.. highlight:: c

.. _common-structs:

Common Object Structures

There are a large number of structures which are used in the definition of object types for Python. This section describes these structures and how they are used.

Base object types and macros

All Python objects ultimately share a small number of fields at the beginning of the object's representation in memory. These are represented by the :c:type:PyObject and :c:type:PyVarObject types, which are defined, in turn, by the expansions of some macros also used, whether directly or indirectly, in the definition of all other Python objects. Additional macros can be found under :ref:reference counting <countingrefs>.

.. c:type:: PyObject

All object types are extensions of this type. This is a type which contains the information Python needs to treat a pointer to an object as an object. In a normal "release" build, it contains only the object's reference count and a pointer to the corresponding type object. Nothing is actually declared to be a :c:type:PyObject, but every pointer to a Python object can be cast to a :c:expr:PyObject*.

The members must not be accessed directly; instead use macros such as :c:macro:Py_REFCNT and :c:macro:Py_TYPE.

.. c:member:: Py_ssize_t ob_refcnt

  The object's reference count, as returned by :c:macro:`Py_REFCNT`.
  Do not use this field directly; instead use functions and macros such as
  :c:macro:`!Py_REFCNT`, :c:func:`Py_INCREF` and :c:func:`Py_DecRef`.

  The field type may be different from ``Py_ssize_t``, depending on
  build configuration and platform.

.. c:member:: PyTypeObject* ob_type

  The object's type.
  Do not use this field directly; use :c:macro:`Py_TYPE` and
  :c:func:`Py_SET_TYPE` instead.

.. c:member:: PyMutex ob_mutex

  A :ref:`per-object lock <per-object-locks>`, present only in the :term:`free-threaded <free threading>`
  build (when :c:macro:`Py_GIL_DISABLED` is defined).

  This field is **reserved for use by the critical section API**
  (:c:macro:`Py_BEGIN_CRITICAL_SECTION` / :c:macro:`Py_END_CRITICAL_SECTION`).
  Do **not** lock it directly with ``PyMutex_Lock``; doing so can cause
  deadlocks.  If you need your own lock, add a separate :c:type:`PyMutex`
  field to your object struct.

  .. versionadded:: 3.13

.. c:type:: PyVarObject

An extension of :c:type:PyObject that adds the :c:member:~PyVarObject.ob_size field. This is intended for objects that have some notion of length.

As with :c:type:!PyObject, the members must not be accessed directly; instead use macros such as :c:macro:Py_SIZE, :c:macro:Py_REFCNT and :c:macro:Py_TYPE.

.. c:member:: Py_ssize_t ob_size

  A size field, whose contents should be considered an object's internal
  implementation detail.

  Do not use this field directly; use :c:macro:`Py_SIZE` instead.

  Object creation functions such as :c:func:`PyObject_NewVar` will
  generally set this field to the requested size (number of items).
  After creation, arbitrary values can be stored in :c:member:`!ob_size`
  using :c:macro:`Py_SET_SIZE`.

  To get an object's publicly exposed length, as returned by
  the Python function :py:func:`len`, use :c:func:`PyObject_Length`
  instead.

.. c:macro:: PyObject_HEAD

This is a macro used when declaring new types which represent objects without a varying length. The PyObject_HEAD macro expands to::

  PyObject ob_base;

See documentation of :c:type:PyObject above.

.. c:macro:: PyObject_VAR_HEAD

This is a macro used when declaring new types which represent objects with a length that varies from instance to instance. The PyObject_VAR_HEAD macro expands to::

  PyVarObject ob_base;

See documentation of :c:type:PyVarObject above.

.. c:var:: PyTypeObject PyBaseObject_Type

The base class of all other objects, the same as :class:object in Python.

.. c:function:: int Py_Is(PyObject *x, PyObject *y)

Test if the x object is the y object, the same as x is y in Python.

.. versionadded:: 3.10

.. c:function:: int Py_IsNone(PyObject *x)

Test if an object is the None singleton, the same as x is None in Python.

.. versionadded:: 3.10

.. c:function:: int Py_IsTrue(PyObject *x)

Test if an object is the True singleton, the same as x is True in Python.

.. versionadded:: 3.10

.. c:function:: int Py_IsFalse(PyObject *x)

Test if an object is the False singleton, the same as x is False in Python.

.. versionadded:: 3.10

.. c:function:: PyTypeObject* Py_TYPE(PyObject *o)

Get the type of the Python object o.

The returned reference is :term:borrowed <borrowed reference> from o. Do not release it with :c:func:Py_DECREF or similar.

.. versionchanged:: 3.11 :c:func:Py_TYPE() is changed to an inline static function. The parameter type is no longer :c:expr:const PyObject*.

.. c:function:: int Py_IS_TYPE(PyObject *o, PyTypeObject *type)

Return non-zero if the object o type is type. Return zero otherwise. Equivalent to: Py_TYPE(o) == type.

.. versionadded:: 3.9

.. c:function:: void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

Set the type of object o to type, without any checking or reference counting.

This is a very low-level operation. Consider instead setting the Python attribute :attr:~object.__class__ using :c:func:PyObject_SetAttrString or similar.

Note that assigning an incompatible type can lead to undefined behavior.

If type is a :ref:heap type <heap-types>, the caller must create a new reference to it. Similarly, if the old type of o is a heap type, the caller must release a reference to that type.

.. versionadded:: 3.9

.. c:function:: Py_ssize_t Py_SIZE(PyVarObject *o)

Get the :c:member:~PyVarObject.ob_size field of o.

.. versionchanged:: 3.11 :c:func:Py_SIZE() is changed to an inline static function. The parameter type is no longer :c:expr:const PyVarObject*.

.. c:function:: void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)

Set the :c:member:~PyVarObject.ob_size field of o to size.

.. versionadded:: 3.9

.. c:macro:: PyObject_HEAD_INIT(type)

This is a macro which expands to initialization values for a new :c:type:PyObject type. This macro expands to::

  _PyObject_EXTRA_INIT
  1, type,

.. c:macro:: PyVarObject_HEAD_INIT(type, size)

This is a macro which expands to initialization values for a new :c:type:PyVarObject type, including the :c:member:~PyVarObject.ob_size field. This macro expands to::

  _PyObject_EXTRA_INIT
  1, type, size,

Implementing functions and methods

.. c:type:: PyCFunction

Type of the functions used to implement most Python callables in C. Functions of this type take two :c:expr:PyObject* parameters and return one such value. If the return value is NULL, an exception shall have been set. If not NULL, the return value is interpreted as the return value of the function as exposed in Python. The function must return a new reference.

The function signature is::

  PyObject *PyCFunction(PyObject *self,
                        PyObject *args);

.. c:type:: PyCFunctionWithKeywords

Type of the functions used to implement Python callables in C with signature :ref:METH_VARARGS | METH_KEYWORDS <METH_VARARGS-METH_KEYWORDS>. The function signature is::

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

.. c:type:: PyCFunctionFast

Type of the functions used to implement Python callables in C with signature :c:macro:METH_FASTCALL. The function signature is::

  PyObject *PyCFunctionFast(PyObject *self,
                            PyObject *const *args,
                            Py_ssize_t nargs);

.. c:type:: PyCFunctionFastWithKeywords

Type of the functions used to implement Python callables in C with signature :ref:METH_FASTCALL | METH_KEYWORDS <METH_FASTCALL-METH_KEYWORDS>. The function signature is::

  PyObject *PyCFunctionFastWithKeywords(PyObject *self,
                                        PyObject *const *args,
                                        Py_ssize_t nargs,
                                        PyObject *kwnames);

.. c:type:: PyCMethod

Type of the functions used to implement Python callables in C with signature :ref:METH_METHOD | METH_FASTCALL | METH_KEYWORDS <METH_METHOD-METH_FASTCALL-METH_KEYWORDS>. The function signature is::

  PyObject *PyCMethod(PyObject *self,
                      PyTypeObject *defining_class,
                      PyObject *const *args,
                      Py_ssize_t nargs,
                      PyObject *kwnames)

.. versionadded:: 3.9

.. c:type:: PyMethodDef

Structure used to describe a method of an extension type. This structure has four fields:

.. c:member:: const char *ml_name

  Name of the method.

  A ``NULL`` *ml_name* marks the end of a :c:type:`!PyMethodDef` array.

.. c:member:: PyCFunction ml_meth

  Pointer to the C implementation.

.. c:member:: int ml_flags

  Flags bits indicating how the call should be constructed.

.. c:member:: const char *ml_doc

  Points to the contents of the docstring.

The :c:member:~PyMethodDef.ml_meth is a C function pointer. The functions may be of different types, but they always return :c:expr:PyObject*. If the function is not of the :c:type:PyCFunction, the compiler will require a cast in the method table. Even though :c:type:PyCFunction defines the first parameter as :c:expr:PyObject*, it is common that the method implementation uses the specific C type of the self object.

The :c:member:~PyMethodDef.ml_flags field is a bitfield which can include the following flags. The individual flags indicate either a calling convention or a binding convention.

There are these calling conventions:

.. c:macro:: METH_VARARGS

This is the typical calling convention, where the methods have the type :c:type:PyCFunction. The function expects two :c:expr:PyObject* values. The first one is the self object for methods; for module functions, it is the module object. The second parameter (often called args) is a tuple object representing all arguments. This parameter is typically processed using :c:func:PyArg_ParseTuple or :c:func:PyArg_UnpackTuple.

.. c:macro:: METH_KEYWORDS

Can only be used in certain combinations with other flags: :ref:METH_VARARGS | METH_KEYWORDS <METH_VARARGS-METH_KEYWORDS>, :ref:METH_FASTCALL | METH_KEYWORDS <METH_FASTCALL-METH_KEYWORDS> and :ref:METH_METHOD | METH_FASTCALL | METH_KEYWORDS <METH_METHOD-METH_FASTCALL-METH_KEYWORDS>.

.. _METH_VARARGS-METH_KEYWORDS:

:c:expr:METH_VARARGS | METH_KEYWORDS Methods with these flags must be of type :c:type:PyCFunctionWithKeywords. The function expects three parameters: self, args, kwargs where kwargs is a dictionary of all the keyword arguments or possibly NULL if there are no keyword arguments. The parameters are typically processed using :c:func:PyArg_ParseTupleAndKeywords.

.. c:macro:: METH_FASTCALL

Fast calling convention supporting only positional arguments. The methods have the type :c:type:PyCFunctionFast. The first parameter is self, the second parameter is a C array of :c:expr:PyObject* values indicating the arguments and the third parameter is the number of arguments (the length of the array).

.. versionadded:: 3.7

.. versionchanged:: 3.10

  ``METH_FASTCALL`` is now part of the :ref:`stable ABI <stable-abi>`.

.. _METH_FASTCALL-METH_KEYWORDS:

:c:expr:METH_FASTCALL | METH_KEYWORDS Extension of :c:macro:METH_FASTCALL supporting also keyword arguments, with methods of type :c:type:PyCFunctionFastWithKeywords. Keyword arguments are passed the same way as in the :ref:vectorcall protocol <vectorcall>: there is an additional fourth :c:expr:PyObject* parameter which is a tuple representing the names of the keyword arguments (which are guaranteed to be strings) or possibly NULL if there are no keywords. The values of the keyword arguments are stored in the args array, after the positional arguments.

.. versionadded:: 3.7

.. c:macro:: METH_METHOD

Can only be used in the combination with other flags: :ref:METH_METHOD | METH_FASTCALL | METH_KEYWORDS <METH_METHOD-METH_FASTCALL-METH_KEYWORDS>.

.. _METH_METHOD-METH_FASTCALL-METH_KEYWORDS:

:c:expr:METH_METHOD | METH_FASTCALL | METH_KEYWORDS Extension of :ref:METH_FASTCALL | METH_KEYWORDS <METH_FASTCALL-METH_KEYWORDS> supporting the defining class, that is, the class that contains the method in question. The defining class might be a superclass of Py_TYPE(self).

The method needs to be of type :c:type:PyCMethod, the same as for METH_FASTCALL | METH_KEYWORDS with defining_class argument added after self.

.. versionadded:: 3.9

.. c:macro:: METH_NOARGS

Methods without parameters don't need to check whether arguments are given if they are listed with the :c:macro:METH_NOARGS flag. They need to be of type :c:type:PyCFunction. The first parameter is typically named self and will hold a reference to the module or object instance. In all cases the second parameter will be NULL.

The function must have 2 parameters. Since the second parameter is unused, :c:macro:Py_UNUSED can be used to prevent a compiler warning.

.. c:macro:: METH_O

Methods with a single object argument can be listed with the :c:macro:METH_O flag, instead of invoking :c:func:PyArg_ParseTuple with a "O" argument. They have the type :c:type:PyCFunction, with the self parameter, and a :c:expr:PyObject* parameter representing the single argument.

These two constants are not used to indicate the calling convention but the binding when used with methods of classes. These may not be used for functions defined for modules. At most one of these flags may be set for any given method.

.. c:macro:: METH_CLASS

.. index:: pair: built-in function; classmethod

The method will be passed the type object as the first parameter rather than an instance of the type. This is used to create class methods, similar to what is created when using the :func:classmethod built-in function.

.. c:macro:: METH_STATIC

.. index:: pair: built-in function; staticmethod

The method will be passed NULL as the first parameter rather than an instance of the type. This is used to create static methods, similar to what is created when using the :func:staticmethod built-in function.

One other constant controls whether a method is loaded in place of another definition with the same method name.

.. c:macro:: METH_COEXIST

The method will be loaded in place of existing definitions. Without METH_COEXIST, the default is to skip repeated definitions. Since slot wrappers are loaded before the method table, the existence of a sq_contains slot, for example, would generate a wrapped method named :meth:~object.__contains__ and preclude the loading of a corresponding PyCFunction with the same name. With the flag defined, the PyCFunction will be loaded in place of the wrapper object and will co-exist with the slot. This is helpful because calls to PyCFunctions are optimized more than wrapper object calls.

.. c:var:: PyTypeObject PyCMethod_Type

The type object corresponding to Python C method objects. This is available as :class:types.BuiltinMethodType in the Python layer.

.. c:function:: int PyCMethod_Check(PyObject *op)

Return true if op is an instance of the :c:type:PyCMethod_Type type or a subtype of it. This function always succeeds.

.. c:function:: int PyCMethod_CheckExact(PyObject *op)

This is the same as :c:func:PyCMethod_Check, but does not account for subtypes.

.. c:function:: PyObject * PyCMethod_New(PyMethodDef *ml, PyObject *self, PyObject *module, PyTypeObject *cls)

Turn ml into a Python :term:callable object. The caller must ensure that ml outlives the :term:callable. Typically, ml is defined as a static variable.

The self parameter will be passed as the self argument to the C function in ml->ml_meth when invoked. self can be NULL.

The :term:callable object's __module__ attribute can be set from the given module argument. module should be a Python string, which will be used as name of the module the function is defined in. If unavailable, it can be set to :const:None or NULL.

.. seealso:: :attr:function.__module__

The cls parameter will be passed as the defining_class argument to the C function. Must be set if :c:macro:METH_METHOD is set on ml->ml_flags.

.. versionadded:: 3.9

.. c:var:: PyTypeObject PyCFunction_Type

The type object corresponding to Python C function objects. This is available as :class:types.BuiltinFunctionType in the Python layer.

.. c:function:: int PyCFunction_Check(PyObject *op)

Return true if op is an instance of the :c:type:PyCFunction_Type type or a subtype of it. This function always succeeds.

.. c:function:: int PyCFunction_CheckExact(PyObject *op)

This is the same as :c:func:PyCFunction_Check, but does not account for subtypes.

.. c:function:: PyObject * PyCFunction_NewEx(PyMethodDef *ml, PyObject *self, PyObject *module)

Equivalent to PyCMethod_New(ml, self, module, NULL).

.. c:function:: PyObject * PyCFunction_New(PyMethodDef *ml, PyObject *self)

Equivalent to PyCMethod_New(ml, self, NULL, NULL).

.. c:function:: int PyCFunction_GetFlags(PyObject *func)

Get the function's flags on func as they were passed to :c:member:~PyMethodDef.ml_flags.

If func is not a C function object, this fails with an exception. func must not be NULL.

This function returns the function's flags on success, and -1 with an exception set on failure.

.. c:function:: int PyCFunction_GET_FLAGS(PyObject *func)

This is the same as :c:func:PyCFunction_GetFlags, but without error or type checking.

.. c:function:: PyCFunction PyCFunction_GetFunction(PyObject *func)

Get the function pointer on func as it was passed to :c:member:~PyMethodDef.ml_meth.

If func is not a C function object, this fails with an exception. func must not be NULL.

This function returns the function pointer on success, and NULL with an exception set on failure.

.. c:function:: int PyCFunction_GET_FUNCTION(PyObject *func)

This is the same as :c:func:PyCFunction_GetFunction, but without error or type checking.

.. c:function:: PyObject *PyCFunction_GetSelf(PyObject *func)

Get the "self" object on func. This is the object that would be passed to the first argument of a :c:type:PyCFunction. For C function objects created through a :c:type:PyMethodDef on a :c:type:PyModuleDef, this is the resulting module object.

If func is not a C function object, this fails with an exception. func must not be NULL.

This function returns a :term:borrowed reference to the "self" object on success, and NULL with an exception set on failure.

.. c:function:: PyObject *PyCFunction_GET_SELF(PyObject *func)

This is the same as :c:func:PyCFunction_GetSelf, but without error or type checking.

Accessing attributes of extension types

.. c:type:: PyMemberDef

Structure which describes an attribute of a type which corresponds to a C struct member. When defining a class, put a NULL-terminated array of these structures in the :c:member:~PyTypeObject.tp_members slot.

Its fields are, in order:

.. c:member:: const char* name

     Name of the member.
     A NULL value marks the end of a ``PyMemberDef[]`` array.

     The string should be static, no copy is made of it.

.. c:member:: int type

  The type of the member in the C struct.
  See :ref:`PyMemberDef-types` for the possible values.

.. c:member:: Py_ssize_t offset

  The offset in bytes that the member is located on the type’s object struct.

.. c:member:: int flags

  Zero or more of the :ref:`PyMemberDef-flags`, combined using bitwise OR.

.. c:member:: const char* doc

  The docstring, or NULL.
  The string should be static, no copy is made of it.
  Typically, it is defined using :c:macro:`PyDoc_STR`.

By default (when :c:member:~PyMemberDef.flags is 0), members allow both read and write access. Use the :c:macro:Py_READONLY flag for read-only access. Certain types, like :c:macro:Py_T_STRING, imply :c:macro:Py_READONLY. Only :c:macro:Py_T_OBJECT_EX (and legacy :c:macro:T_OBJECT) members can be deleted.

.. _pymemberdef-offsets:

For heap-allocated types (created using :c:func:PyType_FromSpec or similar), PyMemberDef may contain a definition for the special member "__vectorcalloffset__", corresponding to :c:member:~PyTypeObject.tp_vectorcall_offset in type objects. This member must be defined with Py_T_PYSSIZET, and either Py_READONLY or Py_READONLY | Py_RELATIVE_OFFSET. For example::

  static PyMemberDef spam_type_members[] = {
      {"__vectorcalloffset__", Py_T_PYSSIZET,
       offsetof(Spam_object, vectorcall), Py_READONLY},
      {NULL}  /* Sentinel */
  };

(You may need to #include <stddef.h> for :c:func:!offsetof.)

The legacy offsets :c:member:~PyTypeObject.tp_dictoffset and :c:member:~PyTypeObject.tp_weaklistoffset can be defined similarly using "__dictoffset__" and "__weaklistoffset__" members, but extensions are strongly encouraged to use :c:macro:Py_TPFLAGS_MANAGED_DICT and :c:macro:Py_TPFLAGS_MANAGED_WEAKREF instead.

.. versionchanged:: 3.12

  ``PyMemberDef`` is always available.
  Previously, it required including ``"structmember.h"``.

.. versionchanged:: 3.14

  :c:macro:`Py_RELATIVE_OFFSET` is now allowed for
  ``"__vectorcalloffset__"``, ``"__dictoffset__"`` and
  ``"__weaklistoffset__"``.

.. c:function:: PyObject* PyMember_GetOne(const char *obj_addr, struct PyMemberDef *m)

Get an attribute belonging to the object at address obj_addr. The attribute is described by PyMemberDef m. Returns NULL on error.

.. versionchanged:: 3.12

  ``PyMember_GetOne`` is always available.
  Previously, it required including ``"structmember.h"``.

.. c:function:: int PyMember_SetOne(char *obj_addr, struct PyMemberDef *m, PyObject *o)

Set an attribute belonging to the object at address obj_addr to object o. The attribute to set is described by PyMemberDef m. Returns 0 if successful and a negative value on failure.

.. versionchanged:: 3.12

  ``PyMember_SetOne`` is always available.
  Previously, it required including ``"structmember.h"``.

.. _PyMemberDef-flags:

Member flags ^^^^^^^^^^^^

The following flags can be used with :c:member:PyMemberDef.flags:

.. c:macro:: Py_READONLY

Not writable.

.. c:macro:: Py_AUDIT_READ

Emit an object.__getattr__ :ref:audit event <audit-events> before reading.

.. c:macro:: Py_RELATIVE_OFFSET

Indicates that the :c:member:~PyMemberDef.offset of this PyMemberDef entry indicates an offset from the subclass-specific data, rather than from PyObject.

Can only be used as part of the :c:data:Py_tp_members :c:type:slot <PyType_Slot> when creating a class using negative :c:member:~PyType_Spec.basicsize. It is mandatory in that case. When setting :c:member:~PyTypeObject.tp_members from the slot during class creation, Python clears the flag and sets :c:member:PyMemberDef.offset to the offset from the PyObject struct.

.. index:: single: READ_RESTRICTED (C macro) single: WRITE_RESTRICTED (C macro) single: RESTRICTED (C macro)

.. versionchanged:: 3.10

The :c:macro:!RESTRICTED, :c:macro:!READ_RESTRICTED and :c:macro:!WRITE_RESTRICTED macros available with #include "structmember.h" are deprecated. :c:macro:!READ_RESTRICTED and :c:macro:!RESTRICTED are equivalent to :c:macro:Py_AUDIT_READ; :c:macro:!WRITE_RESTRICTED does nothing.

.. index:: single: READONLY (C macro)

.. versionchanged:: 3.12

The :c:macro:!READONLY macro was renamed to :c:macro:Py_READONLY. The :c:macro:!PY_AUDIT_READ macro was renamed with the Py_ prefix. The new names are now always available. Previously, these required #include "structmember.h". The header is still available and it provides the old names.

.. _PyMemberDef-types:

Member types ^^^^^^^^^^^^

:c:member:PyMemberDef.type can be one of the following macros corresponding to various C types. When the member is accessed in Python, it will be converted to the equivalent Python type. When it is set from Python, it will be converted back to the C type. If that is not possible, an exception such as :exc:TypeError or :exc:ValueError is raised.

Unless marked (D), attributes defined this way cannot be deleted using e.g. :keyword:del or :py:func:delattr.

================================ ============================= ====================== Macro name C type Python type ================================ ============================= ====================== .. c:macro:: Py_T_BYTE :c:expr:char :py:class:int .. c:macro:: Py_T_SHORT :c:expr:short :py:class:int .. c:macro:: Py_T_INT :c:expr:int :py:class:int .. c:macro:: Py_T_LONG :c:expr:long :py:class:int .. c:macro:: Py_T_LONGLONG :c:expr:long long :py:class:int .. c:macro:: Py_T_UBYTE :c:expr:unsigned char :py:class:int .. c:macro:: Py_T_UINT :c:expr:unsigned int :py:class:int .. c:macro:: Py_T_USHORT :c:expr:unsigned short :py:class:int .. c:macro:: Py_T_ULONG :c:expr:unsigned long :py:class:int .. c:macro:: Py_T_ULONGLONG :c:expr:unsigned long long :py:class:int .. c:macro:: Py_T_PYSSIZET :c:expr:Py_ssize_t :py:class:int .. c:macro:: Py_T_FLOAT :c:expr:float :py:class:float .. c:macro:: Py_T_DOUBLE :c:expr:double :py:class:float .. c:macro:: Py_T_BOOL :c:expr:char :py:class:bool (written as 0 or 1) .. c:macro:: Py_T_STRING :c:expr:const char * () :py:class:str (RO) .. c:macro:: Py_T_STRING_INPLACE :c:expr:const char[] () :py:class:str (RO) .. c:macro:: Py_T_CHAR :c:expr:char (0-127) :py:class:str (**) .. c:macro:: Py_T_OBJECT_EX :c:expr:PyObject * :py:class:object (D) ================================ ============================= ======================

(*): Zero-terminated, UTF8-encoded C string. With :c:macro:!Py_T_STRING the C representation is a pointer; with :c:macro:!Py_T_STRING_INPLACE the string is stored directly in the structure.

(**): String of length 1. Only ASCII is accepted.

(RO): Implies :c:macro:Py_READONLY.

(D): Can be deleted, in which case the pointer is set to NULL. Reading a NULL pointer raises :py:exc:AttributeError.

.. index:: single: T_BYTE (C macro) single: T_SHORT (C macro) single: T_INT (C macro) single: T_LONG (C macro) single: T_LONGLONG (C macro) single: T_UBYTE (C macro) single: T_USHORT (C macro) single: T_UINT (C macro) single: T_ULONG (C macro) single: T_ULONGULONG (C macro) single: T_PYSSIZET (C macro) single: T_FLOAT (C macro) single: T_DOUBLE (C macro) single: T_BOOL (C macro) single: T_CHAR (C macro) single: T_STRING (C macro) single: T_STRING_INPLACE (C macro) single: T_OBJECT_EX (C macro) single: structmember.h

.. versionadded:: 3.12

In previous versions, the macros were only available with #include "structmember.h" and were named without the Py_ prefix (e.g. as T_INT). The header is still available and contains the old names, along with the following deprecated types:

.. c:macro:: T_OBJECT

  Like ``Py_T_OBJECT_EX``, but ``NULL`` is converted to ``None``.
  This results in surprising behavior in Python: deleting the attribute
  effectively sets it to ``None``.

.. c:macro:: T_NONE

  Always ``None``. Must be used with :c:macro:`Py_READONLY`.

Defining Getters and Setters ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. c:type:: PyGetSetDef

Structure to define property-like access for a type. See also description of the :c:member:PyTypeObject.tp_getset slot.

.. c:member:: const char* name

  attribute name

.. c:member:: getter get

  C function to get the attribute.

.. c:member:: setter set

  Optional C function to set or delete the attribute.
  If ``NULL``, the attribute is read-only.

.. c:member:: const char* doc

  optional docstring

.. c:member:: void* closure

  Optional user data pointer, providing additional data for getter and setter.

.. c:type:: PyObject *(*getter)(PyObject *, void *)

The get function takes one :c:expr:PyObject* parameter (the instance) and a user data pointer (the associated closure):

It should return a new reference on success or NULL with a set exception on failure.

.. c:type:: int (*setter)(PyObject *, PyObject *, void *)

set functions take two :c:expr:PyObject* parameters (the instance and the value to be set) and a user data pointer (the associated closure):

In case the attribute should be deleted the second parameter is NULL. Should return 0 on success or -1 with a set exception on failure.