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__
~
[
]
*
[
]
*
__subclasses__
[
]
*
(
)
[
]
unsigned int
__del__
X
sub-slots
Slot
special methods
__await__
__aiter__
__anext__
__add__ __radd__
__iadd__
__sub__ __rsub__
__isub__
__mul__ __rmul__
__imul__
__mod__ __rmod__
__imod__
__divmod__ __rdivmod__
__pow__ __rpow__
__ipow__
__neg__
__pos__
__abs__
__bool__
__invert__
__lshift__ __rlshift__
__ilshift__
__rshift__ __rrshift__
__irshift__
__and__ __rand__
__iand__
__xor__ __rxor__
__ixor__
__or__ __ror__
__ior__
__int__
void *
__float__
__floordiv__
__ifloordiv__
__truediv__
__itruediv__
__index__
__matmul__ __rmatmul__
__imatmul__
__len__
__getitem__
__setitem__, __delitem__
__len__
__add__
__mul__
__getitem__
__setitem__ __delitem__
__contains__
__iadd__
__imul__
slot typedefs
typedef
Parameter Types
Return Type
*
*
*
void
void *
void
*
void *
int
*
*
*
*
*
*
*
int
*
*
*
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/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 */structPyMethodDef*tp_methods;structPyMemberDef*tp_members;structPyGetSetDef*tp_getset;// Strong reference on a heap type, borrowed reference on a static typestruct_typeobject*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;PyObject*tp_subclasses;PyObject*tp_weaklist;destructortp_del;/* Type attribute cache version tag. Added in version 2.6 */unsignedinttp_version_tag;destructortp_finalize;vectorcallfunctp_vectorcall;}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
field.
.ob_refcnt
Part of the
.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
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.
*
.ob_type
Part of the
.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
field of the base class.
will not change this field if it is non-zero.
Inheritance:
This field is inherited by subtypes.
*
._ob_next
*
._ob_prev
These fields are only present when the macro Py_TRACE_REFS is defined (see the
configure --with-trace-refs option
).
Their initialization to NULL is taken care of by the PyObject_HEAD_INIT macro. For
, these fields always remain NULL. For
, these two fields are used to link the object into a doubly linked list of all live objects on the heap.
This could be used for various debugging purposes; currently the only uses are the sys.getobjects() function and to print the objects that are still alive at the end of a run when the environment variable
is set.
Inheritance:
These fields are not inherited by subtypes.
PyVarObject Slots
.ob_size
Part of the
.For
statically allocated type objects
, this should be initialized to zero. For
dynamically allocated type objects
, this field has a special internal meaning.
Inheritance:
This field is not inherited by subtypes.
PyTypeObject Slots
Each slot has a section describing inheritance. If
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
effectively act as defaults.)
constchar*
.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
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
attribute.
If no dot is present, the entire
field is made accessible as the
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
(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.
There are two kinds of types: types with fixed-length instances have a zero
field, types with variable-length instances have a non-zero
field. For a type with fixed-length instances, all instances have the same size, given in
.
For a type with variable-length instances, the instances must have an
field, and the instance size is
plus N times
, where N is the “length” of the object. The value of N is typically stored in the instance’s
field. There are exceptions: for example, ints use a negative
to indicate a negative number, and N is abs(ob_size) there. Also, the presence of an
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
field).
The basic size includes the fields in the instance declared by the macro
or
(whichever is used to declare the instance struct) and this in turn includes the
and
fields if they are present. This means that the only correct way to get an initializer for the
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
. Example: suppose a type implements an array of double.
is sizeof(double). It is the programmer’s responsibility that
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
, it is generally not safe to set
to a different non-zero value in a subtype (though this depends on the implementation of the base type).
.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:
voidtp_dealloc(PyObject*self);The destructor function is called by the
and
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
function. If the type is not subtypable (doesn’t have the
flag bit set), it is permissible to call the object deallocator directly instead of via
. The object deallocator should be the one used to allocate the instance; this is normally
if the instance was allocated using
or
, or
if the instance was allocated using
or
.
If the type supports garbage collection (has the
flag bit set), the destructor should call
before clearing any member fields.
staticvoidfoo_dealloc(foo_object*self){PyObject_GC_UnTrack(self);Py_CLEAR(self->ref);Py_TYPE(self)->tp_free((PyObject*)self);}Finally, if the type is heap allocated (
), the deallocator should release the owned reference to its type object (via
) after calling the type deallocator. In order to avoid dangling pointers, the recommended way to achieve this is:
staticvoidfoo_dealloc(foo_object*self){PyTypeObject*tp=Py_TYPE(self);// free references and buffers heretp->tp_free(self);Py_DECREF(tp);}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
.
Warning
It is not recommended for
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.
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
flag is not always inherited. If it’s not, then the subclass won’t use
, except when
is explicitly called. This is in particular the case for types without the
flag set (including subclasses defined in Python).
.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
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
from its base type when the subtype’s
and
are both NULL.
.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
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
from its base type when the subtype’s
and
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.
New 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
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
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
.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits both of
and
, when the subtype’s
and
are both NULL.
.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*tp_call(PyObject*self,PyObject*args,PyObject*kwargs);Inheritance:
This field is inherited by subtypes.
.tp_str
An optional pointer to a function that implements the built-in operation
. (Note that
is a type now, and
calls the constructor for that type. This constructor calls
to do the actual work, and
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
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
and
from its base type when the subtype’s
and
are both NULL.
Default:
PyBaseObject_Type uses
.
.tp_setattro
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
and
from its base type when the subtype’s
and
are both NULL.
Default:
PyBaseObject_Type 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
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
flag bit is clear in the subtype and the
and
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
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).
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
.
Inheritance:
???
Py_TPFLAGS_READYING
This bit is set while
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
and destroyed using
. More information in section
Supporting Cyclic Garbage Collection
. This bit also implies that the GC-related fields
and
are present in the type object.
Inheritance:
Group:
,
,
The
flag bit is inherited together with the
and
fields, i.e. if the
flag bit is clear in the subtype and the
and
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.
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 types without the
flag set. For extension types, it is inherited whenever
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
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.
New 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
This bit is set when the class implements the
. See
for details.
Inheritance:
This bit is inherited for types with the
flag set, if
is also inherited.
New in version 3.9.
Py_TPFLAGS_IMMUTABLETYPE
This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.
automatically applies this flag to
.
Inheritance:
This flag is not inherited.
New 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.
New in version 3.10.
Py_TPFLAGS_MAPPING
This bit indicates that instances of the class may match mapping patterns when used as the subject of a
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
New in version 3.10.
Py_TPFLAGS_SEQUENCE
This bit indicates that instances of the class may match sequence patterns when used as the subject of a
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
New in version 3.10.
constchar*
.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.
.tp_traverse
An optional pointer to a traversal function for the garbage collector. This is only used if the
flag bit is set. The signature is:
inttp_traverse(PyObject*self,visitprocvisit,void*arg);More information about Python’s garbage collection scheme can be found in section
Supporting Cyclic Garbage Collection
.
The
pointer is used by the garbage collector to detect reference cycles. A typical implementation of a
function simply calls
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:
staticintlocal_traverse(localobject*self,visitprocvisit,void*arg){Py_VISIT(self->args);Py_VISIT(self->kw);Py_VISIT(self->dict);return0;}Note that
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
module’s
function will include it.
Warning
When implementing
, only the members that the instance owns (by having
to them) must be visited. For instance, if an object supports weak references via the
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
requires the visit and arg parameters to local_traverse() to have these specific names; don’t name them just anything.
Instances of
hold a reference to their type. Their traversal function must therefore either visit
, 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
, doing this may lead to crashes in subclasses.
Inheritance:
Group:
,
,
This field is inherited by subtypes together with
and the
flag bit: the flag bit,
, and
are all inherited from the base type if they are all zero in the subtype.
.tp_clear
An optional pointer to a clear function for the garbage collector. This is only used if the
flag bit is set. The signature is:
inttp_clear(PyObject*);The
member function is used to break reference cycles in cyclic garbage detected by the garbage collector. Taken together, all
functions in the system must combine to break all reference cycles. This is subtle, and if in any doubt supply a
function. For example, the tuple type does not implement a
function, because it’s possible to prove that no reference cycle can be composed entirely of tuples. Therefore the
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
.
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(localobject*self){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
macro performs the operations in a safe order.
Note that
is not always called before an instance is deallocated. For example, when reference counting is enough to determine that an object is no longer used, the cyclic garbage collector is not involved and
is called directly.
Because the goal of
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
function to invoke
.
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,
, and
are all inherited from the base type if they are all zero in the subtype.
.tp_richcompare
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.
New in version 3.7.
Inheritance:
Group:
,
This field is inherited by subtypes together with
: a subtype inherits
and
when the subtype’s
and
are both NULL.
Default:
PyBaseObject_Type 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
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.
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.
When a type defined by a class statement has no
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
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
.
When a type’s __slots__ declaration does not contain a slot named __weakref__, the type inherits its
from its base type.
.tp_iter
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
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
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
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
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.
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 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,
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
).
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
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
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
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.
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
or
. Note that the
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,
should be set to -4 to indicate that the dictionary is at the very end of the structure.
The
should be regarded as write-only. To get the pointer to the dictionary call
. Calling
may need to allocate memory for the dictionary, so it is may be more efficient to call
when accessing an attribute on the object.
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
, this should not be a problem.
When a type defined by a class statement has no
declaration, and none of its base types has an instance variable dictionary, a dictionary slot is added to the instance layout and the
is set to that slot’s offset.
When a type defined by a class statement has a __slots__ declaration, the type inherits its
from its base type.
(Adding a slot named
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
, if the field is NULL then no
gets created for instances.
.tp_init
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
function returns an instance of some other type that is not a subtype of the original type, no
function is called; if
returns an instance of a subtype of the original type, the subtype’s
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
An optional pointer to an instance allocation function.
The function signature is:
PyObject*tp_alloc(PyTypeObject*self,Py_ssize_tnitems);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
, to force a standard heap allocation strategy.
For static subtypes, PyBaseObject_Type uses
. That is the recommended value for all statically defined types.
.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
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
, while for mutable types, most initialization should be deferred to
.
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
An optional pointer to an instance deallocation function. Its signature is:
voidtp_free(void*self);An initializer that is compatible with this signature is
.
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
and the value of the
flag bit.
For static subtypes, PyBaseObject_Type uses
.
.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
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 dynamically created classes, the Py_tp_bases
can be used instead of the bases argument of
. The argument form is preferred.
Warning
Multiple inheritance does not work well for statically defined types. If you set tp_bases to a tuple, Python will not raise an error, but some slots will only be inherited from the first base.
Inheritance:
This field is not inherited.
*
.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.
*
.tp_subclasses
List of weak references to subclasses. Internal use only.
Inheritance:
This field is not inherited.
*
.tp_weaklist
Weak reference list head, for weak references to this type object. Not inherited. Internal use only.
Inheritance:
This field is not inherited.
.tp_del
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
An optional pointer to an instance finalization function. Its signature is:
voidtp_finalize(PyObject*self);If
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.
should not mutate the current exception status; therefore, a recommended way to write a non-trivial finalizer is:
staticvoidlocal_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);}Also, note that, in a garbage collected Python,
may be called from any Python thread, not just the thread which created the object (if the object becomes part of a refcount cycle, that cycle might be collected by a garbage collection on any thread). This is not a problem for Python API calls, since the thread on which tp_dealloc is called will own the Global Interpreter Lock (GIL). However, if the object being destroyed in turn destroys objects from some other C or C++ library, care should be taken to ensure that destroying those objects on the thread which called tp_dealloc will not violate any assumptions of the library.
Inheritance:
This field is inherited by subtypes.
New in version 3.4.
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” (
)
.tp_vectorcall
Vectorcall function to use for calls of this type object. In other words, it is used to implement
for type.__call__. If tp_vectorcall is NULL, the default call implementation using
and
is used.
Inheritance:
This field is never inherited.
New in version 3.9: (the field exists since 3.8 but it’s only used since 3.9)
Static Types
Traditionally, types defined in C code are static, that is, a static
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
.nb_subtract
.nb_multiply
.nb_remainder
.nb_divmod
.nb_power
.nb_negative
.nb_positive
.nb_absolute
.nb_bool
.nb_invert
.nb_lshift
.nb_rshift
.nb_and
.nb_xor
.nb_or
.nb_int
void*
.nb_reserved
.nb_float
.nb_inplace_add
.nb_inplace_subtract
.nb_inplace_multiply
.nb_inplace_remainder
.nb_inplace_power
.nb_inplace_lshift
.nb_inplace_rshift
.nb_inplace_and
.nb_inplace_xor
.nb_inplace_or
.nb_floor_divide
.nb_true_divide
.nb_inplace_floor_divide
.nb_inplace_true_divide
.nb_index
.nb_matrix_multiply
.nb_inplace_matrix_multiply
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
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
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
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
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
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
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
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
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
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
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
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 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.
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 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
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
New 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 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 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 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 signature of this function is:
PySendResultam_send(PyObject*self,PyObject*arg,PyObject**result);See
for details. This slot may be set to NULL.
New 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)
typedefvoid(*releasebufferproc)(
*,
*)
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;PyObject*inst_dict;PyObject*weakreflist;}MyObject;staticPyTypeObjectMyObject_Type={PyVarObject_HEAD_INIT(NULL,0).tp_name="mymod.MyObject",.tp_basicsize=sizeof(MyObject),.tp_doc=PyDoc_STR("My objects"),.tp_weaklistoffset=offsetof(MyObject,weakreflist),.tp_dictoffset=offsetof(MyObject,inst_dict),.tp_flags=Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE|Py_TPFLAGS_HAVE_GC,.tp_new=myobj_new,.tp_traverse=(traverseproc)myobj_traverse,.tp_clear=(inquiry)myobj_clear,.tp_alloc=PyType_GenericNew,.tp_dealloc=(destructor)myobj_dealloc,.tp_repr=(reprfunc)myobj_repr,.tp_hash=(hashfunc)myobj_hash,.tp_richcompare=PyBaseObject_Type.tp_richcompare,};A str subclass that cannot be subclassed and cannot be called to create instances (e.g. uses a separate factory func) using
Py_TPFLAGS_DISALLOW_INSTANTIATION
flag:
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*),};