PyObject_GC_New or PyType_GenericAlloc and deallocated (see ~PyTypeObject.tp_free) using PyObject_GC_Del. More information in section supporting-cycle-detection.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, ~PyTypeObject.tp_traverse, ~PyTypeObject.tp_clear

The Py_TPFLAGS_HAVE_GC flag bit is inherited together with the ~PyTypeObject.tp_traverse and ~PyTypeObject.tp_clear fields, i.e. if the Py_TPFLAGS_HAVE_GC flag bit is clear in the subtype and the ~PyTypeObject.tp_traverse and ~PyTypeObject.tp_clear fields in the subtype exist and have NULL values.

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:

???

This bit indicates that objects behave like unbound methods.

If this flag is set for type(meth), then:

• meth.__get__(obj, cls)(*args, **kwds) (with obj not None) must be equivalent to meth(obj, *args, **kwds).
• meth.__get__(None, cls)(*args, **kwds) must be equivalent to meth(*args, **kwds).

This flag enables an optimization for typical method calls like obj.meth(): it avoids creating a temporary "bound method" object for obj.meth.

3.8

Inheritance:

This flag is never inherited by types without the Py_TPFLAGS_IMMUTABLETYPE flag set. For extension types, it is inherited whenever ~PyTypeObject.tp_descr_get is inherited.

This bit indicates that instances of the class have a ~object.__dict__ attribute, and that the space for the dictionary is managed by the VM.

If this flag is set, Py_TPFLAGS_HAVE_GC must also be set.

The type traverse function must call PyObject_VisitManagedDict and its clear function must call PyObject_ClearManagedDict.

3.12

Inheritance:

This flag is inherited unless the ~PyTypeObject.tp_dictoffset field is set in a superclass.

This bit indicates that instances of the class should be weakly referenceable.

If this flag is set, Py_TPFLAGS_HAVE_GC must also be set.

3.12

Inheritance:

This flag is inherited unless the ~PyTypeObject.tp_weaklistoffset field is set in a superclass.

These bits indicate that the VM will manage some fields by storing them before the object. Currently, this macro is equivalent to Py_TPFLAGS_MANAGED_DICT | Py_TPFLAGS_MANAGED_WEAKREF.

This macro value relies on the implementation of the VM, so its value is not stable and may change in a future version. Prefer using individual flags instead.

3.12

Only usable with variable-size types, i.e. ones with non-zero ~PyTypeObject.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.

3.12

Inheritance:

This flag is inherited.

Functions such as PyLong_Check will call PyType_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, like PyObject_IsInstance. Custom types that inherit from built-ins should have their ~PyTypeObject.tp_flags set appropriately, or the code that interacts with such types will behave differently depending on what kind of check is used.

This bit is set when the ~PyTypeObject.tp_finalize slot is present in the type structure.

3.4

3.8 This flag isn't necessary anymore, as the interpreter assumes the ~PyTypeObject.tp_finalize slot is always present in the type structure.

This bit is set when the class implements the vectorcall protocol <vectorcall>. See ~PyTypeObject.tp_vectorcall_offset for details.

Inheritance:

This bit is inherited if ~PyTypeObject.tp_call is also inherited.

3.8 as _Py_TPFLAGS_HAVE_VECTORCALL

3.9

Renamed to the current name, without the leading underscore. The old provisional name is soft deprecated.

3.12

This flag is now removed from a class when the class's ~object.__call__ method is reassigned.

This flag can now be inherited by mutable classes.

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 <static-types>.

Inheritance:

This flag is not inherited.

3.10

Disallow creating instances of the type: set ~PyTypeObject.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 <static-types> if ~PyTypeObject.tp_base is NULL or &PyBaseObject_Type and ~PyTypeObject.tp_new is NULL.

Inheritance:

This flag is not inherited. However, subclasses will not be instantiable unless they provide a non-NULL ~PyTypeObject.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 ~PyTypeObject.tp_new only succeed for subclasses.

3.10

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 subclassing collections.abc.Mapping, and unset when registering collections.abc.Sequence.

[!NOTE] Py_TPFLAGS_MAPPING and Py_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.

634 -- Structural Pattern Matching: Specification

3.10

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 subclassing collections.abc.Sequence, and unset when registering collections.abc.Mapping.

[!NOTE] Py_TPFLAGS_MAPPING and Py_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.

634 -- Structural Pattern Matching: Specification

3.10

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

This macro does nothing. Historically, this would indicate that the ~PyTypeObject.tp_version_tag field was available and initialized.

3.13

This bit indicates that instances of this type will have an "inline values" array (containing the object's attributes) placed directly after the end of the object.

This requires that Py_TPFLAGS_HAVE_GC is set.

Inheritance:

This flag is not inherited.

3.13

This bit indicates that this is an abstract type and therefore cannot be instantiated.

Inheritance:

This flag is not inherited.

abc

Internal. Do not set or unset this flag. Historically, this was a reserved flag for use in Stackless Python.

[!WARNING] This flag is present in header files, but is not be used. This may be removed in a future version of CPython.

Py_tp_doc

An optional pointer to a NUL-terminated C string giving the docstring for this type object. This is exposed as the ~type.__doc__ attribute on the type and instances of the type.

Inheritance:

This field is not inherited by subtypes.

Py_tp_traverse

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.

See gc-traversal for documentation.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, ~PyTypeObject.tp_traverse, ~PyTypeObject.tp_clear

This field is inherited by subtypes together with ~PyTypeObject.tp_clear and the Py_TPFLAGS_HAVE_GC flag bit: the flag bit, ~PyTypeObject.tp_traverse, and ~PyTypeObject.tp_clear are all inherited from the base type if they are all zero in the subtype.

Py_tp_clear

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's ~PyTypeObject.tp_dealloc function to invoke !tp_clear to avoid code duplication. (Beware that !tp_clear might have already been called. Prefer calling idempotent functions like Py_CLEAR.)

Any non-trivial cleanup should be performed in ~PyTypeObject.tp_finalize instead of !tp_clear.

[!NOTE] If !tp_clear fails to break a reference cycle then the objects in the cyclic isolate may remain indefinitely uncollectable ("leak"). See gc.garbage.

[!NOTE] Referents (direct and indirect) might have already been cleared; they are not guaranteed to be in a consistent state.

[!NOTE] The ~PyTypeObject.tp_clear function can be called from any thread.

[!NOTE] An object is not guaranteed to be automatically cleared before its destructor (~PyTypeObject.tp_dealloc) is called.

This function differs from the destructor (~PyTypeObject.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 ~PyTypeObject.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 (~PyTypeObject.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 ~PyTypeObject.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 (~PyTypeObject.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 the self pointer while !tp_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 ~PyTypeObject.tp_clear functions in the system must combine to break all reference cycles. This is subtle, and if in any doubt supply a ~PyTypeObject.tp_clear function. For example, the tuple type does not implement a ~PyTypeObject.tp_clear function, because it's possible to prove that no reference cycle can be composed entirely of tuples. Therefore the ~PyTypeObject.tp_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 implementing ~PyTypeObject.tp_clear.

Implementations of ~PyTypeObject.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 to NULL, 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 (via Py_DECREF) until after the pointer to the contained object is set to NULL. 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 be NULL at that time, so that self knows the contained object can no longer be used. The Py_CLEAR macro performs the operations in a safe order.

If the Py_TPFLAGS_MANAGED_DICT bit is set in the ~PyTypeObject.tp_flags field, the clear function must call PyObject_ClearManagedDict like this:

PyObject_ClearManagedDict((PyObject*)self);

More information about Python's garbage collection scheme can be found in section supporting-cycle-detection.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, ~PyTypeObject.tp_traverse, ~PyTypeObject.tp_clear

This field is inherited by subtypes together with ~PyTypeObject.tp_traverse and the Py_TPFLAGS_HAVE_GC flag bit: the flag bit, ~PyTypeObject.tp_traverse, and ~PyTypeObject.tp_clear are all inherited from the base type if they are all zero in the subtype.

life-cycle for details about how this slot relates to other slots.

Py_tp_richcompare

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 or Py_False). If the comparison is undefined, it must return Py_NotImplemented, if another error occurred it must return NULL and set an exception condition.

The following constants are defined to be used as the third argument for ~PyTypeObject.tp_richcompare and for PyObject_RichCompare:

Constant	Comparison
	<
	<=
	==
	!=
	>
	>=

The following macro is defined to ease writing rich comparison functions:

Return Py_True or Py_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 for PyObject_RichCompare.

The returned value is a new strong reference.

On error, sets an exception and returns NULL from the function.

3.7

Inheritance:

Group: ~PyTypeObject.tp_hash, ~PyTypeObject.tp_richcompare

This field is inherited by subtypes together with ~PyTypeObject.tp_hash: a subtype inherits ~PyTypeObject.tp_richcompare and ~PyTypeObject.tp_hash when the subtype's ~PyTypeObject.tp_richcompare and ~PyTypeObject.tp_hash are both NULL.

Default:

PyBaseObject_Type provides a ~PyTypeObject.tp_richcompare implementation, which may be inherited. However, if only ~PyTypeObject.tp_hash is defined, not even the inherited function is used and instances of the type will not be able to participate in any comparisons.

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 the PyWeakref_* functions. The instance structure needs to include a field of type PyObject* which is initialized to NULL.

Do not confuse this field with ~PyTypeObject.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 and ~PyTypeObject.tp_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 ~PyTypeObject.tp_weaklistoffset, this should not be a problem.

Default:

If the Py_TPFLAGS_MANAGED_WEAKREF bit is set in the ~PyTypeObject.tp_flags field, then ~PyTypeObject.tp_weaklistoffset will be set to a negative value, to indicate that it is unsafe to use this field.

Py_tp_iter

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.

Py_tp_iternext

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, the tp_iternext function must return NULL; a StopIteration exception may or may not be set. When another error occurs, it must return NULL too. The presence of tp_iternext signals that the instances of this type are iterators.

Iterator types should also define the ~PyTypeObject.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.

Py_tp_methods

An optional pointer to a static NULL-terminated array of PyMethodDef structures, declaring regular methods of this type.

For each entry in the array, an entry is added to the type's dictionary (see ~PyTypeObject.tp_dict below) containing a method descriptor.

Inheritance:

This field is not inherited by subtypes (methods are inherited through a different mechanism).

Py_tp_members

An optional pointer to a static NULL-terminated array of PyMemberDef 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 ~PyTypeObject.tp_dict below) containing a member descriptor.

Inheritance:

This field is not inherited by subtypes (members are inherited through a different mechanism).

Py_tp_getset

An optional pointer to a static NULL-terminated array of PyGetSetDef 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 ~PyTypeObject.tp_dict below) containing a getset descriptor.

Inheritance:

This field is not inherited by subtypes (computed attributes are inherited through a different mechanism).

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.

For the corresponding slot ID, see Py_tp_base.

[!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, ~PyTypeObject.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 type object).

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. Once PyType_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 ~object.__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.

3.12

Internals detail: For static builtin types, this is always NULL. Instead, the dict for such types is stored on PyInterpreterState. Use PyType_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 modify ~PyTypeObject.tp_dict with the dictionary C-API.

Py_tp_descr_get

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.

Py_tp_descr_set

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.

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 ~PyTypeObject.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 ~PyTypeObject.tp_dictoffset should be regarded as write-only. To get the pointer to the dictionary call PyObject_GenericGetDict. Calling PyObject_GenericGetDict may need to allocate memory for the dictionary, so it is may be more efficient to call PyObject_GetAttr when accessing an attribute on the object.

It is an error to set both the Py_TPFLAGS_MANAGED_DICT bit and ~PyTypeObject.tp_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 <static-types>, if the field is NULL then no ~object.__dict__ gets created for instances.

If the Py_TPFLAGS_MANAGED_DICT bit is set in the ~PyTypeObject.tp_flags field, then ~PyTypeObject.tp_dictoffset will be set to -1, to indicate that it is unsafe to use this field.

Py_tp_init

An optional pointer to an instance initialization function.

This function corresponds to the ~object.__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 ~object.__init__.

The ~PyTypeObject.tp_init function, if not NULL, is called when an instance is created normally by calling its type, after the type's ~PyTypeObject.tp_new function has returned an instance of the type. If the ~PyTypeObject.tp_new function returns an instance of some other type that is not a subtype of the original type, no ~PyTypeObject.tp_init function is called; if ~PyTypeObject.tp_new returns an instance of a subtype of the original type, the subtype's ~PyTypeObject.tp_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 <static-types> this field does not have a default.

Py_tp_alloc

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 from object.

Heap subtypes <heap-types> 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).

Py_tp_new

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 ~PyTypeObject.tp_new function is called; it may be a subtype of that type (but not an unrelated type).

The ~PyTypeObject.tp_new function should call subtype->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 the ~PyTypeObject.tp_init handler. A good rule of thumb is that for immutable types, all initialization should take place in ~PyTypeObject.tp_new, while for mutable types, most initialization should be deferred to ~PyTypeObject.tp_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 <static-types> whose ~PyTypeObject.tp_base is NULL or &PyBaseObject_Type.

Default:

For static types <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.

Py_tp_free

An optional pointer to an instance deallocation function. Its signature is:

void tp_free(void *self);

This function must free the memory allocated by ~PyTypeObject.tp_alloc.

Inheritance:

Static subtypes inherit this slot, which will be PyObject_Free if inherited from object. Exception: If the type supports garbage collection (i.e., the Py_TPFLAGS_HAVE_GC flag is set in ~PyTypeObject.tp_flags) and it would inherit PyObject_Free, then this slot is not inherited but instead defaults to PyObject_GC_Del.

Heap subtypes <heap-types> do not inherit this slot.

Default:

For heap subtypes <heap-types>, this slot defaults to a deallocator suitable to match PyType_GenericAlloc and the value of the Py_TPFLAGS_HAVE_GC flag.

For static subtypes, this slot is inherited (see above).

Py_tp_is_gc

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 ~PyTypeObject.tp_flags field, and check the Py_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 return 1 for a collectible instance, and 0 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 <heap-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.

Tuple of base types.

This field should be set to NULL and treated as read-only. Python will fill it in when the type is initialized <PyType_Ready>.

For the corresponding slot ID, see Py_tp_bases.

[!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.

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 is initialized <PyType_Ready>.

Inheritance:

This field is not inherited; it is calculated fresh by PyType_Ready.

Unused. Internal use only.

Inheritance:

This field is not inherited.

A collection of subclasses. Internal use only. May be an invalid pointer.

To get a list of subclasses, call the Python method ~type.__subclasses__.

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.

Weak reference list head, for weak references to this type object. Not inherited. Internal use only.

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 on PyInterpreterState. Use the public C-API or the internal _PyObject_GET_WEAKREFS_LISTPTR() macro to avoid the distinction.

Inheritance:

This field is not inherited.

Py_tp_del

This field is deprecated. Use ~PyTypeObject.tp_finalize instead.

Used to index into the method cache. Internal use only.

Inheritance:

This field is not inherited.

Py_tp_finalize

An optional pointer to an instance finalization function. This is the C implementation of the ~object.__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 (~PyTypeObject.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 (~PyTypeObject.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 (~PyTypeObject.tp_dealloc) is called. It is recommended to call PyObject_CallFinalizerFromDealloc at the beginning of !tp_dealloc to guarantee that the object is always finalized before destruction.

[!NOTE] The ~PyTypeObject.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 ~object.__del__ method for details.

When Python finalizes an object, it behaves like the following algorithm:

1. 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 in ~PyTypeObject.tp_flags) and never marks other types of objects; this might change in a future version.
2. If the object is not marked as finalized and its !tp_finalize finalizer function is non-NULL, the finalizer function is called.
3. 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.
4. 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 or PyObject_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 calling PyObject_CallFinalizer or PyObject_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 (~PyTypeObject.tp_clear) the object.
• If an object is a member of a cyclic isolate, Python will not automatically finalize it after automatically clearing (see ~PyTypeObject.tp_clear) any other member.
• Python will automatically finalize every member of a cyclic isolate before it automatically clears (see ~PyTypeObject.tp_clear) any of them.
• If Python is going to automatically clear an object (~PyTypeObject.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 or PyObject_CallFinalizerFromDealloc instead.

~PyTypeObject.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 calling PyErr_GetRaisedException and restore the exception at the end by calling PyErr_SetRaisedException. If an exception is encountered in the middle of the finalizer, log and clear it with PyErr_WriteUnraisable or PyErr_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.

3.4

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.

• 442: "Safe object finalization"
• life-cycle for details about how this slot relates to other slots.
• PyObject_CallFinalizer
• PyObject_CallFinalizerFromDealloc

Py_tp_vectorcall

A vectorcall function <vectorcall> to use for calls of this type object (rather than instances). In other words, tp_vectorcall can be used to optimize type.__call__, which typically returns a new instance of type.

As with any vectorcall function, if tp_vectorcall is NULL, the tp_call protocol (Py_TYPE(type)->tp_call) is used instead.

[!NOTE] The vectorcall protocol <vectorcall> requires that the vectorcall function has the same behavior as the corresponding tp_call. This means that type->tp_vectorcall must match the behavior of Py_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 of tp_new, and
• returns the result of tp_new.

Typically, tp_vectorcall is overridden to optimize this process for specific ~PyTypeObject.tp_new and ~PyTypeObject.tp_init. When doing this for user-subclassable types, note that both can be overridden (using ~object.__new__ and ~object.__init__, respectively).

Inheritance:

This field is never inherited.

3.9 (the field exists since 3.8 but it's only used since 3.9)

Internal. Do not use.

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 <sub-interpreter-support>, so they should not include any subinterpreter-specific state.

Also, since PyTypeObject is only part of the Limited API <limited-c-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 <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

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 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 return NULL and set an exception.

[!NOTE] The ~PyNumberMethods.nb_reserved field should always be NULL. It was previously called !nb_long, and was renamed in Python 3.0.1.

Py_nb_add

Py_nb_subtract

Py_nb_multiply

Py_nb_remainder

Py_nb_divmod

Py_nb_power

Py_nb_negative

Py_nb_positive

Py_nb_absolute

Py_nb_bool

Py_nb_invert

Py_nb_lshift

Py_nb_rshift

Py_nb_and

Py_nb_xor

Py_nb_or

Py_nb_int

Py_nb_float

Py_nb_inplace_add

Py_nb_inplace_subtract

Py_nb_inplace_multiply

Py_nb_inplace_remainder

Py_nb_inplace_power

Py_nb_inplace_lshift

Py_nb_inplace_rshift

Py_nb_inplace_and

Py_nb_inplace_xor

Py_nb_inplace_or

Py_nb_floor_divide

Py_nb_true_divide

Py_nb_inplace_floor_divide

Py_nb_inplace_true_divide

Py_nb_index

Py_nb_matrix_multiply

Py_nb_inplace_matrix_multiply

Mapping Object Structures

This structure holds pointers to the functions which an object uses to implement the mapping protocol. It has three members:

Py_mp_length

This function is used by PyMapping_Size and PyObject_Size, and has the same signature. This slot may be set to NULL if the object has no defined length.

Py_mp_subscript

This function is used by PyObject_GetItem and PySequence_GetSlice, and has the same signature as !PyObject_GetItem. This slot must be filled for the PyMapping_Check function to return 1, it can be NULL otherwise.

Py_mp_ass_subscript

This function is used by PyObject_SetItem, PyObject_DelItem, PySequence_SetSlice and PySequence_DelSlice. It has the same signature as !PyObject_SetItem, but v can also be set to NULL to delete an item. If this slot is NULL, the object does not support item assignment and deletion.

Sequence Object Structures

This structure holds pointers to the functions which an object uses to implement the sequence protocol.

Py_sq_length

This function is used by PySequence_Size and PyObject_Size, and has the same signature. It is also used for handling negative indices via the ~PySequenceMethods.sq_item and the ~PySequenceMethods.sq_ass_item slots.

Py_sq_concat

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 the ~PyNumberMethods.nb_add slot.

Py_sq_repeat

This function is used by PySequence_Repeat and has the same signature. It is also used by the * operator, after trying numeric multiplication via the ~PyNumberMethods.nb_multiply slot.

Py_sq_item

This function is used by PySequence_GetItem and has the same signature. It is also used by PyObject_GetItem, after trying the subscription via the ~PyMappingMethods.mp_subscript slot. This slot must be filled for the PySequence_Check function to return 1, it can be NULL otherwise.

Negative indexes are handled as follows: if the ~PySequenceMethods.sq_length slot is filled, it is called and the sequence length is used to compute a positive index which is passed to ~PySequenceMethods.sq_item. If !sq_length is NULL, the index is passed as is to the function.

Py_sq_ass_item

This function is used by PySequence_SetItem and has the same signature. It is also used by PyObject_SetItem and PyObject_DelItem, after trying the item assignment and deletion via the ~PyMappingMethods.mp_ass_subscript slot. This slot may be left to NULL if the object does not support item assignment and deletion.

Py_sq_contains

This function may be used by PySequence_Contains and has the same signature. This slot may be left to NULL, in this case !PySequence_Contains simply traverses the sequence until it finds a match.

Py_sq_inplace_concat

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 to NULL, in this case !PySequence_InPlaceConcat will fall back to PySequence_Concat. It is also used by the augmented assignment +=, after trying numeric in-place addition via the ~PyNumberMethods.nb_inplace_add slot.

Py_sq_inplace_repeat

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 to NULL, in this case !PySequence_InPlaceRepeat will fall back to PySequence_Repeat. It is also used by the augmented assignment *=, after trying numeric in-place multiplication via the ~PyNumberMethods.nb_inplace_multiply slot.

Buffer Object Structures

This structure holds pointers to the functions required by the Buffer protocol <bufferobjects>. The protocol defines how an exporter object can expose its internal data to consumer objects.

Py_bf_getbuffer

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:

1. Check if the request can be met. If not, raise BufferError, set view->obj to NULL and return -1.
2. Fill in the requested fields.
3. Increment an internal counter for the number of exports.
4. Set view->obj to exporter and increment view->obj.
5. Return 0.

Thread safety:

In the free-threaded build, implementations must ensure:

• The export counter increment in step (3) is atomic.
• The underlying buffer data remains valid and at a stable memory location for the lifetime of all exports.
• For objects that support resizing or reallocation (such as bytearray), the export counter is checked atomically before such operations, and BufferError is raised if exports exist.
• The function is safe to call concurrently from multiple threads.

See also thread-safety-memoryview for the Python-level thread safety guarantees of memoryview objects.

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 <buffer-structure>, the rules how an exporter must react to specific requests are in section Buffer request types <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. ~Py_buffer.format, ~Py_buffer.shape, ~Py_buffer.strides, ~Py_buffer.suboffsets and ~Py_buffer.internal 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.

Py_bf_releasebuffer

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 be NULL. Otherwise, a standard implementation of this function will take these optional steps:

1. Decrement an internal counter for the number of exports.
2. If the counter is 0, free all memory associated with view.

Thread safety:

In the free-threaded build:

• The export counter decrement in step (1) must be atomic.
• Resource cleanup when the counter reaches zero must be done atomically, as the final release may race with concurrent releases from other threads and deallocation must only happen once.

The exporter MUST use the ~Py_buffer.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

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;

Py_am_await

The signature of this function is:

PyObject *am_await(PyObject *self);

The returned object must be an iterator, i.e. PyIter_Check must return 1 for it.

This slot may be set to NULL if an object is not an awaitable.

Py_am_aiter

The signature of this function is:

PyObject *am_aiter(PyObject *self);

Must return an asynchronous iterator object. See ~object.__anext__ for details.

This slot may be set to NULL if an object does not implement asynchronous iteration protocol.

Py_am_anext

The signature of this function is:

PyObject *am_anext(PyObject *self);

Must return an awaitable object. See ~object.__anext__ for details. This slot may be set to NULL.

Py_am_send

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 to NULL.

3.10

Slot Type typedefs

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 ~PyObject.ob_refcnt set to 1 and ~PyObject.ob_type set to the type argument. If the type's ~PyTypeObject.tp_itemsize is non-zero, the object's ~PyVarObject.ob_size field should be initialized to nitems and the length of the allocated memory block should be tp_basicsize + nitems*tp_itemsize, rounded up to a multiple of sizeof(void*); otherwise, nitems is not used and the length of the block should be ~PyTypeObject.tp_basicsize.

This function should not do any other instance initialization, not even to allocate additional memory; that should be done by ~PyTypeObject.tp_new.

See ~PyTypeObject.tp_free.

See ~PyTypeObject.tp_new.

See ~PyTypeObject.tp_init.

See ~PyTypeObject.tp_repr.

Return the value of the named attribute for the object.

Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.

Return the value of the named attribute for the object.

See ~PyTypeObject.tp_getattro.

Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.

See ~PyTypeObject.tp_setattro.

See ~PyTypeObject.tp_descr_get.

See ~PyTypeObject.tp_descr_set.

See ~PyTypeObject.tp_hash.

See ~PyTypeObject.tp_richcompare.

See ~PyTypeObject.tp_iter.

See ~PyTypeObject.tp_iternext.

See ~PyAsyncMethods.am_send.

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-new-types and new-types-topics.

A basic static type <static-types>:

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 <static-types> 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 <static-types> 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 *),
};