# 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
  次に属します: Limited API. (いくつかのメンバーのみが安定 ABI です。)

  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 `PyObject`, but every pointer to a Python object can be cast to a PyObject*.

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

  Py_ssize_t ob_refcnt
    次に属します: Stable ABI.

    The object's reference count, as returned by `Py_REFCNT`. Do not use this field directly; instead use functions and macros such as `Py_REFCNT`, `Py_INCREF()` and `Py_DecRef()`.

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

  PyTypeObject *ob_type
    次に属します: Stable ABI.

    The object's type. Do not use this field directly; use `Py_TYPE` and `Py_SET_TYPE()` instead.

type PyVarObject
  次に属します: Limited API. (いくつかのメンバーのみが安定 ABI です。)

  An extension of `PyObject` that adds the `ob_size` field. This is intended for objects that have some notion of length.

  As with `PyObject`, the members must not be accessed directly; instead use macros such as `Py_SIZE`, `Py_REFCNT` and `Py_TYPE`.

  Py_ssize_t ob_size
    次に属します: Stable ABI.

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

    Do not use this field directly; use `Py_SIZE` instead.

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

    To get an object's publicly exposed length, as returned by the Python function `len()`, use `PyObject_Length()` instead.

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。

PyTypeObject PyBaseObject_Type
  次に属します: Stable ABI.

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

int Py_Is(PyObject *x, PyObject *y)
  次に属します: Stable ABI (バージョン 3.10 より).

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

  Added in version 3.10.

int Py_IsNone(PyObject *x)
  次に属します: Stable ABI (バージョン 3.10 より).

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

  Added in version 3.10.

int Py_IsTrue(PyObject *x)
  次に属します: Stable ABI (バージョン 3.10 より).

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

  Added in version 3.10.

int Py_IsFalse(PyObject *x)
  次に属します: Stable ABI (バージョン 3.10 より).

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

  Added in version 3.10.

PyTypeObject *Py_TYPE(PyObject *o)
  戻り値: 借用参照。 次に属します: Stable ABI (バージョン 3.14 より).

  Get the type of the Python object o.

  The returned reference is borrowed from o. Do not release it with `Py_DECREF()` or similar.

  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`.

  Added in version 3.9.

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 `__class__` using `PyObject_SetAttrString()` or similar.

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

  If type is a heap type, 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.

  Added in version 3.9.

Py_ssize_t Py_SIZE(PyVarObject *o)

  Get the `ob_size` field of o.

  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 `ob_size` field of o to size.

  Added in version 3.9.

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
  次に属します: 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
  次に属します: 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
  次に属します: Stable ABI (バージョン 3.13 より).

  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
  次に属します: Stable ABI (バージョン 3.13 より).

  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)

  Added in version 3.9.

type PyMethodDef
  次に属します: Stable ABI (すべてのメンバーを含む).

  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).

  Added in version 3.7.

  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.

  Added in version 3.7.

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`.

  Added in version 3.9.

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)
  戻り値: 新しい参照。 次に属します: Stable ABI (バージョン 3.9 より).

  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`.

  参考

  `function.__module__`

  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`.

  Added in version 3.9.

PyObject *PyCFunction_NewEx(PyMethodDef *ml, PyObject *self, PyObject *module)
  戻り値: 新しい参照。 次に属します: Stable ABI.

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

PyObject *PyCFunction_New(PyMethodDef *ml, PyObject *self)
  戻り値: 新しい参照。 次に属します: Stable ABI (バージョン 3.4 より).

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

## Accessing attributes of extension types

type PyMemberDef
  次に属します: Stable ABI (すべてのメンバーを含む).

  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. 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 `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"`.

  バージョン 3.14 で変更: `Py_RELATIVE_OFFSET` is now allowed for `"__vectorcalloffset__"`, `"__dictoffset__"` and `"__weaklistoffset__"`.

PyObject *PyMember_GetOne(const char *obj_addr, struct PyMemberDef *m)
  次に属します: 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)
  次に属します: 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`.

Added in version 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:

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
  次に属します: Stable ABI (すべてのメンバーを含む).

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

typedef PyObject *(*getter)(PyObject*, void*)
  次に属します: Stable ABI.

  The `get` function takes one PyObject* parameter (the instance) and a user data 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*)
  次に属します: Stable ABI.

  `set` functions take two PyObject* parameters (the instance and the value to be set) and a user data 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。