共通のオブジェクト構造体 (common object structure)

Python では、オブジェクト型を定義する上で数多くの構造体が使われます。この節では三つの構造体とその利用方法について説明します。

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 PyObject and 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 reference counting.

type PyObject
Part of the Limited API. (Only some members are part of the stable ABI.)

全てのオブジェクト型はこの型を拡張したものです。 この型には、あるオブジェクトを指すポインタをオブジェクトとして Python から扱うのに必要な情報が入っています。 通常の "リリース" ビルドでは、この構造体にはオブジェクトの参照カウントとオブジェクトに対応する型オブジェクトだけが入っています。 実際には PyObject であることは宣言されていませんが、全ての Python オブジェクトへのポインタは PyObject* へキャストできます。 メンバにアクセスするには Py_REFCNT マクロと Py_TYPE マクロを使わなければなりません。

type PyVarObject
Part of the Limited API. (Only some members are part of the stable ABI.)

This is an extension of PyObject that adds the ob_size field. This is only used for objects that have some notion of length. This type does not often appear in the Python/C API. Access to the members must be done by using the macros Py_REFCNT, Py_TYPE, and Py_SIZE.

PyObject_HEAD

可変な長さを持たないオブジェクトを表現する新しい型を宣言するときに使うマクロです。 PyObject_HEAD マクロは次のように展開されます:

PyObject ob_base;

上にある PyObject のドキュメントを参照してください。

PyObject_VAR_HEAD

インスタンスごとに異なる長さを持つオブジェクトを表現する新しい型を宣言するときに使うマクロです。 PyObject_VAR_HEAD マクロは次のように展開されます:

PyVarObject ob_base;

上にある PyVarObject のドキュメントを参照してください。

int Py_Is(PyObject *x, PyObject *y)
Part of the Stable ABI since version 3.10.

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

バージョン 3.10 で追加.

int Py_IsNone(PyObject *x)
Part of the Stable ABI since version 3.10.

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

バージョン 3.10 で追加.

int Py_IsTrue(PyObject *x)
Part of the Stable ABI since version 3.10.

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

バージョン 3.10 で追加.

int Py_IsFalse(PyObject *x)
Part of the Stable ABI since version 3.10.

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

バージョン 3.10 で追加.

PyTypeObject *Py_TYPE(PyObject *o)

Get the type of the Python object o.

Return a borrowed reference.

Use the Py_SET_TYPE() function to set an object type.

バージョン 3.11 で変更: Py_TYPE() is changed to an inline static function. The parameter type is no longer const PyObject*.

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.

バージョン 3.9 で追加.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

Set the object o type to type.

バージョン 3.9 で追加.

Py_ssize_t Py_SIZE(PyVarObject *o)

Get the size of the Python object o.

Use the Py_SET_SIZE() function to set an object size.

バージョン 3.11 で変更: Py_SIZE() is changed to an inline static function. The parameter type is no longer const PyVarObject*.

void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)

Set the object o size to size.

バージョン 3.9 で追加.

PyObject_HEAD_INIT(type)

新しい PyObject 型のための初期値に展開するマクロです。このマクロは次のように展開されます。

_PyObject_EXTRA_INIT
1, type,
PyVarObject_HEAD_INIT(type, size)

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

_PyObject_EXTRA_INIT
1, type, size,

Implementing functions and methods

type PyCFunction
Part of the Stable ABI.

Type of the functions used to implement most Python callables in C. Functions of this type take two 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.

関数のシグネチャは次のとおりです

PyObject *PyCFunction(PyObject *self,
                      PyObject *args);
type PyCFunctionWithKeywords
Part of the Stable ABI.

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

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

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

PyObject *_PyCFunctionFast(PyObject *self,
                           PyObject *const *args,
                           Py_ssize_t nargs);
type _PyCFunctionFastWithKeywords

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

PyObject *_PyCFunctionFastWithKeywords(PyObject *self,
                                       PyObject *const *args,
                                       Py_ssize_t nargs,
                                       PyObject *kwnames);
type PyCMethod

Type of the functions used to implement Python callables in C with signature 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)

バージョン 3.9 で追加.

type PyMethodDef
Part of the Stable ABI (including all members).

拡張型のメソッドを記述する際に用いる構造体です。この構造体には 4 つのフィールドがあります:

const char *ml_name

Name of the method.

PyCFunction ml_meth

Pointer to the C implementation.

int ml_flags

Flags bits indicating how the call should be constructed.

const char *ml_doc

Points to the contents of the docstring.

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

The 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:

METH_VARARGS

PyCFunction 型のメソッドで典型的に使われる呼び出し規約です。関数は PyObject* 型の引数値を二つ要求します。最初の引数はメソッドの self オブジェクトです; モジュール関数の場合、これはモジュールオブジェクトです。第二のパラメタ (よく args と呼ばれます) は、全ての引数を表現するタプルオブジェクトです。パラメタは通常、 PyArg_ParseTuple()PyArg_UnpackTuple() で処理されます。

METH_KEYWORDS

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

METH_VARARGS | METH_KEYWORDS

Methods with these flags must be of 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 PyArg_ParseTupleAndKeywords().

METH_FASTCALL

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

バージョン 3.7 で追加.

バージョン 3.10 で変更: METH_FASTCALL is now part of the stable ABI.

METH_FASTCALL | METH_KEYWORDS

Extension of METH_FASTCALL supporting also keyword arguments, with methods of type _PyCFunctionFastWithKeywords. Keyword arguments are passed the same way as in the vectorcall protocol: there is an additional fourth 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.

バージョン 3.7 で追加.

METH_METHOD

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

METH_METHOD | METH_FASTCALL | METH_KEYWORDS

Extension of 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 PyCMethod, the same as for METH_FASTCALL | METH_KEYWORDS with defining_class argument added after self.

バージョン 3.9 で追加.

METH_NOARGS

Methods without parameters don't need to check whether arguments are given if they are listed with the METH_NOARGS flag. They need to be of 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, Py_UNUSED can be used to prevent a compiler warning.

METH_O

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

以下の二つの定数は、呼び出し規約を示すものではなく、クラスのメソッドとして使う際の束縛方式を示すものです。モジュールに対して定義された関数で用いてはなりません。メソッドに対しては、最大で一つしかこのフラグをセットできません。

METH_CLASS

メソッドの最初の引数には、型のインスタンスではなく型オブジェクトが渡されます。このフラグは組み込み関数 classmethod() を使って生成するのと同じ クラスメソッド (class method) を生成するために使われます。

METH_STATIC

メソッドの最初の引数には、型のインスタンスではなく NULL が渡されます。このフラグは、 staticmethod() を使って生成するのと同じ 静的メソッド (static method) を生成するために使われます。

もう一つの定数は、あるメソッドを同名の別のメソッド定義と置き換えるかどうかを制御します。

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 __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.

PyObject *PyCMethod_New(PyMethodDef *ml, PyObject *self, PyObject *module, PyTypeObject *cls)
Return value: New reference. Part of the Stable ABI since version 3.9.

Turn ml into a Python callable object. The caller must ensure that ml outlives the 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 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 None or NULL.

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

バージョン 3.9 で追加.

PyObject *PyCFunction_NewEx(PyMethodDef *ml, PyObject *self, PyObject *module)
Return value: New reference. Part of the Stable ABI.

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

PyObject *PyCFunction_New(PyMethodDef *ml, PyObject *self)
Return value: New reference. Part of the Stable ABI since version 3.4.

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

Accessing attributes of extension types

type PyMemberDef
Part of the Stable ABI (including all members).

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 tp_members slot.

Its fields are, in order:

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.

int type

The type of the member in the C struct. See Member types for the possible values.

Py_ssize_t offset

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

int flags

Zero or more of the Member flags, combined using bitwise OR.

const char *doc

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

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

For heap-allocated types (created using PyType_FromSpec() or similar), PyMemberDef may contain a definition for the special member "__vectorcalloffset__", corresponding to tp_vectorcall_offset in type objects. These must be defined with Py_T_PYSSIZET and Py_READONLY, 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 offsetof().)

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

バージョン 3.12 で変更: PyMemberDef is always available. Previously, it required including "structmember.h".

PyObject *PyMember_GetOne(const char *obj_addr, struct PyMemberDef *m)
Part of the Stable ABI.

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

バージョン 3.12 で変更: PyMember_GetOne is always available. Previously, it required including "structmember.h".

int PyMember_SetOne(char *obj_addr, struct PyMemberDef *m, PyObject *o)
Part of the Stable ABI.

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.

バージョン 3.12 で変更: PyMember_SetOne is always available. Previously, it required including "structmember.h".

Member flags

The following flags can be used with PyMemberDef.flags:

Py_READONLY

Not writable.

Py_AUDIT_READ

Emit an object.__getattr__ audit event before reading.

Py_RELATIVE_OFFSET

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

Can only be used as part of Py_tp_members slot when creating a class using negative basicsize. It is mandatory in that case.

This flag is only used in PyType_Slot. When setting tp_members during class creation, Python clears it and sets PyMemberDef.offset to the offset from the PyObject struct.

バージョン 3.10 で変更: The RESTRICTED, READ_RESTRICTED and WRITE_RESTRICTED macros available with #include "structmember.h" are deprecated. READ_RESTRICTED and RESTRICTED are equivalent to Py_AUDIT_READ; WRITE_RESTRICTED does nothing.

バージョン 3.12 で変更: The READONLY macro was renamed to Py_READONLY. The 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.

Member types

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 TypeError or ValueError is raised.

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

マクロ名

C の型

Python の型

Py_T_BYTE

char

int

Py_T_SHORT

short

int

Py_T_INT

int

int

Py_T_LONG

long

int

Py_T_LONGLONG

long long

int

Py_T_UBYTE

unsigned char

int

Py_T_UINT

unsigned int

int

Py_T_USHORT

unsigned short

int

Py_T_ULONG

unsigned long

int

Py_T_ULONGLONG

unsigned long long

int

Py_T_PYSSIZET

Py_ssize_t

int

Py_T_FLOAT

float

float

Py_T_DOUBLE

double

float

Py_T_BOOL

char (written as 0 or 1)

bool

Py_T_STRING

const char* (*)

str (RO)

Py_T_STRING_INPLACE

const char[] (*)

str (RO)

Py_T_CHAR

char (0-127)

str (**)

Py_T_OBJECT_EX

PyObject*

object (D)

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

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

(RO): Implies Py_READONLY.

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

バージョン 3.12 で追加: 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:

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.

T_NONE

Always None. Must be used with Py_READONLY.

Defining Getters and Setters

type PyGetSetDef
Part of the Stable ABI (including all members).

型のプロパティのようなアクセスを定義するための構造体です。 PyTypeObject.tp_getset スロットの説明も参照してください。

const char *name

属性名

getter get

C function to get the attribute.

setter set

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

const char *doc

任意のドキュメンテーション文字列

void *closure

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

typedef PyObject *(*getter)(PyObject*, void*)
Part of the Stable ABI.

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

成功または失敗時に NULL と例外の集合にされたときは新しい参照を返します。

typedef int (*setter)(PyObject*, PyObject*, void*)
Part of the Stable ABI.

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

属性を削除する場合は、2 番目のパラメータに NULL を指定します。成功した場合は 0 を、失敗した場合は -1 を例外として返します。