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.

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_REFCNT(PyObject *o)

Get the reference count of the Python object o.

Use the Py_SET_REFCNT() function to set an object reference count.

バージョン 3.11 で変更: The parameter type is no longer const PyObject*.

バージョン 3.10 で変更: Py_REFCNT() is changed to the inline static function.

void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)

Set the object o reference counter to refcnt.

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() や 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.

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. Its fields are:

Field	C Type	Meaning
name	const char *	name of the member
type	int	the type of the member in the C struct
offset	Py_ssize_t	the offset in bytes that the member is located on the type's object struct
flags	int	flag bits indicating if the field should be read-only or writable
doc	const char *	points to the contents of the docstring

type can be one of many T_ macros corresponding to various C types. When the member is accessed in Python, it will be converted to the equivalent Python type.

マクロ名	C の型
T_SHORT	short
T_INT	int
T_LONG	long
T_FLOAT	float
T_DOUBLE	double
T_STRING	const char *
T_OBJECT	PyObject *
T_OBJECT_EX	PyObject *
T_CHAR	char
T_BYTE	char
T_UBYTE	unsigned char
T_UINT	unsigned int
T_USHORT	unsigned short
T_ULONG	unsigned long
T_BOOL	char
T_LONGLONG	long long
T_ULONGLONG	unsigned long long
T_PYSSIZET	Py_ssize_t

T_OBJECT and T_OBJECT_EX differ in that T_OBJECT returns None if the member is NULL and T_OBJECT_EX raises an AttributeError. Try to use T_OBJECT_EX over T_OBJECT because T_OBJECT_EX handles use of the del statement on that attribute more correctly than T_OBJECT.

flags can be 0 for write and read access or READONLY for read-only access. Using T_STRING for type implies READONLY. T_STRING data is interpreted as UTF-8. Only T_OBJECT and T_OBJECT_EX members can be deleted. (They are set to NULL).

Heap allocated types (created using PyType_FromSpec() or similar), PyMemberDef may contain definitions for the special members __dictoffset__, __weaklistoffset__ and __vectorcalloffset__, corresponding to tp_dictoffset, tp_weaklistoffset and tp_vectorcall_offset in type objects. These must be defined with T_PYSSIZET and READONLY, for example:

static PyMemberDef spam_type_members[] = {
    {"__dictoffset__", T_PYSSIZET, offsetof(Spam_object, dict), READONLY},
    {NULL}  /* Sentinel */
};

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.

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.

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。

Field	C Type	Meaning
name	const char *	属性名
get	getter	C function to get the attribute
set	setter	optional C function to set or delete the attribute, if omitted the attribute is readonly
doc	const char *	任意のドキュメンテーション文字列
closure	void *	optional function pointer, providing additional data for getter and setter

get 関数は PyObject* パラメータ (インスタンス) と関数ポインタ (関連する``closure``) を1つ受け取ります。

typedef PyObject *(*getter)(PyObject *, void *);

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。

set 関数は PyObject* パラメータ (インスタンスとセットされるべき値) と関数ポインタ (関連する``closure``) を受け取ります。

typedef int (*setter)(PyObject *, PyObject *, void *);

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。