# 공통 객체 구조체

파이썬의 객체 형 정의에 사용되는 많은 구조체가 있습니다. 이 섹션에서는 이러한 구조체와 사용 방법에 관해 설명합니다.

## 기본 객체 형과 매크로

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 제한된 API. (Only some members are part of the stable ABI.)

  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*. Access to the members must be done by using the macros `Py_REFCNT` and `Py_TYPE`.

type PyVarObject
  Part of the 제한된 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

  길이가 변하지 않는 객체를 나타내는 새로운 형을 선언할 때 사용되는 매크로입니다. PyObject_HEAD 매크로는 다음과 같이 확장됩니다:

      PyObject ob_base;

  위의 `PyObject` 설명서를 참조하십시오.

PyObject_VAR_HEAD

  인스턴스마다 길이가 다른 객체를 나타내는 새로운 형을 선언할 때 사용되는 매크로입니다. PyObject_VAR_HEAD 매크로는 다음과 같이 확장됩니다:

      PyVarObject ob_base;

  위의 `PyVarObject` 설명서를 참조하십시오.

int Py_Is(PyObject *x, PyObject *y)
  Part of the 안정 ABI 버전 3.10 이후로.

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

  버전 3.10에 추가.

int Py_IsNone(PyObject *x)
  Part of the 안정 ABI 버전 3.10 이후로.

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

  버전 3.10에 추가.

int Py_IsTrue(PyObject *x)
  Part of the 안정 ABI 버전 3.10 이후로.

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

  버전 3.10에 추가.

int Py_IsFalse(PyObject *x)
  Part of the 안정 ABI 버전 3.10 이후로.

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

  버전 3.10에 추가.

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.

  버전 3.11에서 변경: `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)

  객체 o의 형이 type이면 0이 아닌 값을 반환합니다. 그렇지 않으면 0을 반환합니다. `Py_TYPE(o) == type`과 동등합니다.

  버전 3.9에 추가.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

  객체 o의 형을 type으로 설정합니다.

  버전 3.9에 추가.

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.

  버전 3.11에서 변경: The parameter type is no longer const PyObject*.

  버전 3.10에서 변경: `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.

  버전 3.9에 추가.

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.

  버전 3.11에서 변경: `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)

  객체 o의 크기를 size로 설정합니다.

  버전 3.9에 추가.

PyObject_HEAD_INIT(type)

  이것은 새로운 `PyObject` 형의 초기화 값으로 확장되는 매크로입니다. 이 매크로는 다음으로 확장됩니다:

      _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,

## 함수와 메서드 구현

type PyCFunction
  Part of the 안정 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.

  함수 서명은 다음과 같습니다:

      PyObject *PyCFunction(PyObject *self,
                            PyObject *args);

type PyCFunctionWithKeywords
  Part of the 안정 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)

  버전 3.9에 추가.

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

  확장형의 메서드를 기술하는 데 사용되는 구조체. 이 구조체에는 네 개의 필드가 있습니다:

  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.

다음과 같은 호출 규칙이 있습니다:

METH_VARARGS

  This is the typical calling convention, where the methods have the type `PyCFunction`. The function expects two PyObject* values. The first one is the self object for methods; for module functions, it is the module object. The second parameter (often called args) is a tuple object representing all arguments. This parameter is typically processed using `PyArg_ParseTuple()` or `PyArg_UnpackTuple()`.

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

  이러한 플래그가 있는 메서드는 `PyCFunctionWithKeywords` 형이어야 합니다. 이 함수는 세 개의 매개 변수를 기대합니다: self, args, kwargs. 여기서 kwargs는 모든 키워드 인자의 딕셔너리이거나 키워드 인자가 없으면 `NULL`일 수 있습니다. 매개 변수는 일반적으로 `PyArg_ParseTupleAndKeywords()`를 사용하여 처리됩니다.

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).

  버전 3.7에 추가.

  버전 3.10에서 변경: `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.

  버전 3.7에 추가.

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)`.

  메서드는 `PyCMethod` 형이어야 하는데, `self` 뒤에 `defining_class` 인자가 추가된 `METH_FASTCALL | METH_KEYWORDS`와 같습니다.

  버전 3.9에 추가.

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.

이 두 상수는 호출 규칙을 나타내는 데 사용되지 않고 클래스의 메서드와 함께 사용할 때 바인딩을 나타냅니다. 모듈에 정의된 함수에는 사용할 수 없습니다. 이러한 플래그 중 최대 하나를 주어진 메서드에 대해 설정할 수 있습니다.

METH_CLASS

  메서드로 형의 인스턴스가 아닌 형 객체가 첫 번째 매개 변수로 전달됩니다. `classmethod()` 내장 함수를 사용할 때 만들어지는 것과 유사한 클래스 메서드(class methods)를 만드는 데 사용됩니다.

METH_STATIC

  메서드로 형의 인스턴스가 아닌 `NULL`이 첫 번째 매개 변수로 전달됩니다. `staticmethod()` 내장 함수를 사용할 때 만들어지는 것과 유사한 정적 메서드(static methods)를 만드는 데 사용됩니다.

하나의 다른 상수는 같은 메서드 이름을 가진 다른 정의 대신 메서드가 로드되는지를 제어합니다.

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)
  반환값: 새 참조. Part of the 안정 ABI 버전 3.9 이후로.

  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`.

  더 보기

  `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`.

  버전 3.9에 추가.

PyObject *PyCFunction_NewEx(PyMethodDef *ml, PyObject *self, PyObject *module)
  반환값: 새 참조. Part of the 안정 ABI.

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

PyObject *PyCFunction_New(PyMethodDef *ml, PyObject *self)
  반환값: 새 참조. Part of the 안정 ABI 버전 3.4 이후로.

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

## 확장형의 어트리뷰트 액세스

type PyMemberDef
  Part of the 안정 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.

  매크로 이름 | C 형
  --- | ---
  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 안정 ABI (including all members).

  형에 대한 프로퍼티 같은 액세스를 정의하는 구조체. `PyTypeObject.tp_getset` 슬롯에 대한 설명도 참조하십시오.

  Field | C Type | Meaning
  --- | --- | ---
  name | const char * | 어트리뷰트 이름
  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 * | 선택적 독스트링
  closure | void * | optional user data pointer, providing additional data for getter and setter

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

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

  성공하면 새 참조를 반환하고, 실패하면 설정된 예외와 함께 `NULL`을 반환해야 합니다.

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

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

  어트리뷰트를 삭제해야 하는 경우 두 번째 매개 변수는 `NULL`입니다. 성공하면 `0`을, 실패하면 설정된 예외와 함께 `-1`을 반환해야 합니다.