Call プロトコル
***************

CPython supports two different calling protocols: *tp_call* and
vectorcall.


The *tp_call* Protocol
======================

Instances of classes that set "tp_call" are callable. The signature of
the slot is:

   PyObject *tp_call(PyObject *callable, PyObject *args, PyObject *kwargs);

A call is made using a tuple for the positional arguments and a dict
for the keyword arguments, similarly to "callable(*args, **kwargs)" in
Python code. *args* must be non-NULL (use an empty tuple if there are
no arguments) but *kwargs* may be *NULL* if there are no keyword
arguments.

This convention is not only used by *tp_call*: "tp_new" and "tp_init"
also pass arguments this way.

To call an object, use "PyObject_Call()" or another call API.


The Vectorcall Protocol
=======================

バージョン 3.9 で追加.

The vectorcall protocol was introduced in **PEP 590** as an additional
protocol for making calls more efficient.

As rule of thumb, CPython will prefer the vectorcall for internal
calls if the callable supports it. However, this is not a hard rule.
Additionally, some third-party extensions use *tp_call* directly
(rather than using "PyObject_Call()"). Therefore, a class supporting
vectorcall must also implement "tp_call". Moreover, the callable must
behave the same regardless of which protocol is used. The recommended
way to achieve this is by setting "tp_call" to "PyVectorcall_Call()".
This bears repeating:

警告:

  A class supporting vectorcall **must** also implement "tp_call" with
  the same semantics.

A class should not implement vectorcall if that would be slower than
*tp_call*. For example, if the callee needs to convert the arguments
to an args tuple and kwargs dict anyway, then there is no point in
implementing vectorcall.

Classes can implement the vectorcall protocol by enabling the
"Py_TPFLAGS_HAVE_VECTORCALL" flag and setting "tp_vectorcall_offset"
to the offset inside the object structure where a *vectorcallfunc*
appears. This is a pointer to a function with the following signature:

typedef PyObject *(*vectorcallfunc)(PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwnames)

* *callable* is the object being called.

* *args* is a C array consisting of the positional arguments followed
  by the
     values of the keyword arguments. This can be *NULL* if there are
     no arguments.

* *nargsf* is the number of positional arguments plus possibly the
     "PY_VECTORCALL_ARGUMENTS_OFFSET" flag. To get the actual number
     of positional arguments from *nargsf*, use
     "PyVectorcall_NARGS()".

* *kwnames* is a tuple containing the names of the keyword arguments;
     in other words, the keys of the kwargs dict. These names must be
     strings (instances of "str" or a subclass) and they must be
     unique. If there are no keyword arguments, then *kwnames* can
     instead be *NULL*.

PY_VECTORCALL_ARGUMENTS_OFFSET

   If this flag is set in a vectorcall *nargsf* argument, the callee
   is allowed to temporarily change "args[-1]". In other words, *args*
   points to argument 1 (not 0) in the allocated vector. The callee
   must restore the value of "args[-1]" before returning.

   For "PyObject_VectorcallMethod()", this flag means instead that
   "args[0]" may be changed.

   Whenever they can do so cheaply (without additional allocation),
   callers are encouraged to use "PY_VECTORCALL_ARGUMENTS_OFFSET".
   Doing so will allow callables such as bound methods to make their
   onward calls (which include a prepended *self* argument) very
   efficiently.

To call an object that implements vectorcall, use a call API function
as with any other callable. "PyObject_Vectorcall()" will usually be
most efficient.

注釈:

  In CPython 3.8, the vectorcall API and related functions were
  available provisionally under names with a leading underscore:
  "_PyObject_Vectorcall", "_Py_TPFLAGS_HAVE_VECTORCALL",
  "_PyObject_VectorcallMethod", "_PyVectorcall_Function",
  "_PyObject_CallOneArg", "_PyObject_CallMethodNoArgs",
  "_PyObject_CallMethodOneArg". Additionally,
  "PyObject_VectorcallDict" was available as "_PyObject_FastCallDict".
  The old names are still defined as aliases of the new, non-
  underscored names.


再帰の管理
----------

When using *tp_call*, callees do not need to worry about recursion:
CPython uses "Py_EnterRecursiveCall()" and "Py_LeaveRecursiveCall()"
for calls made using *tp_call*.

For efficiency, this is not the case for calls done using vectorcall:
the callee should use *Py_EnterRecursiveCall* and
*Py_LeaveRecursiveCall* if needed.


Vectorcall Support API
----------------------

Py_ssize_t PyVectorcall_NARGS(size_t nargsf)

   Given a vectorcall *nargsf* argument, return the actual number of
   arguments. Currently equivalent to:

      (Py_ssize_t)(nargsf & ~PY_VECTORCALL_ARGUMENTS_OFFSET)

   However, the function "PyVectorcall_NARGS" should be used to allow
   for future extensions.

   バージョン 3.8 で追加.

vectorcallfunc PyVectorcall_Function(PyObject *op)

   If *op* does not support the vectorcall protocol (either because
   the type does not or because the specific instance does not),
   return *NULL*. Otherwise, return the vectorcall function pointer
   stored in *op*. This function never raises an exception.

   This is mostly useful to check whether or not *op* supports
   vectorcall, which can be done by checking
   "PyVectorcall_Function(op) != NULL".

   バージョン 3.8 で追加.

PyObject *PyVectorcall_Call(PyObject *callable, PyObject *tuple, PyObject *dict)

   Call *callable*'s "vectorcallfunc" with positional and keyword
   arguments given in a tuple and dict, respectively.

   This is a specialized function, intended to be put in the "tp_call"
   slot or be used in an implementation of "tp_call". It does not
   check the "Py_TPFLAGS_HAVE_VECTORCALL" flag and it does not fall
   back to "tp_call".

   バージョン 3.8 で追加.


Object Calling API
==================

Various functions are available for calling a Python object. Each
converts its arguments to a convention supported by the called object
– either *tp_call* or vectorcall. In order to do as little conversion
as possible, pick one that best fits the format of data you have
available.

The following table summarizes the available functions; please see
individual documentation for details.

+--------------------------------------------+--------------------+----------------------+-----------------+
| 関数                                       | callable           | "args"               | "kwargs"        |
|============================================|====================|======================|=================|
| "PyObject_Call()"                          | "PyObject *"       | tuple                | dict/"NULL"     |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallNoArgs()"                    | "PyObject *"       | ---                  | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallOneArg()"                    | "PyObject *"       | 1 object             | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallObject()"                    | "PyObject *"       | tuple/"NULL"         | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallFunction()"                  | "PyObject *"       | format               | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallMethod()"                    | obj + "char*"      | format               | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallFunctionObjArgs()"           | "PyObject *"       | variadic             | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallMethodObjArgs()"             | obj + name         | variadic             | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallMethodNoArgs()"              | obj + name         | ---                  | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_CallMethodOneArg()"              | obj + name         | 1 object             | ---             |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_Vectorcall()"                    | "PyObject *"       | vectorcall           | vectorcall      |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_VectorcallDict()"                | "PyObject *"       | vectorcall           | dict/"NULL"     |
+--------------------------------------------+--------------------+----------------------+-----------------+
| "PyObject_VectorcallMethod()"              | arg + name         | vectorcall           | vectorcall      |
+--------------------------------------------+--------------------+----------------------+-----------------+

PyObject *PyObject_Call(PyObject *callable, PyObject *args, PyObject *kwargs)
    *Return value: New reference.** Part of the Stable ABI.*

   呼び出し可能な Python のオブジェクト *callable* を、タプル *args*
   として与えられる引数と辞書 *kwargs* として与えられる名前付き引数と
   ともに呼び出します。

   *args* は *NULL* であってはならず、引数を必要としない場合は空のタプ
   ルを使ってください。 *kwargs* は *NULL* でも構いません。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   これは次の Python の式と同等です: "callable(*args, **kwargs)" 。

PyObject *PyObject_CallNoArgs(PyObject *callable)
    * Part of the Stable ABI since version 3.10.*

   Call a callable Python object *callable* without any arguments. It
   is the most efficient way to call a callable Python object without
   any argument.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.

PyObject *PyObject_CallOneArg(PyObject *callable, PyObject *arg)

   Call a callable Python object *callable* with exactly 1 positional
   argument *arg* and no keyword arguments.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.

PyObject *PyObject_CallObject(PyObject *callable, PyObject *args)
    *Return value: New reference.** Part of the Stable ABI.*

   呼び出し可能な Python のオブジェクト *callable* を、タプル *args*
   として与えられる引数とともに呼び出します。 引数が必要な場合は、
   *args* は *NULL* で構いません。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   これは次の Python の式と同等です: "callable(*args)" 。

PyObject *PyObject_CallFunction(PyObject *callable, const char *format, ...)
    *Return value: New reference.** Part of the Stable ABI.*

   呼び出し可能な Python オブジェクト *callable* を可変数個の C 引数と
   ともに呼び出します。 C 引数は "Py_BuildValue()" 形式のフォーマット
   文字列を使って記述します。 *format* は *NULL* かもしれず、与える引
   数がないことを表します。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   これは次の Python の式と同等です: "callable(*args)" 。

   "PyObject*" args だけを引数に渡す場合は、
   "PyObject_CallFunctionObjArgs()" がより速い方法であることを覚えてお
   いてください。

   バージョン 3.4 で変更: *format* の型が "char *" から変更されました
   。

PyObject *PyObject_CallMethod(PyObject *obj, const char *name, const char *format, ...)
    *Return value: New reference.** Part of the Stable ABI.*

   オブジェクト *obj* の *name* という名前のメソッドを、いくつかの C
   引数とともに呼び出します。 C 引数はタプルを生成する
   "Py_BuildValue()" 形式のフォーマット文字列で記述されています。

   *format* は *NULL* でもよく、引数が与えられないことを表します。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   これは次の Python の式と同等です: "obj.name(arg1, arg2, ...)" 。

   "PyObject*" args だけを引数に渡す場合は、
   "PyObject_CallMethodObjArgs()" がより速い方法であることを覚えておい
   てください。

   バージョン 3.4 で変更: *name* と *format* の型が "char *" から変更
   されました。

PyObject *PyObject_CallFunctionObjArgs(PyObject *callable, ...)
    *Return value: New reference.** Part of the Stable ABI.*

   呼び出し可能な Python オブジェクト *callable* を可変数個の
   "PyObject*" 引数とともに呼び出します。引数列は末尾に *NULL* がつい
   た可変数個のパラメタとして与えます。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   これは次の Python の式と同等です: "callable(arg1, arg2, ...)" 。

PyObject *PyObject_CallMethodObjArgs(PyObject *obj, PyObject *name, ...)
    *Return value: New reference.** Part of the Stable ABI.*

   Python オブジェクト *obj* のメソッドを呼び出します、メソッド名は
   Python 文字列オブジェクト *name* で与えます。可変数個の "PyObject*"
   引数と共に呼び出されます. 引数列は末尾に *NULL* がついた可変数個の
   パラメタとして与えます。

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

PyObject *PyObject_CallMethodNoArgs(PyObject *obj, PyObject *name)

   Call a method of the Python object *obj* without arguments, where
   the name of the method is given as a Python string object in
   *name*.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.

PyObject *PyObject_CallMethodOneArg(PyObject *obj, PyObject *name, PyObject *arg)

   Call a method of the Python object *obj* with a single positional
   argument *arg*, where the name of the method is given as a Python
   string object in *name*.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.

PyObject *PyObject_Vectorcall(PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwnames)

   Call a callable Python object *callable*. The arguments are the
   same as for "vectorcallfunc". If *callable* supports vectorcall,
   this directly calls the vectorcall function stored in *callable*.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.

PyObject *PyObject_VectorcallDict(PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwdict)

   Call *callable* with positional arguments passed exactly as in the
   vectorcall protocol, but with keyword arguments passed as a
   dictionary *kwdict*. The *args* array contains only the positional
   arguments.

   Regardless of which protocol is used internally, a conversion of
   arguments needs to be done. Therefore, this function should only be
   used if the caller already has a dictionary ready to use for the
   keyword arguments, but not a tuple for the positional arguments.

   バージョン 3.9 で追加.

PyObject *PyObject_VectorcallMethod(PyObject *name, PyObject *const *args, size_t nargsf, PyObject *kwnames)

   Call a method using the vectorcall calling convention. The name of
   the method is given as a Python string *name*. The object whose
   method is called is *args[0]*, and the *args* array starting at
   *args[1]* represents the arguments of the call. There must be at
   least one positional argument. *nargsf* is the number of positional
   arguments including *args[0]*, plus
   "PY_VECTORCALL_ARGUMENTS_OFFSET" if the value of "args[0]" may
   temporarily be changed. Keyword arguments can be passed just like
   in "PyObject_Vectorcall()".

   If the object has the "Py_TPFLAGS_METHOD_DESCRIPTOR" feature, this
   will call the unbound method object with the full *args* vector as
   arguments.

   成功したら呼び出しの結果を返し、失敗したら例外を送出し *NULL* を返
   します。

   バージョン 3.9 で追加.


Call Support API
================

int PyCallable_Check(PyObject *o)
    * Part of the Stable ABI.*

   オブジェクト *o* が呼び出し可能オブジェクトかどうか調べます。オブジ
   ェクトが呼び出し可能であるときに "1" を返し、そうでないときには "0"
   を返します。この関数呼び出しは常に成功します。
