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。)*

   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
    * 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。)*

   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)
    * 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*.

   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".

   Added in version 3.9.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

   Set the object *o* type to *type*.

   Added in version 3.9.

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*.

   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。
