Type Objects¶
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 |
||||
---|---|---|---|---|---|---|
O |
T |
D |
I |
|||
<R> |
const char * |
__name__ |
X |
X |
||
X |
X |
X |
||||
X |
X |
|||||
X |
X |
X |
||||
X |
X |
|||||
__getattribute__, __getattr__ |
G |
|||||
__setattr__, __delattr__ |
G |
|||||
% |
||||||
__repr__ |
X |
X |
X |
|||
% |
||||||
% |
||||||
% |
||||||
__hash__ |
X |
G |
||||
__call__ |
X |
X |
||||
__str__ |
X |
X |
||||
__getattribute__, __getattr__ |
X |
X |
G |
|||
__setattr__, __delattr__ |
X |
X |
G |
|||
% |
||||||
unsigned long |
X |
X |
? |
|||
const char * |
__doc__ |
X |
X |
|||
X |
G |
|||||
X |
G |
|||||
__lt__, __le__, __eq__, __ne__, __gt__, __ge__ |
X |
G |
||||
X |
? |
|||||
__iter__ |
X |
|||||
__next__ |
X |
|||||
|
X |
X |
||||
|
X |
|||||
|
X |
X |
||||
__base__ |
X |
|||||
|
__dict__ |
? |
||||
__get__ |
X |
|||||
__set__, __delete__ |
X |
|||||
X |
? |
|||||
__init__ |
X |
X |
X |
|||
X |
? |
? |
||||
__new__ |
X |
X |
? |
? |
||
X |
X |
? |
? |
|||
X |
X |
|||||
< |
|
__bases__ |
~ |
|||
< |
|
__mro__ |
~ |
|||
[ |
|
|||||
|
__subclasses__ |
|||||
|
||||||
( |
||||||
unsigned int |
||||||
__del__ |
X |
|||||
- 1
A slot name in parentheses indicates it is (effectively) deprecated. Names in angle brackets should be 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 |
special methods |
|
---|---|---|
__await__ |
||
__aiter__ |
||
__anext__ |
||
__add__ __radd__ |
||
__iadd__ |
||
__sub__ __rsub__ |
||
__isub__ |
||
__mul__ __rmul__ |
||
__imul__ |
||
__mod__ __rmod__ |
||
__imod__ |
||
__divmod__ __rdivmod__ |
||
__pow__ __rpow__ |
||
__ipow__ |
||
__neg__ |
||
__pos__ |
||
__abs__ |
||
__bool__ |
||
__invert__ |
||
__lshift__ __rlshift__ |
||
__ilshift__ |
||
__rshift__ __rrshift__ |
||
__irshift__ |
||
__and__ __rand__ |
||
__iand__ |
||
__xor__ __rxor__ |
||
__ixor__ |
||
__or__ __ror__ |
||
__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__ |
||
slot typedefs¶
typedef |
Parameter Types |
Return Type |
---|---|---|
|
||
void * |
void |
|
void * |
void |
|
int |
||
|
||
int |
||
|
|
|
PyObject *const char *
|
|
|
int |
||
|
||
int |
||
|
||
int |
||
|
Py_hash_t |
|
|
||
|
|
|
|
|
|
|
||
int |
||
void |
||
void * |
int |
|
PyObject * |
|
|
|
||
|
||
|
||
int |
||
int |
||
int |
See Slot Type typedefs below for more detail.
PyTypeObject Definition¶
The structure definition for PyTypeObject
can be found in
Include/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 */
struct PyMethodDef *tp_methods;
struct PyMemberDef *tp_members;
struct PyGetSetDef *tp_getset;
// Strong reference on a heap type, borrowed reference on a static type
struct _typeobject *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;
PyObject *tp_subclasses;
PyObject *tp_weaklist;
destructor tp_del;
/* Type attribute cache version tag. Added in version 2.6 */
unsigned int tp_version_tag;
destructor tp_finalize;
vectorcallfunc tp_vectorcall;
} 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.
-
Py_ssize_t
PyObject
.
ob_refcnt
¶ This is the type object’s reference count, 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.
-
PyTypeObject *
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 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.
-
PyObject *
PyObject
.
_ob_next
¶ -
PyObject *
PyObject
.
_ob_prev
¶ These fields are only present when the macro
Py_TRACE_REFS
is defined (see theconfigure --with-trace-refs option
).Their initialization to
NULL
is taken care of by thePyObject_HEAD_INIT
macro. For statically allocated objects, these fields always remainNULL
. For dynamically allocated objects, these two fields are used to link the object into a doubly-linked list of all live objects on the heap.This could be used for various debugging purposes; currently the only uses are the
sys.getobjects()
function and to print the objects that are still alive at the end of a run when the environment variablePYTHONDUMPREFS
is set.Inheritance:
These fields are not inherited by subtypes.
PyVarObject Slots¶
-
Py_ssize_t
PyVarObject
.
ob_size
¶ For statically allocated type objects, this should be initialized to zero. For dynamically allocated type objects, this field has a special internal meaning.
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
.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. The value of N is typically stored in the instance’sob_size
field. There are exceptions: for example, ints use a negativeob_size
to indicate a negative number, and N isabs(ob_size)
there. Also, the presence of anob_size
field in the instance layout doesn’t mean that the instance structure is variable-length (for example, the structure for the list type has fixed-length instances, yet those instances have a meaningfulob_size
field).The basic size includes the fields in the instance declared by the macro
PyObject_HEAD
orPyObject_VAR_HEAD
(whichever is used to declare the instance struct) and this in turn includes the_ob_prev
and_ob_next
fields if they are present. This means that the only correct way to get an initializer for thetp_basicsize
is to use thesizeof
operator on the struct used to declare the instance layout. The basic size does not include the GC header size.A note about alignment: if the variable items require a particular alignment, this should be taken care of by the value of
tp_basicsize
. Example: suppose a type implements an array ofdouble
.tp_itemsize
issizeof(double)
. It is the programmer’s responsibility thattp_basicsize
is a multiple ofsizeof(double)
(assuming this is the alignment requirement fordouble
).For any type with variable-length instances, this field must not be
NULL
.Inheritance:
These fields are inherited separately by subtypes. 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
¶ A pointer to the instance destructor function. This function must be defined unless the type guarantees that its instances will never be deallocated (as is the case for the singletons
None
andEllipsis
). The function signature is:void tp_dealloc(PyObject *self);
The destructor function is called by the
Py_DECREF()
andPy_XDECREF()
macros when the new reference count is zero. At this point, the instance is still in existence, but there are no references to it. The destructor function should free all references which the instance owns, free all memory buffers owned by the instance (using the freeing function corresponding to the allocation function used to allocate the buffer), and call the type’stp_free
function. If the type is not subtypable (doesn’t have thePy_TPFLAGS_BASETYPE
flag bit set), it is permissible to call the object deallocator directly instead of viatp_free
. The object deallocator should be the one used to allocate the instance; this is normallyPyObject_Del()
if the instance was allocated usingPyObject_New()
orPyObject_VarNew()
, orPyObject_GC_Del()
if the instance was allocated usingPyObject_GC_New()
orPyObject_GC_NewVar()
.If the type supports garbage collection (has the
Py_TPFLAGS_HAVE_GC
flag bit set), the destructor should callPyObject_GC_UnTrack()
before clearing any member fields.static void foo_dealloc(foo_object *self) { PyObject_GC_UnTrack(self); Py_CLEAR(self->ref); Py_TYPE(self)->tp_free((PyObject *)self); }
Finally, if the type is heap allocated (
Py_TPFLAGS_HEAPTYPE
), the deallocator should decrement the reference count for its type object after calling the type deallocator. In order to avoid dangling pointers, the recommended way to achieve this is:static void foo_dealloc(foo_object *self) { PyTypeObject *tp = Py_TYPE(self); // free references and buffers here tp->tp_free(self); Py_DECREF(tp); }
Inheritance:
This field is inherited by subtypes.
-
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()
.Warning
It is not recommended for 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.Note
The semantics of the
tp_vectorcall_offset
slot are provisional and expected to be finalized in Python 3.9. If you use vectorcall, plan for updating your code for Python 3.9.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.Inheritance:
This field is always inherited. However, the
Py_TPFLAGS_HAVE_VECTORCALL
flag is not always inherited. If it’s not, then the subclass won’t use vectorcall, except whenPyVectorcall_Call()
is explicitly called. This is in particular the case for heap types (including subclasses defined in Python).
-
getattrfunc
PyTypeObject
.
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
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
¶ 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.
New 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
¶ 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
¶ 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
.
-
ternaryfunc
PyTypeObject
.
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 forPyObject_Call()
:PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);
Inheritance:
This field is inherited by subtypes.
-
reprfunc
PyTypeObject
.
tp_str
¶ 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
¶ 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:
PyBaseObject_Type
usesPyObject_GenericGetAttr()
.
-
setattrofunc
PyTypeObject
.
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 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:
PyBaseObject_Type
usesPyObject_GenericSetAttr()
.
-
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).Inheritance:
???
-
Py_TPFLAGS_BASETYPE
¶ 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
¶ This bit is set when the object supports garbage collection. If this bit is set, instances must be created using
PyObject_GC_New()
and destroyed usingPyObject_GC_Del()
. More information in section Supporting Cyclic Garbage Collection. This bit also implies that the GC-related fieldstp_traverse
andtp_clear
are present in the type object.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
¶ 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
¶ 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
.New in version 3.8.
Inheritance:
This flag is never inherited by heap types. For extension types, it is inherited whenever
tp_descr_get
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
¶ These flags are used by functions such as
PyLong_Check()
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.New 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
¶ This bit is set when the class implements the vectorcall protocol. See
tp_vectorcall_offset
for details.Inheritance:
This bit is inherited for static subtypes if
tp_call
is also inherited. Heap types do not inheritPy_TPFLAGS_HAVE_VECTORCALL
.New in version 3.9.
-
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.
New 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.
New 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
New 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
New in version 3.10.
-
-
const char *
PyTypeObject
.
tp_doc
¶ 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
¶ 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(localobject *self, visitproc visit, void *arg) { 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.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).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.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
¶ An optional pointer to a clear function for the garbage collector. This is only used if the
Py_TPFLAGS_HAVE_GC
flag bit is set. The signature is:int tp_clear(PyObject *);
The
tp_clear
member function is used to break reference cycles in cyclic garbage detected by the garbage collector. Taken together, alltp_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 must be sufficient to break 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(localobject *self) { 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 decremented until after the pointer to the contained object is set toNULL
. This is because decrementing the reference count 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.Note that
tp_clear
is not always called before an instance is deallocated. For example, when reference counting is enough to determine that an object is no longer used, the cyclic garbage collector is not involved andtp_dealloc
is called directly.Because the goal of
tp_clear
functions is to break reference cycles, it’s not necessary to clear contained objects like Python strings or Python integers, which can’t participate in reference cycles. On the other hand, it may be convenient to clear all contained Python objects, and write the type’stp_dealloc
function to invoketp_clear
.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.
-
richcmpfunc
PyTypeObject
.
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
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 return value’s reference count is properly incremented.
On error, sets an exception and returns
NULL
from the function.New 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_ssize_t
PyTypeObject
.
tp_weaklistoffset
¶ 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 toNULL
.Do not confuse this field with
tp_weaklist
; that is the list head for weak references to the type object itself.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.When a type defined by a class statement has no
__slots__
declaration, and none of its base types are weakly referenceable, the type is made weakly referenceable by adding a weak reference list head slot to the instance layout and setting thetp_weaklistoffset
of that slot’s offset.When a type’s
__slots__
declaration contains a slot named__weakref__
, that slot becomes the weak reference list head for instances of the type, and the slot’s offset is stored in the type’stp_weaklistoffset
.When a type’s
__slots__
declaration does not contain a slot named__weakref__
, the type inherits itstp_weaklistoffset
from its base type.
-
getiterfunc
PyTypeObject
.
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.
-
iternextfunc
PyTypeObject
.
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, 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
¶ 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
¶ 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
¶ 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
¶ 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__()
).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
¶ 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
¶ 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
¶ 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.If the value of this field is greater than zero, it specifies the offset from the start of the instance structure. If the value is less than zero, it specifies the offset from the end of the instance structure. A negative offset is more expensive to use, and should only be used when the instance structure contains a variable-length part. This is used for example to add an instance variable dictionary to subtypes of
str
ortuple
. Note that thetp_basicsize
field should account for the dictionary added to the end in that case, even though the dictionary is not included in the basic object layout. On a system with a pointer size of 4 bytes,tp_dictoffset
should be set to-4
to indicate that the dictionary is at the very end of the structure.The real dictionary offset in an instance can be computed from a negative
tp_dictoffset
as follows:dictoffset = tp_basicsize + abs(ob_size)*tp_itemsize + tp_dictoffset if dictoffset is not aligned on sizeof(void*): round up to sizeof(void*)
where
tp_basicsize
,tp_itemsize
andtp_dictoffset
are taken from the type object, andob_size
is taken from the instance. The absolute value is taken because ints use the sign ofob_size
to store the sign of the number. (There’s never a need to do this calculation yourself; it is done for you by_PyObject_GetDictPtr()
.)Inheritance:
This field is inherited by subtypes, but see the rules listed below. A subtype may override this offset; this means that the subtype instances store the dictionary at a difference offset than the base type. Since the dictionary is always found via
tp_dictoffset
, this should not be a problem.When a type defined by a class statement has no
__slots__
declaration, and none of its base types has an instance variable dictionary, a dictionary slot is added to the instance layout and thetp_dictoffset
is set to that slot’s offset.When a type defined by a class statement has a
__slots__
declaration, the type inherits itstp_dictoffset
from its base type.(Adding a slot named
__dict__
to the__slots__
declaration does not have the expected effect, it just causes confusion. Maybe this should be added as a feature just like__weakref__
though.)Default:
This slot has no default. For static types, if the field is
NULL
then no__dict__
gets created for instances.
-
initproc
PyTypeObject
.
tp_init
¶ 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
¶ An optional pointer to an instance allocation function.
The function signature is:
PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);
Inheritance:
This field is inherited by static subtypes, but not by dynamic subtypes (subtypes created by a class statement).
Default:
For dynamic subtypes, this field is always set to
PyType_GenericAlloc()
, to force a standard heap allocation strategy.For static subtypes,
PyBaseObject_Type
usesPyType_GenericAlloc()
. That is the recommended value for all statically defined types.
-
newfunc
PyTypeObject
.
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
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
¶ An optional pointer to an instance deallocation function. Its signature is:
void tp_free(void *self);
An initializer that is compatible with this signature is
PyObject_Free()
.Inheritance:
This field is inherited by static subtypes, but not by dynamic subtypes (subtypes created by a class statement)
Default:
In dynamic subtypes, this field is set to a deallocator suitable to match
PyType_GenericAlloc()
and the value of thePy_TPFLAGS_HAVE_GC
flag bit.For static subtypes,
PyBaseObject_Type
uses PyObject_Del.
-
inquiry
PyTypeObject
.
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
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
¶ Tuple of base types.
This is set for types created by a class statement. It should be
NULL
for statically defined types.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.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.
-
PyObject *
PyTypeObject
.
tp_subclasses
¶ List of weak references to subclasses. Internal use only.
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.
Inheritance:
This field is not inherited.
-
destructor
PyTypeObject
.
tp_del
¶ 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
¶ An optional pointer to an instance finalization function. Its signature is:
void tp_finalize(PyObject *self);
If
tp_finalize
is set, the interpreter calls it once when finalizing an instance. It is called either from the garbage collector (if the instance is part of an isolated reference cycle) or just before the object is deallocated. Either way, it is guaranteed to be called before attempting to break reference cycles, ensuring that it finds the object in a sane state.tp_finalize
should not mutate the current exception status; therefore, a recommended way to write a non-trivial finalizer is:static void local_finalize(PyObject *self) { PyObject *error_type, *error_value, *error_traceback; /* Save the current exception, if any. */ PyErr_Fetch(&error_type, &error_value, &error_traceback); /* ... */ /* Restore the saved exception. */ PyErr_Restore(error_type, error_value, error_traceback); }
For this field to be taken into account (even through inheritance), you must also set the
Py_TPFLAGS_HAVE_FINALIZE
flags bit.Also, note that, in a garbage collected Python,
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 will own the Global Interpreter Lock (GIL). However, if the object being destroyed in turn destroys objects from some other C or 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.
New in version 3.4.
See also
“Safe object finalization” (PEP 442)
-
vectorcallfunc
PyTypeObject
.
tp_vectorcall
¶ Vectorcall function to use for calls of this type object. In other words, it is used to implement vectorcall for
type.__call__
. Iftp_vectorcall
isNULL
, the default call implementation using__new__
and__init__
is used.Inheritance:
This field is never inherited.
New in version 3.9: (the field exists since 3.8 but it’s only used since 3.9)
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 not part of the stable ABI,
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()
,
or PyType_FromModuleAndSpec()
.
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
¶
-
binaryfunc
PyNumberMethods
.
nb_subtract
¶
-
binaryfunc
PyNumberMethods
.
nb_multiply
¶
-
binaryfunc
PyNumberMethods
.
nb_remainder
¶
-
binaryfunc
PyNumberMethods
.
nb_divmod
¶
-
ternaryfunc
PyNumberMethods
.
nb_power
¶
-
unaryfunc
PyNumberMethods
.
nb_negative
¶
-
unaryfunc
PyNumberMethods
.
nb_positive
¶
-
unaryfunc
PyNumberMethods
.
nb_absolute
¶
-
inquiry
PyNumberMethods
.
nb_bool
¶
-
unaryfunc
PyNumberMethods
.
nb_invert
¶
-
binaryfunc
PyNumberMethods
.
nb_lshift
¶
-
binaryfunc
PyNumberMethods
.
nb_rshift
¶
-
binaryfunc
PyNumberMethods
.
nb_and
¶
-
binaryfunc
PyNumberMethods
.
nb_xor
¶
-
binaryfunc
PyNumberMethods
.
nb_or
¶
-
unaryfunc
PyNumberMethods
.
nb_int
¶
-
void *
PyNumberMethods
.
nb_reserved
¶
-
unaryfunc
PyNumberMethods
.
nb_float
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_add
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_subtract
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_multiply
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_remainder
¶
-
ternaryfunc
PyNumberMethods
.
nb_inplace_power
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_lshift
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_rshift
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_and
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_xor
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_or
¶
-
binaryfunc
PyNumberMethods
.
nb_floor_divide
¶
-
binaryfunc
PyNumberMethods
.
nb_true_divide
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_floor_divide
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_true_divide
¶
-
unaryfunc
PyNumberMethods
.
nb_index
¶
-
binaryfunc
PyNumberMethods
.
nb_matrix_multiply
¶
-
binaryfunc
PyNumberMethods
.
nb_inplace_matrix_multiply
¶
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
¶ 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
¶ This function is used by
PyObject_GetItem()
andPySequence_GetSlice()
, and has the same signature as !PyObject_GetItem. This slot must be filled for thePyMapping_Check()
function to return1
, it can beNULL
otherwise.
-
objobjargproc
PyMappingMethods
.
mp_ass_subscript
¶ This function is used by
PyObject_SetItem()
,PyObject_DelItem()
,PyObject_SetSlice()
andPyObject_DelSlice()
. It has the same signature as !PyObject_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
¶ 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
¶ 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
¶ 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
¶ 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
¶ 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
¶ This function may be used by
PySequence_Contains()
and has the same signature. This slot may be left toNULL
, in this case !PySequence_Contains simply traverses the sequence until it finds a match.
-
binaryfunc
PySequenceMethods
.
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 toNULL
, in this case !PySequence_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
¶ 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 case !PySequence_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 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
PyExc_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 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¶
New 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 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 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 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 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
.New 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 *(*
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_descrget
.
-
typedef int (*
descrsetfunc
)(PyObject*, PyObject*, PyObject*)¶ - Part of the Stable ABI.
See
tp_descrset
.
-
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 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)¶ - 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;
PyObject *inst_dict;
PyObject *weakreflist;
} 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_weaklistoffset = offsetof(MyObject, weakreflist),
.tp_dictoffset = offsetof(MyObject, inst_dict),
.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
.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 *),
};