Perhaps one of the most important structures of the Python object system is the structure that defines a new type: the
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
section provides at-a-glance insight into the meaning and use of
.
Quick Reference
“tp slots”
PyTypeObject Slot
special methods/attrs
Info
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__
~
[
]
*
[
]
void *
__subclasses__
[
]
*
(
)
[
]
unsigned int
__del__
X
[
]
unsigned char
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__
__buffer__
__release_buffer__
slot typedefs
typedef
Parameter Types
Return Type
*
*
*
void
void *
void
*
void *
int
*
*
*
*
*
*
*
int
*
*
*
const char *
*
*
const char *
*
int
*
*
*
*
*
*
int
*
*
*
*
*
*
*
int
*
Py_hash_t
*
*
int
*
*
*
*
*
*
*
*
int
int
*
*
void
*
int
*
*
*
*
*
*
*
*
*
*
*
*
*
int
*
*
int
*
*
*
int
See
below for more detail.
PyTypeObject Definition
The structure definition for
can be found in Include/cpython/object.h. For convenience of reference, this repeats the definition found there:
typedefstruct_typeobject{PyObject_VAR_HEADconstchar*tp_name;/* For printing, in format "<module>.<name>" */Py_ssize_ttp_basicsize,tp_itemsize;/* For allocation *//* Methods to implement standard operations */destructortp_dealloc;Py_ssize_ttp_vectorcall_offset;getattrfunctp_getattr;setattrfunctp_setattr;PyAsyncMethods*tp_as_async;/* formerly known as tp_compare (Python 2) or tp_reserved (Python 3) */reprfunctp_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) */hashfunctp_hash;ternaryfunctp_call;reprfunctp_str;getattrofunctp_getattro;setattrofunctp_setattro;/* Functions to access object as input/output buffer */PyBufferProcs*tp_as_buffer;/* Flags to define presence of optional/expanded features */unsignedlongtp_flags;constchar*tp_doc;/* Documentation string *//* Assigned meaning in release 2.0 *//* call function for all accessible objects */traverseproctp_traverse;/* delete references to contained objects */inquirytp_clear;/* Assigned meaning in release 2.1 *//* rich comparisons */richcmpfunctp_richcompare;/* weak reference enabler */Py_ssize_ttp_weaklistoffset;/* Iterators */getiterfunctp_iter;iternextfunctp_iternext;/* Attribute descriptor and subclassing stuff */PyMethodDef*tp_methods;PyMemberDef*tp_members;PyGetSetDef*tp_getset;// Strong reference on a heap type, borrowed reference on a static typePyTypeObject*tp_base;PyObject*tp_dict;descrgetfunctp_descr_get;descrsetfunctp_descr_set;Py_ssize_ttp_dictoffset;initproctp_init;allocfunctp_alloc;newfunctp_new;freefunctp_free;/* Low-level free-memory routine */inquirytp_is_gc;/* For PyObject_IS_GC */PyObject*tp_bases;PyObject*tp_mro;/* method resolution order */PyObject*tp_cache;/* no longer used */void*tp_subclasses;/* for static builtin types this is an index */PyObject*tp_weaklist;/* not used for static builtin types */destructortp_del;/* Type attribute cache version tag. Added in version 2.6. * If zero, the cache is invalid and must be initialized. */unsignedinttp_version_tag;destructortp_finalize;vectorcallfunctp_vectorcall;/* bitset of which type-watchers care about this type */unsignedchartp_watched;/* Number of tp_version_tag values used. * Set to _Py_ATTR_CACHE_UNUSED if the attribute cache is * disabled for this type (e.g. due to custom MRO entries). * Otherwise, limited to MAX_VERSIONS_PER_CLASS (defined elsewhere). */uint16_ttp_versions_used;}PyTypeObject;PyObject Slots
The type object structure extends the
structure. The
field is used for dynamic types (created by type_new(), usually called from a class statement). Note that
(the metatype) initializes
, which means that its instances (i.e. type objects) must have the ob_size field.
The type object’s reference count is initialized to 1 by the PyObject_HEAD_INIT macro. Note that for
statically allocated type objects
, the type’s instances (objects whose
points back to the type) do not count as references. But for
dynamically allocated type objects
, the instances do count as references.
Inheritance:
This field is not inherited by subtypes.
This is the type’s type, in other words its metatype. It is initialized by the argument to the PyObject_HEAD_INIT macro, and its value should normally be &PyType_Type. However, for dynamically loadable extension modules that must be usable on Windows (at least), the compiler complains that this is not a valid initializer. Therefore, the convention is to 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.
checks if
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 Slots
For
statically allocated type objects
, this should be initialized to zero. For
dynamically allocated type objects
, this field has a special internal meaning.
This field should be accessed using the
macro.
Inheritance:
This field is not inherited by subtypes.
PyTypeObject Slots
Each slot has a section describing inheritance. If
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
and
effectively act as defaults.)
constchar*
.tp_name
See
for the corresponding
.
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
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
attribute, and everything after the last dot is made accessible as the
attribute.
If no dot is present, the entire
field is made accessible as the
attribute, and the
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
(other than potentially
).
Inheritance:
This field is not inherited by subtypes.
.tp_basicsize
.tp_itemsize
These fields allow calculating the size in bytes of instances of the type.
See
,
and
for the corresponding
.
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. (Exceptions to this rule can be made using
PyUnstable_Object_GC_NewWithExtraData()
.)
For a type with variable-length instances, the instances must have an
field, and the instance size is tp_basicsize plus N times tp_itemsize, where N is the “length” of the object.
Functions like
will take the value of N as an argument, and store in the instance’s
field. Note that the ob_size field may later be used for other purposes. For example,
instances use the bits of ob_size in an implementation-defined way; the underlying storage and its size should be accessed using
.
Also, the presence of an
field in the instance layout doesn’t mean that the instance structure is variable-length. For example, the
type has fixed-length instances, yet those instances have a ob_size field. (As with
, avoid reading lists’ ob_size directly. Call
instead.)
The tp_basicsize includes size needed for data of the type’s
, plus any extra data needed by each instance.
The correct way to set tp_basicsize is to use the sizeof operator on the struct used to declare the instance layout. This struct must include the struct used to declare the base type. In other words, tp_basicsize must be greater than or equal to the base’s tp_basicsize.
Since every type is a subtype of
, this struct must include
or
(depending on whether
should be included). These are usually defined by the macro
or
, respectively.
The basic size does not include the GC header size, as that header is not part of
.
For cases where struct used to declare the base type is unknown, see
and
.
Notes about alignment:
tp_basicsize must be a multiple of _Alignof(PyObject). When using sizeof on a struct that includes
, as recommended, the compiler ensures this. When not using a C struct, or when using compiler extensions like __attribute__((packed)), it is up to you.
If the variable items require a particular alignment, tp_basicsize and tp_itemsize must each be a multiple of that alignment. For example, if a type’s variable part stores a double, it is your responsibility that both fields are a multiple of _Alignof(double).
Inheritance:
These fields are inherited separately by subtypes. (That is, if the field is set to zero,
will copy the value from the base type, indicating that the instances do not need additional storage.)
If the base type has a non-zero
, 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).
.tp_dealloc
The corresponding
Py_tp_dealloc is part of the
.
A pointer to the instance destructor function. The function signature is:
voidtp_dealloc(PyObject*self);The destructor function should remove all references which the instance owns (e.g., call
), free all memory buffers owned by the instance, and call the type’s
function to free the object itself.
If you may call functions that may set the error indicator, you must use
and
to ensure you don’t clobber a preexisting error indicator (the deallocation could have occurred while processing a different error):
staticvoidfoo_dealloc(foo_object*self){PyObject*et,*ev,*etb;PyObject*exc=PyErr_GetRaisedException();...PyErr_SetRaisedException(exc);}The dealloc handler itself must not raise an exception; if it hits an error case it should call
to log (and clear) an unraisable exception.
No guarantees are made about when an object is destroyed, except:
Python will destroy an object immediately or some time after the final reference to the object is deleted, unless its finalizer (
) subsequently resurrects the object.
An object will not be destroyed while it is being automatically finalized (
) or automatically cleared (
).
CPython currently destroys an object immediately from
when the new reference count is zero, but this may change in a future version.
It is recommended to call
PyObject_CallFinalizerFromDealloc()
at the beginning of tp_dealloc to guarantee that the object is always finalized before destruction.
If the type supports garbage collection (the
flag is set), the destructor should call
before clearing any member fields.
It is permissible to call
from tp_dealloc to reduce code duplication and to guarantee that the object is always cleared before destruction. Beware that tp_clear might have already been called.
If the type is heap allocated (
), the deallocator should release the owned reference to its type object (via
) after calling the type deallocator. See the example code below.:
staticvoidfoo_dealloc(PyObject*op){foo_object*self=(foo_object*)op;PyObject_GC_UnTrack(self);Py_CLEAR(self->ref);Py_TYPE(self)->tp_free(self);}tp_dealloc must leave the exception status unchanged. If it needs to call something that might raise an exception, the exception state must be backed up first and restored later (after logging any exceptions with
).
Example:
staticvoidfoo_dealloc(PyObject*self){PyObject*exc=PyErr_GetRaisedException();if(PyObject_CallFinalizerFromDealloc(self)<0){// self was resurrected.gotodone;}PyTypeObject*tp=Py_TYPE(self);if(tp->tp_flags&Py_TPFLAGS_HAVE_GC){PyObject_GC_UnTrack(self);}// Optional, but convenient to avoid code duplication.if(tp->tp_clear&&tp->tp_clear(self)<0){PyErr_WriteUnraisable(self);}// Any additional destruction goes here.tp->tp_free(self);self=NULL;// In case PyErr_WriteUnraisable() is called below.if(tp->tp_flags&Py_TPFLAGS_HEAPTYPE){Py_CLEAR(tp);}done:// Optional, if something was called that might have raised an// exception.if(PyErr_Occurred()){PyErr_WriteUnraisable(self);}PyErr_SetRaisedException(exc);}tp_dealloc may be called from any Python thread, not just the thread which created the object (if the object becomes part of a refcount cycle, that cycle might be collected by a garbage collection on any thread). This is not a problem for Python API calls, since the thread on which tp_dealloc is called with an
. However, if the object being destroyed in turn destroys objects from some other C library, care should be taken to ensure that destroying those objects on the thread which called tp_dealloc will not violate any assumptions of the library.
Inheritance:
This field is inherited by subtypes.
.tp_vectorcall_offset
An optional offset to a per-instance function that implements calling the object using the
, a more efficient alternative of the simpler
.
This field is only used if the flag
is set. If so, this must be a positive integer containing the offset in the instance of a
pointer.
The vectorcallfunc pointer may be NULL, in which case the instance behaves as if
was not set: calling the instance falls back to
.
Any class that sets Py_TPFLAGS_HAVE_VECTORCALL must also set
and make sure its behaviour is consistent with the vectorcallfunc function. This can be done by setting tp_call to
.
Changed in version 3.8: Before version 3.8, this slot was named tp_print. In Python 2.x, it was used for printing to a file. In Python 3.0 to 3.7, it was unused.
Changed in version 3.12: Before version 3.12, it was not recommended for
to implement the vectorcall protocol. When a user sets
in Python code, only tp_call is updated, likely making it inconsistent with the vectorcall function. Since 3.12, setting __call__ will disable vectorcall optimization by clearing the
flag.
Inheritance:
This field is always inherited. However, the
flag is not always inherited. If it’s not set, then the subclass won’t use
, except when
is explicitly called.
.tp_getattr
The corresponding
Py_tp_getattr is part of the
.
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
function, but taking a C string instead of a Python string object to give the attribute name.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits both
and tp_getattro from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.
.tp_setattr
The corresponding
Py_tp_setattr is part of the
.
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
function, but taking a C string instead of a Python string object to give the attribute name.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits both
and tp_setattro from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.
*
.tp_as_async
Pointer to an additional structure that contains fields relevant only to objects which implement
and
protocols at the C-level. See
for details.
Added in version 3.5: Formerly known as tp_compare and tp_reserved.
Inheritance:
The
field is not inherited, but the contained fields are inherited individually.
.tp_repr
The corresponding
Py_tp_repr is part of the
.
An optional pointer to a function that implements the built-in function
.
The signature is the same as for
:
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
, 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 <%sobjectat%p> is returned, where %s is replaced by the type name, and %p by the object’s memory address.
*
.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
.
Inheritance:
The
field is not inherited, but the contained fields are inherited individually.
*
.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
.
Inheritance:
The
field is not inherited, but the contained fields are inherited individually.
*
.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
.
Inheritance:
The
field is not inherited, but the contained fields are inherited individually.
.tp_hash
The corresponding
Py_tp_hash is part of the
.
An optional pointer to a function that implements the built-in function
.
The signature is the same as for
:
Py_hash_ttp_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
is not set), an attempt to take the hash of the object raises
. This is the same as setting it to
.
This field can be set explicitly to
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:
,
This field is inherited by subtypes together with
: a subtype inherits both of tp_richcompare and
, when the subtype’s tp_richcompare and tp_hash are both NULL.
Default:
uses
.
.tp_call
The corresponding
Py_tp_call is part of the
.
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*tp_call(PyObject*self,PyObject*args,PyObject*kwargs);Inheritance:
This field is inherited by subtypes.
.tp_str
The corresponding
Py_tp_str is part of the
.
An optional pointer to a function that implements the built-in operation
. (Note that
is a type now, and str() calls the constructor for that type. This constructor calls
to do the actual work, and PyObject_Str() will call this handler.)
The signature is the same as for
:
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
function.
Inheritance:
This field is inherited by subtypes.
Default:
When this field is not set,
is called to return a string representation.
.tp_getattro
The corresponding
Py_tp_getattro is part of the
.
An optional pointer to the get-attribute function.
The signature is the same as for
:
PyObject*tp_getattro(PyObject*self,PyObject*attr);It is usually convenient to set this field to
, which implements the normal way of looking for object attributes.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits both tp_getattr and
from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.
Default:
uses
.
.tp_setattro
The corresponding
Py_tp_setattro is part of the
.
An optional pointer to the function for setting and deleting attributes.
The signature is the same as for
:
inttp_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
, which implements the normal way of setting object attributes.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits both tp_setattr and
from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.
Default:
uses
.
*
.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
.
Inheritance:
The
field is not inherited, but the contained fields are inherited individually.
unsignedlong
.tp_flags
See
for the corresponding
.
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
,
,
, and
) 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
flag bit is inherited together with the
and
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:
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
field. The macro
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
. In this case, the
field of its instances is considered a reference to the type, and the type object is INCREF’ed when a new instance is created, and DECREF’ed when an instance is destroyed (this does not apply to instances of subtypes; only the type referenced by the instance’s ob_type gets INCREF’ed or DECREF’ed). Heap types should also
as they can form a reference cycle with their own module object.
Inheritance:
???
Py_TPFLAGS_BASETYPE
Part of the
.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
.
Inheritance:
???
Py_TPFLAGS_READYING
This bit is set while
is in the process of initializing the type object.
Inheritance:
???
Py_TPFLAGS_HAVE_GC
Part of the
.This bit is set when the object supports garbage collection. If this bit is set, memory for new instances (see
) must be allocated using
or
and deallocated (see
) using
. More information in section
Supporting Cyclic Garbage Collection
.
Inheritance:
Group:
,
,
The
flag bit is inherited together with the
and
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
Part of the
.This is a bitmask of all the bits that pertain to the existence of certain fields in the type object and its extension structures. Currently, it includes the following bits:
Py_TPFLAGS_HAVE_STACKLESS_EXTENSION
.
Inheritance:
???
Py_TPFLAGS_METHOD_DESCRIPTOR
Part of the
since version 3.8.This bit indicates that objects behave like unbound methods.
If this flag is set for type(meth), then:
meth.__get__(obj,cls)(*args,**kwds) (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.
Added in version 3.8.
Inheritance:
This flag is never inherited by types without the
flag set. For extension types, it is inherited whenever
is inherited.
Py_TPFLAGS_MANAGED_DICT
This bit indicates that instances of the class have a
attribute, and that the space for the dictionary is managed by the VM.
If this flag is set,
must also be set.
The type traverse function must call
and its clear function must call
.
Added in version 3.12.
Inheritance:
This flag is inherited unless the
field is set in a superclass.
Py_TPFLAGS_MANAGED_WEAKREF
This bit indicates that instances of the class should be weakly referenceable.
If this flag is set,
must also be set.
Added in version 3.12.
Inheritance:
This flag is inherited unless the
field is set in a superclass.
These bits indicate that the VM will manage some fields by storing them before the object. Currently, this macro is equivalent to
|
.
This macro value relies on the implementation of the VM, so its value is not stable and may change in a future version. Prefer using individual flags instead.
Added in version 3.12.
Py_TPFLAGS_ITEMS_AT_END
Part of the
since version 3.12.Only usable with variable-size types, i.e. ones with non-zero
.
Indicates that the variable-sized portion of an instance of this type is at the end of the instance’s memory area, at an offset of Py_TYPE(obj)->tp_basicsize (which may be different in each subclass).
When setting this flag, be sure that all superclasses either use this memory layout, or are not variable-sized. Python does not check this.
Added in version 3.12.
Inheritance:
This flag is inherited.
Py_TPFLAGS_LONG_SUBCLASS
Py_TPFLAGS_LIST_SUBCLASS
Py_TPFLAGS_TUPLE_SUBCLASS
Py_TPFLAGS_BYTES_SUBCLASS
Py_TPFLAGS_UNICODE_SUBCLASS
Py_TPFLAGS_DICT_SUBCLASS
Py_TPFLAGS_BASE_EXC_SUBCLASS
Py_TPFLAGS_TYPE_SUBCLASS
Functions such as
will call
with one of these flags to quickly determine if a type is a subclass of a built-in type; such specific checks are faster than a generic check, like
. Custom types that inherit from built-ins should have their
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
slot is present in the type structure.
Added in version 3.4.
Deprecated since version 3.8: This flag isn’t necessary anymore, as the interpreter assumes the
slot is always present in the type structure.
Py_TPFLAGS_HAVE_VECTORCALL
Part of the
since version 3.12.This bit is set when the class implements the
. See
for details.
Inheritance:
This bit is inherited if
is also inherited.
Added in version 3.8: as _Py_TPFLAGS_HAVE_VECTORCALL
Changed in version 3.9: Renamed to the current name, without the leading underscore. The old provisional name is
.
Changed in version 3.12: This flag is now removed from a class when the class’s
method is reassigned.
This flag can now be inherited by mutable classes.
Py_TPFLAGS_IMMUTABLETYPE
This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.
automatically applies this flag to
.
Inheritance:
This flag is not inherited.
Added in version 3.10.
Py_TPFLAGS_DISALLOW_INSTANTIATION
Disallow creating instances of the type: set
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
is called on the type.
The flag is set automatically on
if
is NULL or &PyBaseObject_Type and
is NULL.
Inheritance:
This flag is not inherited. However, subclasses will not be instantiable unless they provide a non-NULL
(which is only possible via the C API).
Note
To disallow instantiating a class directly but allow instantiating its subclasses (e.g. for an
), do not use this flag. Instead, make
only succeed for subclasses.
Added in version 3.10.
Py_TPFLAGS_MAPPING
This bit indicates that instances of the class may match mapping patterns when used as the subject of a
block. It is automatically set when registering or subclassing
, and unset when registering
.
Note
and
are mutually exclusive; it is an error to enable both flags simultaneously.
Inheritance:
This flag is inherited by types that do not already set
.
See also
– Structural Pattern Matching: Specification
Added in version 3.10.
Py_TPFLAGS_SEQUENCE
This bit indicates that instances of the class may match sequence patterns when used as the subject of a
block. It is automatically set when registering or subclassing
, and unset when registering
.
Note
and
are mutually exclusive; it is an error to enable both flags simultaneously.
Inheritance:
This flag is inherited by types that do not already set
.
See also
– Structural Pattern Matching: Specification
Added in version 3.10.
Py_TPFLAGS_VALID_VERSION_TAG
Internal. Do not set or unset this flag. To indicate that a class has changed call
Warning
This flag is present in header files, but is not be used. It will be removed in a future version of CPython
Py_TPFLAGS_HAVE_VERSION_TAG
This macro does nothing. Historically, this would indicate that the
field was available and initialized.
Py_TPFLAGS_INLINE_VALUES
This bit indicates that instances of this type will have an “inline values” array (containing the object’s attributes) placed directly after the end of the object.
This requires that
is set.
Inheritance:
This flag is not inherited.
Added in version 3.13.
Py_TPFLAGS_IS_ABSTRACT
This bit indicates that this is an abstract type and therefore cannot be instantiated.
Inheritance:
This flag is not inherited.
Py_TPFLAGS_HAVE_STACKLESS_EXTENSION
Internal. Do not set or unset this flag. Historically, this was a reserved flag for use in Stackless Python.
Warning
This flag is present in header files, but is not be used. This may be removed in a future version of CPython.
constchar*
.tp_doc
The corresponding
Py_tp_doc is part of the
.
An optional pointer to a NUL-terminated C string giving the docstring for this type object. This is exposed as the
attribute on the type and instances of the type.
Inheritance:
This field is not inherited by subtypes.
.tp_traverse
The corresponding
Py_tp_traverse is part of the
.
An optional pointer to a traversal function for the garbage collector. This is only used if the
flag bit is set.
See
for documentation.
Inheritance:
Group:
,
,
This field is inherited by subtypes together with
and the
flag bit: the flag bit,
, and tp_clear are all inherited from the base type if they are all zero in the subtype.
.tp_clear
The corresponding
Py_tp_clear is part of the
.
An optional pointer to a clear function. The signature is:
inttp_clear(PyObject*);The purpose of this function is to break reference cycles that are causing a
so that the objects can be safely destroyed. A cleared object is a partially destroyed object; the object is not obligated to satisfy design invariants held during normal use.
tp_clear does not need to delete references to objects that can’t participate in reference cycles, such as Python strings or Python integers. However, it may be convenient to clear all references, and write the type’s
function to invoke tp_clear to avoid code duplication. (Beware that tp_clear might have already been called. Prefer calling idempotent functions like
.)
Any non-trivial cleanup should be performed in
instead of tp_clear.
Note
If tp_clear fails to break a reference cycle then the objects in the
may remain indefinitely uncollectable (“leak”). See
.
Note
Referents (direct and indirect) might have already been cleared; they are not guaranteed to be in a consistent state.
Note
The
function can be called from any thread.
Note
An object is not guaranteed to be automatically cleared before its destructor (
) is called.
This function differs from the destructor (
) in the following ways:
The purpose of clearing an object is to remove references to other objects that might participate in a reference cycle. The purpose of the destructor, on the other hand, is a superset: it must release all resources it owns, including references to objects that cannot participate in a reference cycle (e.g., integers) as well as the object’s own memory (by calling
).
When tp_clear is called, other objects might still hold references to the object being cleared. Because of this, tp_clear must not deallocate the object’s own memory (
). The destructor, on the other hand, is only called when no (strong) references exist, and as such, must safely destroy the object itself by deallocating it.
tp_clear might never be automatically called. An object’s destructor, on the other hand, will be automatically called some time after the object becomes unreachable (i.e., either there are no references to the object or the object is a member of a
).
No guarantees are made about when, if, or how often Python automatically clears an object, except:
Python will not automatically clear an object if it is reachable, i.e., there is a reference to it and it is not a member of a
.
Python will not automatically clear an object if it has not been automatically finalized (see
). (If the finalizer resurrected the object, the object may or may not be automatically finalized again before it is cleared.)
If an object is a member of a
, Python will not automatically clear it if any member of the cyclic isolate has not yet been automatically finalized (
).
Python will not destroy an object until after any automatic calls to its tp_clear function have returned. This ensures that the act of breaking a reference cycle does not invalidate the self pointer while tp_clear is still executing.
Python will not automatically call tp_clear multiple times concurrently.
CPython currently only automatically clears objects as needed to break reference cycles in a
, but future versions might clear objects regularly before their destruction.
Taken together, all
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 are responsible for breaking any cycle containing a tuple. This isn’t immediately obvious, and there’s rarely a good reason to avoid implementing tp_clear.
Implementations of
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:
staticintlocal_clear(PyObject*op){localobject*self=(localobject*)op;Py_CLEAR(self->key);Py_CLEAR(self->args);Py_CLEAR(self->kw);Py_CLEAR(self->dict);return0;}The
macro should be used, because clearing references is delicate: the reference to the contained object must not be released (via
) until after the pointer to the contained object is set to NULL. This is because releasing the reference may cause the contained object to become trash, triggering a chain of reclamation activity that may include invoking arbitrary Python code (due to finalizers, or weakref callbacks, associated with the contained object). If it’s possible for such code to reference self again, it’s important that the pointer to the contained object be NULL at that time, so that self knows the contained object can no longer be used. The Py_CLEAR() macro performs the operations in a safe order.
If the
bit is set in the
field, the clear function must call
like this:
PyObject_ClearManagedDict((PyObject*)self);More information about Python’s garbage collection scheme can be found in section
Supporting Cyclic Garbage Collection
.
Inheritance:
Group:
,
,
This field is inherited by subtypes together with
and the
flag bit: the flag bit, tp_traverse, and
are all inherited from the base type if they are all zero in the subtype.
.tp_richcompare
The corresponding
Py_tp_richcompare is part of the
.
An optional pointer to the rich comparison function, whose signature is:
PyObject*tp_richcompare(PyObject*self,PyObject*other,intop);The first parameter is guaranteed to be an instance of the type that is defined by
.
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
and for
:
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 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
.
The returned value is a new
.
On error, sets an exception and returns NULL from the function.
Added in version 3.7.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits
and tp_hash when the subtype’s tp_richcompare and tp_hash are both NULL.
Default:
provides a
implementation, which may be inherited. However, if only
is defined, not even the inherited function is used and instances of the type will not be able to participate in any comparisons.
.tp_weaklistoffset
While this field is still supported,
should be used instead, if at all possible.
If the instances of this type are weakly referenceable, this field is greater than zero and contains the offset in the instance structure of the weak reference list head (ignoring the GC header, if present); this offset is used by
and the PyWeakref_* functions. The instance structure needs to include a field of type
* which is initialized to NULL.
Do not confuse this field with
; that is the list head for weak references to the type object itself.
It is an error to set both the
bit and
.
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
, this should not be a problem.
Default:
If the
bit is set in the
field, then
will be set to a negative value, to indicate that it is unsafe to use this field.
.tp_iter
The corresponding
Py_tp_iter is part of the
.
An optional pointer to a function that returns an
for the object. Its presence normally signals that the instances of this type are
(although sequences may be iterable without this function).
This function has the same signature as
:
PyObject*tp_iter(PyObject*self);Inheritance:
This field is inherited by subtypes.
.tp_iternext
The corresponding
Py_tp_iternext is part of the
.
An optional pointer to a function that returns the next item in an
. The signature is:
PyObject*tp_iternext(PyObject*self);When the iterator is exhausted, it must return NULL; a
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
function, and that function should return the iterator instance itself (not a new iterator instance).
This function has the same signature as
.
Inheritance:
This field is inherited by subtypes.
struct
*
.tp_methods
The corresponding
Py_tp_methods is part of the
.
An optional pointer to a static NULL-terminated array of
structures, declaring regular methods of this type.
For each entry in the array, an entry is added to the type’s dictionary (see
below) containing a method descriptor.
Inheritance:
This field is not inherited by subtypes (methods are inherited through a different mechanism).
struct
*
.tp_members
The corresponding
Py_tp_members is part of the
.
An optional pointer to a static NULL-terminated array of
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
below) containing a member descriptor.
Inheritance:
This field is not inherited by subtypes (members are inherited through a different mechanism).
struct
*
.tp_getset
The corresponding
Py_tp_getset is part of the
.
An optional pointer to a static NULL-terminated array of
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
below) containing a getset descriptor.
Inheritance:
This field is not inherited by subtypes (computed attributes are inherited through a different mechanism).
*
.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.
For the corresponding slot ID, see
.
Note
Slot initialization is subject to the rules of initializing globals. C99 requires the initializers to be “address constants”. Function designators like
, with implicit conversion to a pointer, are valid C99 address constants.
However, the unary ‘&’ operator applied to a non-static variable like
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,
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
).
*
.tp_dict
The type’s dictionary is stored here by
.
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
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
). Once initialization for the type has finished, this field should be treated as read-only.
Some types may not store their dictionary in this slot. Use
to retrieve the dictionary for an arbitrary type.
Changed in version 3.12: Internals detail: For static builtin types, this is always NULL. Instead, the dict for such types is stored on PyInterpreterState. Use
to get the dict for an arbitrary type.
Inheritance:
This field is not inherited by subtypes (though the attributes defined in here are inherited through a different mechanism).
Default:
If this field is NULL,
will assign a new dictionary to it.
Warning
It is not safe to use
on or otherwise modify
with the dictionary C-API.
.tp_descr_get
The corresponding
Py_tp_descr_get is part of the
.
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.
.tp_descr_set
The corresponding
Py_tp_descr_set is part of the
.
An optional pointer to a function for setting and deleting a descriptor’s value.
The function signature is:
inttp_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.
.tp_dictoffset
While this field is still supported,
should be used instead, if at all possible.
If the instances of this type have a dictionary containing instance variables, this field is non-zero and contains the offset in the instances of the type of the instance variable dictionary; this offset is used by
.
Do not confuse this field with
; that is the dictionary for attributes of the type object itself.
The value specifies the offset of the dictionary from the start of the instance structure.
The
should be regarded as write-only. To get the pointer to the dictionary call
. Calling PyObject_GenericGetDict() may need to allocate memory for the dictionary, so it is may be more efficient to call
when accessing an attribute on the object.
It is an error to set both the
bit and
.
Inheritance:
This field is inherited by subtypes. A subtype should not override this offset; doing so could be unsafe, if C code tries to access the dictionary at the previous offset. To properly support inheritance, use
.
Default:
This slot has no default. For
, if the field is NULL then no
gets created for instances.
If the
bit is set in the
field, then
will be set to -1, to indicate that it is unsafe to use this field.
.tp_init
The corresponding
Py_tp_init is part of the
.
An optional pointer to an instance initialization function.
This function corresponds to the
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:
inttp_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
.
The
function, if not NULL, is called when an instance is created normally by calling its type, after the type’s
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
this field does not have a default.
.tp_alloc
The corresponding
Py_tp_alloc is part of the
.
An optional pointer to an instance allocation function.
The function signature is:
PyObject*tp_alloc(PyTypeObject*self,Py_ssize_tnitems);Inheritance:
Static subtypes inherit this slot, which will be
if inherited from
.
do not inherit this slot.
Default:
For heap subtypes, this field is always set to
.
For static subtypes, this slot is inherited (see above).
.tp_new
The corresponding
Py_tp_new is part of the
.
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
function is called; it may be a subtype of that type (but not an unrelated type).
The
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
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.
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
whose
is NULL or &PyBaseObject_Type.
Default:
For
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.
.tp_free
The corresponding
Py_tp_free is part of the
.
An optional pointer to an instance deallocation function. Its signature is:
voidtp_free(void*self);This function must free the memory allocated by
.
Inheritance:
Static subtypes inherit this slot, which will be
if inherited from
. Exception: If the type supports garbage collection (i.e., the
flag is set in
) and it would inherit PyObject_Free(), then this slot is not inherited but instead defaults to
.
do not inherit this slot.
Default:
For
, this slot defaults to a deallocator suitable to match
and the value of the
flag.
For static subtypes, this slot is inherited (see above).
.tp_is_gc
The corresponding
Py_tp_is_gc is part of the
.
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
field, and check the
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:
inttp_is_gc(PyObject*self);(The only example of this are types themselves. The metatype,
, defines this function to distinguish between statically and
.)
Inheritance:
This field is inherited by subtypes.
Default:
This slot has no default. If this field is NULL,
is used as the functional equivalent.
*
.tp_bases
Tuple of base types.
This field should be set to NULL and treated as read-only. Python will fill it in when the type is
.
For the corresponding slot ID, see
.
Warning
Multiple inheritance does not work well for statically defined types. If you set tp_bases to a tuple, Python will not raise an error, but some slots will only be inherited from the first base.
Inheritance:
This field is not inherited.
*
.tp_mro
Tuple containing the expanded set of base types, starting with the type itself and ending with
, in Method Resolution Order.
This field should be set to NULL and treated as read-only. Python will fill it in when the type is
.
Inheritance:
This field is not inherited; it is calculated fresh by
.
*
.tp_cache
Unused. Internal use only.
Inheritance:
This field is not inherited.
void*
.tp_subclasses
A collection of subclasses. Internal use only. May be an invalid pointer.
To get a list of subclasses, call the Python method
.
Changed in version 3.12: For some types, this field does not hold a valid
*. The type was changed to void* to indicate this.
Inheritance:
This field is not inherited.
*
.tp_weaklist
Weak reference list head, for weak references to this type object. Not inherited. Internal use only.
Changed in version 3.12: Internals detail: For the static builtin types this is always NULL, even if weakrefs are added. Instead, the weakrefs for each are stored on PyInterpreterState. Use the public C-API or the internal _PyObject_GET_WEAKREFS_LISTPTR() macro to avoid the distinction.
Inheritance:
This field is not inherited.
.tp_del
The corresponding
Py_tp_del is part of the
.
This field is deprecated. Use
instead.
unsignedint
.tp_version_tag
Used to index into the method cache. Internal use only.
Inheritance:
This field is not inherited.
.tp_finalize
The corresponding
Py_tp_finalize is part of the
since version 3.5.
An optional pointer to an instance finalization function. This is the C implementation of the
special method. Its signature is:
voidtp_finalize(PyObject*self);The primary purpose of finalization is to perform any non-trivial cleanup that must be performed before the object is destroyed, while the object and any other objects it directly or indirectly references are still in a consistent state. The finalizer is allowed to execute arbitrary Python code.
Before Python automatically finalizes an object, some of the object’s direct or indirect referents might have themselves been automatically finalized. However, none of the referents will have been automatically cleared (
) yet.
Other non-finalized objects might still be using a finalized object, so the finalizer must leave the object in a sane state (e.g., invariants are still met).
Note
After Python automatically finalizes an object, Python might start automatically clearing (
) the object and its referents (direct and indirect). Cleared objects are not guaranteed to be in a consistent state; a finalized object must be able to tolerate cleared referents.
Note
An object is not guaranteed to be automatically finalized before its destructor (
) is called. It is recommended to call
PyObject_CallFinalizerFromDealloc()
at the beginning of tp_dealloc to guarantee that the object is always finalized before destruction.
Note
The
function can be called from any thread, although the
will be held.
Note
The tp_finalize function can be called during shutdown, after some global variables have been deleted. See the documentation of the
method for details.
When Python finalizes an object, it behaves like the following algorithm:
Python might mark the object as finalized. Currently, Python always marks objects whose type supports garbage collection (i.e., the
flag is set in
) and never marks other types of objects; this might change in a future version.
If the object is not marked as finalized and its tp_finalize finalizer function is non-NULL, the finalizer function is called.
If the finalizer function was called and the finalizer made the object reachable (i.e., there is a reference to the object and it is not a member of a
), then the finalizer is said to have resurrected the object. It is unspecified whether the finalizer can also resurrect the object by adding a new reference to the object that does not make it reachable, i.e., the object is (still) a member of a cyclic isolate.
If the finalizer resurrected the object, the object’s pending destruction is canceled and the object’s finalized mark might be removed if present. Currently, Python never removes the finalized mark; this might change in a future version.
Automatic finalization refers to any finalization performed by Python except via calls to
or
PyObject_CallFinalizerFromDealloc()
. No guarantees are made about when, if, or how often an object is automatically finalized, except:
Python will not automatically finalize an object if it is reachable, i.e., there is a reference to it and it is not a member of a
.
Python will not automatically finalize an object if finalizing it would not mark the object as finalized. Currently, this applies to objects whose type does not support garbage collection, i.e., the
flag is not set. Such objects can still be manually finalized by calling
or
PyObject_CallFinalizerFromDealloc()
.
Python will not automatically finalize any two members of a
concurrently.
Python will not automatically finalize an object after it has automatically cleared (
) the object.
If an object is a member of a
, Python will not automatically finalize it after automatically clearing (see
) any other member.
Python will automatically finalize every member of a
before it automatically clears (see
) any of them.
If Python is going to automatically clear an object (
), it will automatically finalize the object first.
Python currently only automatically finalizes objects that are members of a
, but future versions might finalize objects regularly before their destruction.
To manually finalize an object, do not call this function directly; call
or
PyObject_CallFinalizerFromDealloc()
instead.
should leave the current exception status unchanged. The recommended way to write a non-trivial finalizer is to back up the exception at the beginning by calling
and restore the exception at the end by calling
. If an exception is encountered in the middle of the finalizer, log and clear it with
or
. For example:
staticvoidfoo_finalize(PyObject*self){// Save the current exception, if any.PyObject*exc=PyErr_GetRaisedException();// ...if(do_something_that_might_raise()!=success_indicator){PyErr_WriteUnraisable(self);gotodone;}done:// Restore the saved exception. This silently discards any exception// raised above, so be sure to call PyErr_WriteUnraisable first if// necessary.PyErr_SetRaisedException(exc);}Inheritance:
This field is inherited by subtypes.
Added in version 3.4.
Changed in version 3.8: Before version 3.8 it was necessary to set the
flags bit in order for this field to be used. This is no longer required.
See also
: “Safe object finalization”
for details about how this slot relates to other slots.
PyObject_CallFinalizerFromDealloc()
.tp_vectorcall
The corresponding
Py_tp_vectorcall is part of the
since version 3.14.
A
to use for calls of this type object (rather than instances). In other words, tp_vectorcall can be used to optimize type.__call__, which typically returns a new instance of type.
As with any vectorcall function, if tp_vectorcall is NULL, the tp_call protocol (Py_TYPE(type)->tp_call) is used instead.
Note
The
requires that the vectorcall function has the same behavior as the corresponding tp_call. This means that type->tp_vectorcall must match the behavior of Py_TYPE(type)->tp_call.
Specifically, if type uses the default metaclass, type->tp_vectorcall must behave the same as
->tp_call, which:
calls type->tp_new,
if the result is a subclass of type, calls type->tp_init on the result of tp_new, and
returns the result of tp_new.
Typically, tp_vectorcall is overridden to optimize this process for specific
and
. When doing this for user-subclassable types, note that both can be overridden (using
and
, respectively).
Inheritance:
This field is never inherited.
Added in version 3.9: (the field exists since 3.8 but it’s only used since 3.9)
unsignedchar
.tp_watched
Internal. Do not use.
Added in version 3.12.
Static Types
Traditionally, types defined in C code are static, that is, a static
structure is defined directly in code and initialized using
.
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
, so they should not include any subinterpreter-specific state.
Also, since
is only part of the
as an opaque struct, any extension modules using static types must be compiled for a specific Python minor version.
Heap Types
An alternative to
is heap-allocated types, or heap types for short, which correspond closely to classes created by Python’s class statement. Heap types have the
flag set.
This is done by filling a
structure and calling
,
,
, or
.
Number Object Structures
typePyNumberMethods
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
section.
Here is the structure definition:
typedefstruct{binaryfuncnb_add;binaryfuncnb_subtract;binaryfuncnb_multiply;binaryfuncnb_remainder;binaryfuncnb_divmod;ternaryfuncnb_power;unaryfuncnb_negative;unaryfuncnb_positive;unaryfuncnb_absolute;inquirynb_bool;unaryfuncnb_invert;binaryfuncnb_lshift;binaryfuncnb_rshift;binaryfuncnb_and;binaryfuncnb_xor;binaryfuncnb_or;unaryfuncnb_int;void*nb_reserved;unaryfuncnb_float;binaryfuncnb_inplace_add;binaryfuncnb_inplace_subtract;binaryfuncnb_inplace_multiply;binaryfuncnb_inplace_remainder;ternaryfuncnb_inplace_power;binaryfuncnb_inplace_lshift;binaryfuncnb_inplace_rshift;binaryfuncnb_inplace_and;binaryfuncnb_inplace_xor;binaryfuncnb_inplace_or;binaryfuncnb_floor_divide;binaryfuncnb_true_divide;binaryfuncnb_inplace_floor_divide;binaryfuncnb_inplace_true_divide;unaryfuncnb_index;binaryfuncnb_matrix_multiply;binaryfuncnb_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
field should always be NULL. It was previously called nb_long, and was renamed in Python 3.0.1.
.nb_add
The corresponding
Py_nb_add is part of the
.
.nb_subtract
The corresponding
Py_nb_subtract is part of the
.
.nb_multiply
The corresponding
Py_nb_multiply is part of the
.
.nb_remainder
The corresponding
Py_nb_remainder is part of the
.
.nb_divmod
The corresponding
Py_nb_divmod is part of the
.
.nb_power
The corresponding
Py_nb_power is part of the
.
.nb_negative
The corresponding
Py_nb_negative is part of the
.
.nb_positive
The corresponding
Py_nb_positive is part of the
.
.nb_absolute
The corresponding
Py_nb_absolute is part of the
.
.nb_bool
The corresponding
Py_nb_bool is part of the
.
.nb_invert
The corresponding
Py_nb_invert is part of the
.
.nb_lshift
The corresponding
Py_nb_lshift is part of the
.
.nb_rshift
The corresponding
Py_nb_rshift is part of the
.
.nb_and
The corresponding
Py_nb_and is part of the
.
.nb_xor
The corresponding
Py_nb_xor is part of the
.
.nb_or
The corresponding
Py_nb_or is part of the
.
.nb_int
The corresponding
Py_nb_int is part of the
.
void*
.nb_reserved
.nb_float
The corresponding
Py_nb_float is part of the
.
.nb_inplace_add
The corresponding
Py_nb_inplace_add is part of the
.
.nb_inplace_subtract
The corresponding
Py_nb_inplace_subtract is part of the
.
.nb_inplace_multiply
The corresponding
Py_nb_inplace_multiply is part of the
.
.nb_inplace_remainder
The corresponding
Py_nb_inplace_remainder is part of the
.
.nb_inplace_power
The corresponding
Py_nb_inplace_power is part of the
.
.nb_inplace_lshift
The corresponding
Py_nb_inplace_lshift is part of the
.
.nb_inplace_rshift
The corresponding
Py_nb_inplace_rshift is part of the
.
.nb_inplace_and
The corresponding
Py_nb_inplace_and is part of the
.
.nb_inplace_xor
The corresponding
Py_nb_inplace_xor is part of the
.
.nb_inplace_or
The corresponding
Py_nb_inplace_or is part of the
.
.nb_floor_divide
The corresponding
Py_nb_floor_divide is part of the
.
.nb_true_divide
The corresponding
Py_nb_true_divide is part of the
.
.nb_inplace_floor_divide
The corresponding
Py_nb_inplace_floor_divide is part of the
.
.nb_inplace_true_divide
The corresponding
Py_nb_inplace_true_divide is part of the
.
.nb_index
The corresponding
Py_nb_index is part of the
.
.nb_matrix_multiply
The corresponding
Py_nb_matrix_multiply is part of the
since version 3.5.
.nb_inplace_matrix_multiply
The corresponding
Py_nb_inplace_matrix_multiply is part of the
since version 3.5.
Mapping Object Structures
typePyMappingMethods
This structure holds pointers to the functions which an object uses to implement the mapping protocol. It has three members:
.mp_length
The corresponding
Py_mp_length is part of the
.
This function is used by
and
, and has the same signature. This slot may be set to NULL if the object has no defined length.
.mp_subscript
The corresponding
Py_mp_subscript is part of the
.
This function is used by
and
, and has the same signature as PyObject_GetItem(). This slot must be filled for the
function to return 1, it can be NULL otherwise.
.mp_ass_subscript
The corresponding
Py_mp_ass_subscript is part of the
.
This function is used by
,
,
and
. It has the same signature as PyObject_SetItem(), but v can also be set to NULL to delete an item. If this slot is NULL, the object does not support item assignment and deletion.
Sequence Object Structures
typePySequenceMethods
This structure holds pointers to the functions which an object uses to implement the sequence protocol.
.sq_length
The corresponding
Py_sq_length is part of the
.
This function is used by
and
, and has the same signature. It is also used for handling negative indices via the
and the
slots.
.sq_concat
The corresponding
Py_sq_concat is part of the
.
This function is used by
and has the same signature. It is also used by the + operator, after trying the numeric addition via the
slot.
.sq_repeat
The corresponding
Py_sq_repeat is part of the
.
This function is used by
and has the same signature. It is also used by the * operator, after trying numeric multiplication via the
slot.
.sq_item
The corresponding
Py_sq_item is part of the
.
This function is used by
and has the same signature. It is also used by
, after trying the subscription via the
slot. This slot must be filled for the
function to return 1, it can be NULL otherwise.
Negative indexes are handled as follows: if the
slot is filled, it is called and the sequence length is used to compute a positive index which is passed to
. If sq_length is NULL, the index is passed as is to the function.
.sq_ass_item
The corresponding
Py_sq_ass_item is part of the
.
This function is used by
and has the same signature. It is also used by
and
, after trying the item assignment and deletion via the
slot. This slot may be left to NULL if the object does not support item assignment and deletion.
.sq_contains
The corresponding
Py_sq_contains is part of the
.
This function may be used by
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.
.sq_inplace_concat
The corresponding
Py_sq_inplace_concat is part of the
.
This function is used by
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
. It is also used by the augmented assignment +=, after trying numeric in-place addition via the
slot.
.sq_inplace_repeat
The corresponding
Py_sq_inplace_repeat is part of the
.
This function is used by
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
. It is also used by the augmented assignment *=, after trying numeric in-place multiplication via the
slot.
Buffer Object Structures
typePyBufferProcs
This structure holds pointers to the functions required by the
. The protocol defines how an exporter object can expose its internal data to consumer objects.
.bf_getbuffer
The corresponding
Py_bf_getbuffer is part of the
since version 3.11.
The signature of this function is:
int(PyObject*exporter,Py_buffer*view,intflags);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
, 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.
Thread safety:
In the
, implementations must ensure:
The export counter increment in step (3) is atomic.
The underlying buffer data remains valid and at a stable memory location for the lifetime of all exports.
For objects that support resizing or reallocation (such as
), the export counter is checked atomically before such operations, and
is raised if exports exist.
The function is safe to call concurrently from multiple threads.
See also
Thread safety for memoryview objects
for the Python-level thread safety guarantees of
objects.
If exporter is part of a chain or tree of buffer providers, two main schemes can be used:
Re-export: Each member of the tree acts as the exporting object and sets view->obj to a new reference to itself.
Redirect: The buffer request is redirected to the root object of the tree. Here, view->obj will be a new reference to the root object.
The individual fields of view are described in section
, the rules how an exporter must react to specific requests are in section
.
All memory pointed to in the
structure belongs to the exporter and must remain valid until there are no consumers left.
,
,
,
and
are read-only for the consumer.
provides an easy way of exposing a simple bytes buffer while dealing correctly with all request types.
is the interface for the consumer that wraps this function.
.bf_releasebuffer
The corresponding
Py_bf_releasebuffer is part of the
since version 3.11.
The signature of this function is:
void(PyObject*exporter,Py_buffer*view);Handle a request to release the resources of the buffer. If no resources need to be released,
PyBufferProcs.bf_releasebuffer
may 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.
Thread safety:
In the
:
The export counter decrement in step (1) must be atomic.
Resource cleanup when the counter reaches zero must be done atomically, as the final release may race with concurrent releases from other threads and deallocation must only happen once.
The exporter MUST use the
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
(this scheme is useful for breaking reference cycles).
is the interface for the consumer that wraps this function.
Async Object Structures
Added in version 3.5.
typePyAsyncMethods
This structure holds pointers to the functions required to implement
and
objects.
Here is the structure definition:
typedefstruct{unaryfuncam_await;unaryfuncam_aiter;unaryfuncam_anext;sendfuncam_send;}PyAsyncMethods;
.am_await
The corresponding
Py_am_await is part of the
since version 3.5.
The signature of this function is:
PyObject*am_await(PyObject*self);The returned object must be an
, i.e.
must return 1 for it.
This slot may be set to NULL if an object is not an
.
.am_aiter
The corresponding
Py_am_aiter is part of the
since version 3.5.
The signature of this function is:
PyObject*am_aiter(PyObject*self);Must return an
object. See
for details.
This slot may be set to NULL if an object does not implement asynchronous iteration protocol.
.am_anext
The corresponding
Py_am_anext is part of the
since version 3.5.
The signature of this function is:
PyObject*am_anext(PyObject*self);Must return an
object. See
for details. This slot may be set to NULL.
.am_send
The corresponding
Py_am_send is part of the
since version 3.10.
The signature of this function is:
PySendResultam_send(PyObject*self,PyObject*arg,PyObject**result);See
for details. This slot may be set to NULL.
Added in version 3.10.
Slot Type typedefs
typedef
*(*allocfunc)(
*cls,
nitems)
Part of the
.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
set to 1 and
set to the type argument. If the type’s
is non-zero, the object’s
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
.
This function should not do any other instance initialization, not even to allocate additional memory; that should be done by
.
typedefvoid(*destructor)(
*)
Part of the
.typedefvoid(*freefunc)(void*)
See
.
typedef
*(*newfunc)(
*,
*,
*)
Part of the
.See
.
typedefint(*initproc)(
*,
*,
*)
Part of the
.See
.
typedef
*(*reprfunc)(
*)
Part of the
.See
.
typedef
*(*getattrfunc)(
*self,char*attr)
Part of the
.Return the value of the named attribute for the object.
typedefint(*setattrfunc)(
*self,char*attr,
*value)
Part of the
.Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.
typedef
*(*getattrofunc)(
*self,
*attr)
Part of the
.Return the value of the named attribute for the object.
See
.
typedefint(*setattrofunc)(
*self,
*attr,
*value)
Part of the
.Set the value of the named attribute for the object. The value argument is set to NULL to delete the attribute.
See
.
typedef
*(*descrgetfunc)(
*,
*,
*)
Part of the
.See
.
typedefint(*descrsetfunc)(
*,
*,
*)
Part of the
.See
.
typedef
(*hashfunc)(
*)
Part of the
.See
.
typedef
*(*richcmpfunc)(
*,
*,int)
Part of the
.See
.
typedef
*(*getiterfunc)(
*)
Part of the
.See
.
typedef
*(*iternextfunc)(
*)
Part of the
.See
.
typedef
(*lenfunc)(
*)
Part of the
.typedefint(*getbufferproc)(
*,
*,int)
Part of the
since version 3.12.typedefvoid(*releasebufferproc)(
*,
*)
Part of the
since version 3.12.typedef
*(*unaryfunc)(
*)
Part of the
.typedef
*(*binaryfunc)(
*,
*)
Part of the
.typedef
(*sendfunc)(
*,
*,
**)
See
.
typedef
*(*ternaryfunc)(
*,
*,
*)
Part of the
.typedef
*(*ssizeargfunc)(
*,
)
Part of the
.typedefint(*ssizeobjargproc)(
*,
,
*)
Part of the
.typedefint(*objobjproc)(
*,
*)
Part of the
.typedefint(*objobjargproc)(
*,
*,
*)
Part of the
.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
:
typedefstruct{PyObject_HEADconstchar*data;}MyObject;staticPyTypeObjectMyObject_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:
staticPyTypeObjectMyObject_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:
typedefstruct{PyObject_HEADconstchar*data;}MyObject;staticPyTypeObjectMyObject_Type={PyVarObject_HEAD_INIT(NULL,0).tp_name="mymod.MyObject",.tp_basicsize=sizeof(MyObject),.tp_doc=PyDoc_STR("My objects"),.tp_flags=Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE|Py_TPFLAGS_HAVE_GC|Py_TPFLAGS_MANAGED_DICT|Py_TPFLAGS_MANAGED_WEAKREF,.tp_new=myobj_new,.tp_traverse=(traverseproc)myobj_traverse,.tp_clear=(inquiry)myobj_clear,.tp_alloc=PyType_GenericNew,.tp_dealloc=(destructor)myobj_dealloc,.tp_repr=(reprfunc)myobj_repr,.tp_hash=(hashfunc)myobj_hash,.tp_richcompare=PyBaseObject_Type.tp_richcompare,};A str subclass that cannot be subclassed and cannot be called to create instances (e.g. uses a separate factory func) using
Py_TPFLAGS_DISALLOW_INSTANTIATION
flag:
typedefstruct{PyUnicodeObjectraw;char*extra;}MyStr;staticPyTypeObjectMyStr_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
with fixed-length instances:
typedefstruct{PyObject_HEAD}MyObject;staticPyTypeObjectMyObject_Type={PyVarObject_HEAD_INIT(NULL,0).tp_name="mymod.MyObject",};The simplest
with variable-length instances:
typedefstruct{PyObject_VAR_HEADconstchar*data[1];}MyObject;staticPyTypeObjectMyObject_Type={PyVarObject_HEAD_INIT(NULL,0).tp_name="mymod.MyObject",.tp_basicsize=sizeof(MyObject)-sizeof(char*),.tp_itemsize=sizeof(char*),};