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
.
special methods/attrs
Info 2
O
T
D
I
<R> tp_name
const char *
__name__
X
X
Py_ssize_t
X
X
X
Py_ssize_t
X
X
X
X
X
Py_ssize_t
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
Py_ssize_t
X
?
__iter__
X
__next__
X
PyMethodDef
[]
X
X
PyMemberDef
[]
X
PyGetSetDef
[]
X
X
__base__
X
PyObject
*
__dict__
?
__get__
X
__set__, __delete__
X
Py_ssize_t
X
?
__init__
X
X
X
X
?
?
__new__
X
X
?
?
X
X
?
?
X
X
<tp_bases
>
PyObject
*
__bases__
~
<tp_mro
>
PyObject
*
__mro__
~
[tp_cache
]
PyObject
*
PyObject
*
__subclasses__
PyObject
*
(tp_del
)
unsigned int
__del__
X
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
).
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.
Slot
special methods
__await__
__aiter__
__anext__
__add__ __radd__
__iadd__
__sub__ __rsub__
__sub__
__mul__ __rmul__
__mul__
__mod__ __rmod__
__mod__
__divmod__ __rdivmod__
__pow__ __rpow__
__pow__
__neg__
__pos__
__abs__
__bool__
__invert__
__lshift__ __rlshift__
__lshift__
__rshift__ __rrshift__
__rshift__
__and__ __rand__
__and__
__xor__ __rxor__
__xor__
__or__ __ror__
__or__
__int__
void *
__float__
__floordiv__
__floordiv__
__truediv__
__truediv__
__index__
__matmul__ __rmatmul__
__matmul__
__len__
__getitem__
__setitem__, __delitem__
__len__
__add__
__mul__
__getitem__
__setitem__ __delitem__
__contains__
__iadd__
__imul__
typedef | Parameter Types | Return Type |
---|---|---|
allocfunc
|
Py_ssize_t |
PyObject *
|
destructor
|
void * | void |
freefunc
|
void * | void |
traverseproc
|
int | |
newfunc
|
PyObject *
| |
initproc
|
int | |
reprfunc
|
PyObject *
|
PyObject *
|
getattrfunc
|
const char * |
PyObject *
|
setattrfunc
|
int | |
getattrofunc
|
PyObject *
| |
setattrofunc
|
int | |
descrgetfunc
|
PyObject *
| |
descrsetfunc
|
int | |
hashfunc
|
PyObject *
|
Py_hash_t |
richcmpfunc
|
PyObject *
| |
getiterfunc
|
PyObject *
|
PyObject *
|
iternextfunc
|
PyObject *
|
PyObject *
|
lenfunc
|
PyObject *
|
Py_ssize_t |
getbufferproc
|
int | |
releasebufferproc
|
void | |
inquiry
|
void * | int |
unaryfunc
|
|
PyObject *
|
binaryfunc
|
PyObject *
| |
ternaryfunc
|
PyObject *
| |
ssizeargfunc
|
Py_ssize_t |
PyObject *
|
ssizeobjargproc
|
Py_ssize_t |
int |
objobjproc
|
int | |
objobjargproc
|
int |
See Slot Type typedefs below for more detail.
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 */
/* call function for all accessible objects */
traverseproc tp_traverse;
/* delete references to contained objects */
inquiry tp_clear;
/* 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;
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;
} PyTypeObject;
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.
PyObject._ob_next
PyObject._ob_prev
These fields are only present when the macro Py_TRACE_REFS
is defined.
Their initialization to NULL
is taken care of by the PyObject_HEAD_INIT
macro. For statically allocated objects, these fields always remain NULL
.
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 use is to print the objects
that are still alive at the end of a run when the environment variable
PYTHONDUMPREFS
is set.
Inheritance:
These fields are not inherited by subtypes.
PyObject.ob_refcnt
This is the type object’s reference count, initialized to 1
by the
PyObject_HEAD_INIT
macro. Note that for statically allocated type objects,
the type’s instances (objects whose ob_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.
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 ob_type
is NULL
, and if so,
initializes it to the 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.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.
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.)
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 module M
in subpackage Q
in package P
should have the tp_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
in PyTypeObject()
(other than potentially
tp_itemsize
).
Inheritance:
This field is not inherited by subtypes.
PyTypeObject.tp_basicsize
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-zero
tp_itemsize
field. For a type with fixed-length instances, all
instances have the same size, given in tp_basicsize
.
For a type with variable-length instances, the instances must have an
ob_size
field, and the instance size is tp_basicsize
plus N
times tp_itemsize
, where N is the “length” of the object. The value of
N is typically stored in the instance’s ob_size
field. There are
exceptions: for example, ints use a negative ob_size
to indicate a
negative number, and N is abs(ob_size)
there. Also, the presence of an
ob_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 meaningful ob_size
field).
The basic size includes the fields in the instance declared by the macro
PyObject_HEAD
or PyObject_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 the tp_basicsize
is to use the
sizeof
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 of double
. tp_itemsize
is
sizeof(double)
. It is the programmer’s responsibility that
tp_basicsize
is a multiple of sizeof(double)
(assuming this is the
alignment requirement for double
).
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 set
tp_itemsize
to a different non-zero value in a subtype (though this
depends on the implementation of the base type).
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
and Ellipsis
). The function signature is:
void tp_dealloc(PyObject *self);
The destructor function is called by the Py_DECREF()
and
Py_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’s
tp_free
function. If the type is not subtypable
(doesn’t have the Py_TPFLAGS_BASETYPE
flag bit set), it is
permissible to call the object deallocator directly instead of via
tp_free
. The object deallocator should be the one used to allocate the
instance; this is normally PyObject_Del()
if the instance was allocated
using PyObject_New()
or PyObject_VarNew()
, or
PyObject_GC_Del()
if the instance was allocated using
PyObject_GC_New()
or PyObject_GC_NewVar()
.
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.
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 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 tp_call
.
Any class that sets Py_TPFLAGS_HAVE_VECTORCALL
must also set
tp_call
and make sure its behaviour is consistent
with the vectorcallfunc function.
This can be done by setting tp_call to PyVectorcall_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 when
PyVectorcall_Call()
is explicitly called.
This is in particular the case for heap types
(including subclasses defined in Python).
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 both tp_getattr
and tp_getattro
from its base type when
the subtype’s tp_getattr
and tp_getattro
are both NULL
.
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 both tp_setattr
and tp_setattro
from its base type when
the subtype’s tp_setattr
and tp_setattro
are both NULL
.
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
and tp_reserved
.
Inheritance:
The tp_as_async
field is not inherited,
but the contained fields are inherited individually.
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.
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.
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.
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.
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 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: tp_hash
, tp_richcompare
This field is inherited by subtypes together with
tp_richcompare
: a subtype inherits both of
tp_richcompare
and tp_hash
, when the subtype’s
tp_richcompare
and tp_hash
are both NULL
.
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
for PyObject_Call()
:
PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);
Inheritance:
This field is inherited by subtypes.
PyTypeObject.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.
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 both tp_getattr
and tp_getattro
from its base type when
the subtype’s tp_getattr
and tp_getattro
are both NULL
.
Default:
PyBaseObject_Type
uses PyObject_GenericGetAttr()
.
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 to
PyObject_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 both tp_setattr
and tp_setattro
from its base type when
the subtype’s tp_setattr
and tp_setattro
are both NULL
.
Default:
PyBaseObject_Type
uses PyObject_GenericSetAttr()
.
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.
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
, and
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 tp_traverse
and tp_clear
fields, i.e. if the
Py_TPFLAGS_HAVE_GC
flag bit is clear in the subtype and the
tp_traverse
and 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 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.
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, the 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).
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 using PyObject_GC_Del()
. More information in section
Supporting Cyclic Garbage Collection. This bit also implies that the
GC-related fields tp_traverse
and tp_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 the tp_traverse
and tp_clear
fields, i.e. if the Py_TPFLAGS_HAVE_GC
flag bit is
clear in the subtype and the tp_traverse
and
tp_clear
fields in the subtype exist and have NULL
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
,
Py_TPFLAGS_HAVE_VERSION_TAG
.
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)
(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
.
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, like PyObject_IsInstance()
. Custom types that inherit
from built-ins should have their tp_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 inherit Py_TPFLAGS_HAVE_VECTORCALL
.
New in version 3.9.
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.
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 a tp_traverse
function
simply calls Py_VISIT()
on each of the instance’s members that are Python
objects that the instance owns. For example, this is function local_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 a self->key
member, it can only
be NULL
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’s
get_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 the
tp_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 to
local_traverse()
to have these specific names; don’t name them just
anything.
Heap-allocated types (Py_TPFLAGS_HEAPTYPE
, such as those created
with PyType_FromSpec()
and similar APIs) hold a reference to their
type. Their traversal function must therefore either visit
Py_TYPE(self)
, or delegate this responsibility by
calling tp_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)
in
tp_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 the
Py_TPFLAGS_HAVE_GC
flag bit: the flag bit, tp_traverse
, and
tp_clear
are all inherited from the base type if they are all zero in
the subtype.
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, all tp_clear
functions in the system must combine to break all reference cycles. This is
subtle, and if in any doubt supply a tp_clear
function. For example,
the tuple type does not implement a tp_clear
function, because it’s
possible to prove that no reference cycle can be composed entirely of tuples.
Therefore the tp_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 implementing tp_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 to NULL
, 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 to NULL
. 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 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.
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’s
tp_dealloc
function to invoke tp_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 the
Py_TPFLAGS_HAVE_GC
flag bit: the flag bit, tp_traverse
, and
tp_clear
are all inherited from the base type if they are all zero in
the subtype.
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
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
tp_richcompare
and for PyObject_RichCompare()
:
Constant |
Comparison |
---|---|
|
|
|
|
|
|
|
|
|
|
|
|
The following macro is defined to ease writing rich comparison functions:
Py_RETURN_RICHCOMPARE
(VAL_A, VAL_B, op)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 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 inherits tp_richcompare
and tp_hash
when
the subtype’s tp_richcompare
and tp_hash
are both
NULL
.
Default:
PyBaseObject_Type
provides a tp_richcompare
implementation, which may be inherited. However, if only
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.
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 to NULL
.
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 the tp_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’s
tp_weaklistoffset
.
When a type’s __slots__
declaration does not contain a slot named
__weakref__
, the type inherits its tp_weaklistoffset
from its
base type.
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.
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
; a StopIteration
exception may or may not be set. When another error occurs, it must return
NULL
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.
PyTypeObject.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
tp_dict
below) containing a method descriptor.
Inheritance:
This field is not inherited by subtypes (methods are inherited through a different mechanism).
PyTypeObject.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
tp_dict
below) containing a member descriptor.
Inheritance:
This field is not inherited by subtypes (members are inherited through a different mechanism).
PyTypeObject.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
tp_dict
below) containing a getset descriptor.
Inheritance:
This field is not inherited by subtypes (computed attributes are inherited through a different mechanism).
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 type object
).
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. 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 __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 modify
tp_dict
with the dictionary C-API.
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.
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.
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
or tuple
. Note
that the tp_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
and tp_dictoffset
are
taken from the type object, and ob_size
is taken from the instance. The
absolute value is taken because ints use the sign of ob_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 the tp_dictoffset
is set to
that slot’s offset.
When a type defined by a class statement has a __slots__
declaration,
the type inherits its tp_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.
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 not NULL
, is called when an instance is
created normally by calling its type, after the type’s tp_new
function
has returned an instance of the type. If the tp_new
function returns an
instance of some other type that is not a subtype of the original type, no
tp_init
function is called; if tp_new
returns an instance of a
subtype of the original type, the subtype’s 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 this field does not have a default.
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
uses
PyType_GenericAlloc()
. That is the recommended value
for all statically defined types.
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 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 tp_init
handler. A good
rule of thumb is that for immutable types, all initialization should take place
in tp_new
, while for mutable types, most initialization should be
deferred to tp_init
.
Inheritance:
This field is inherited by subtypes, except it is not inherited by static types
whose tp_base
is NULL
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.
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 the
Py_TPFLAGS_HAVE_GC
flag bit.
For static subtypes, PyBaseObject_Type
uses PyObject_Del.
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 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.)
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.
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.
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()
.
PyTypeObject.tp_cache
Unused. Internal use only.
Inheritance:
This field is not inherited.
PyTypeObject.tp_subclasses
List of weak references to subclasses. Internal use only.
Inheritance:
This field is not inherited.
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.
PyTypeObject.tp_del
tp_finalize
instead.PyTypeObject.tp_version_tag
Used to index into the method cache. Internal use only.
Inheritance:
This field is not inherited.
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.
Inheritance:
This field is inherited by subtypes.
New in version 3.4.
See also
“Safe object finalization” (PEP 442)
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__
.
If tp_vectorcall
is NULL
, 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)
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.
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:
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.
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.
This is done by filling a PyType_Spec
structure and calling
PyType_FromSpecWithBases()
.
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 return NULL
and set an exception.
Note
The nb_reserved
field should always be NULL
. It
was previously called nb_long
, and was renamed in
Python 3.0.1.
PyNumberMethods.nb_add
PyNumberMethods.nb_subtract
PyNumberMethods.nb_multiply
PyNumberMethods.nb_remainder
PyNumberMethods.nb_divmod
PyNumberMethods.nb_power
PyNumberMethods.nb_negative
PyNumberMethods.nb_positive
PyNumberMethods.nb_absolute
PyNumberMethods.nb_bool
PyNumberMethods.nb_invert
PyNumberMethods.nb_lshift
PyNumberMethods.nb_rshift
PyNumberMethods.nb_and
PyNumberMethods.nb_xor
PyNumberMethods.nb_or
PyNumberMethods.nb_int
PyNumberMethods.nb_reserved
PyNumberMethods.nb_float
PyNumberMethods.nb_inplace_add
PyNumberMethods.nb_inplace_subtract
PyNumberMethods.nb_inplace_multiply
PyNumberMethods.nb_inplace_remainder
PyNumberMethods.nb_inplace_power
PyNumberMethods.nb_inplace_lshift
PyNumberMethods.nb_inplace_rshift
PyNumberMethods.nb_inplace_and
PyNumberMethods.nb_inplace_xor
PyNumberMethods.nb_inplace_or
PyNumberMethods.nb_floor_divide
PyNumberMethods.nb_true_divide
PyNumberMethods.nb_inplace_floor_divide
PyNumberMethods.nb_inplace_true_divide
PyNumberMethods.nb_index
PyNumberMethods.nb_matrix_multiply
PyNumberMethods.nb_inplace_matrix_multiply
PyMappingMethods
PyMappingMethods.mp_length
PyMapping_Size()
and PyObject_Size()
, and has the same signature. This slot may be set to NULL
if the object has no defined length.PyMappingMethods.mp_subscript
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.PyMappingMethods.mp_ass_subscript
PyObject_SetItem()
, PyObject_DelItem()
, PyObject_SetSlice()
and PyObject_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.
PySequenceMethods
PySequenceMethods.sq_length
PySequence_Size()
and PyObject_Size()
, and has the same signature. It is also used for handling negative indices via the sq_item
and the sq_ass_item
slots.PySequenceMethods.sq_concat
PySequence_Concat()
and has the same signature. It is also used by the +
operator, after trying the numeric addition via the nb_add
slot.PySequenceMethods.sq_repeat
PySequence_Repeat()
and has the same signature. It is also used by the *
operator, after trying numeric multiplication via the nb_multiply
slot.PySequenceMethods.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 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 sq_length
slot is
filled, it is called and the sequence length is used to compute a positive
index which is passed to sq_item
. If sq_length
is NULL
,
the index is passed as is to the function.
PySequenceMethods.sq_ass_item
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 mp_ass_subscript
slot. This slot may be left to NULL
if the object does not support item assignment and deletion.PySequenceMethods.sq_contains
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.PySequenceMethods.sq_inplace_concat
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 nb_inplace_add
slot.PySequenceMethods.sq_inplace_repeat
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 nb_inplace_multiply
slot.
PyBufferProcs
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
to NULL
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
and 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.
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 be
NULL
. 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.
New in version 3.5.
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;
} PyAsyncMethods;
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
return 1
for it.
This slot may be set to NULL
if an object is not an awaitable.
PyAsyncMethods.am_aiter
The signature of this function is:
PyObject *am_aiter(PyObject *self);
Must return an awaitable object. See __anext__()
for details.
This slot may be set to NULL
if an object does not implement
asynchronous iteration protocol.
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 to NULL
.
(*allocfunc)
(PyTypeObject *cls, Py_ssize_t nitems)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 to 1
and ob_type
set to the type argument. If
the type’s tp_itemsize
is non-zero, the object’s 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 tp_basicsize
.
This function should not do any other instance initialization, not even to
allocate additional memory; that should be done by tp_new
.
(*destructor)
(PyObject *)(*freefunc)
(void *)tp_free
.(*getattrfunc)
(PyObject *self, char *attr)(*setattrfunc)
(PyObject *self, char *attr, PyObject *value)NULL
to delete the attribute.(*getattrofunc)
(PyObject *self, PyObject *attr)Return the value of the named attribute for the object.
See tp_getattro
.
(*setattrofunc)
(PyObject *self, PyObject *attr, PyObject *value)Set the value of the named attribute for the object.
The value argument is set to NULL
to delete the attribute.
See tp_setattro
.
(*richcmpfunc)
(PyObject *, PyObject *, int)tp_richcompare
.(*iternextfunc)
(PyObject *)tp_iternext
.(*lenfunc)
(PyObject *)(*ssizeobjargproc)
(PyObject *, Py_ssize_t)
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 = "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 */
"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 = "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):
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 = "my custom str",
.tp_flags = Py_TPFLAGS_DEFAULT,
.tp_new = NULL,
.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 *),
};