通用物件結構
************

大量的结构体被用于定义Python的对象类型。这一节描述了这些的结构体和它们
的使用方法。


基本的对象类型和宏
==================

所有的 Python 对象都在对象的内存表示的开始部分共享少量的字段。 这些字
段用 "PyObject" 或 "PyVarObject" 类型来表示，这些类型又由一些宏定义，
这些宏也直接或间接地用于所有其他 Python 对象的定义。

type PyObject
    * Part of the Limited API. (Only some members are part of the
   stable ABI.)*

   所有对象类型都是此类型的扩展。 这是一个包含了 Python 将对象的指针当
   作对象来处理所需的信息的类型。 在一个普通的“发行”编译版中，它只包含
   对象的引用计数和指向对应类型对象的指针。 没有什么对象被实际声明为
   "PyObject"，但每个指向 Python 对象的指针都可以被转换为 "PyObject*"
   。 对成员的访问必须通过使用 "Py_REFCNT" 和 "Py_TYPE" 宏来完成。

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

   这是一个在声明代表无可变长度对象的新类型时所使用的宏。
   PyObject_HEAD 宏被扩展为:

      PyObject ob_base;

   参见上面 "PyObject" 的文档。

PyObject_VAR_HEAD

   这是一个在声明代表每个实例具有可变长度的对象时所使用的宏。
   PyObject_VAR_HEAD 宏被扩展为:

      PyVarObject ob_base;

   参见上面 "PyVarObject" 的文档。

int Py_Is(const PyObject *x, const PyObject *y)
    * Part of the Stable ABI since version 3.10.*

   测试 *x* 是否为 *y* 对象，与 Python 中的 "x is y" 相同。

   3.10 版新加入.

int Py_IsNone(const PyObject *x)
    * Part of the Stable ABI since version 3.10.*

   测试一个对象是否为 "None" 单例，与 Python 中的 "x is None" 相同。

   3.10 版新加入.

int Py_IsTrue(const PyObject *x)
    * Part of the Stable ABI since version 3.10.*

   测试一个对象是否为 "True" 单例，与 Python 中的 "x is True" 相同。

   3.10 版新加入.

int Py_IsFalse(const PyObject *x)
    * Part of the Stable ABI since version 3.10.*

   测试一个对象是否为 "False" 单例，与 Python 中的 "x is False" 相同。

   3.10 版新加入.

PyTypeObject *Py_TYPE(const PyObject *o)

   获取 Python 对象 *o* 的类型。

   返回一个 *borrowed reference*。

   使用 "Py_SET_TYPE()" 函数来设置一个对象类型。

int Py_IS_TYPE(PyObject *o, PyTypeObject *type)

   如果对象 *o* 的类型为 *type* 则返回非零值。 否则返回零。 等价于:
   "Py_TYPE(o) == type"。

   3.9 版新加入.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

   将对象 *o* 的类型设为 *type*。

   3.9 版新加入.

Py_ssize_t Py_REFCNT(const PyObject *o)

   获取 Python 对象 *o* 的引用计数。

   3.10 版更變: "Py_REFCNT()" is changed to the inline static
   function. Use "Py_SET_REFCNT()" to set an object reference count.

void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)

   将对象 *o* 的引用计数器设为 *refcnt*。

   3.9 版新加入.

Py_ssize_t Py_SIZE(const PyVarObject *o)

   获取 Python 对象 *o* 的大小。

   使用 "Py_SET_SIZE()" 函数来设置一个对象大小。

void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)

   将对象 *o* 的大小设为 *size*。

   3.9 版新加入.

PyObject_HEAD_INIT(type)

   这是一个为新的 "PyObject" 类型扩展初始化值的宏。 该宏扩展为:

      _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,


实现函数和方法
==============

type PyCFunction
    * Part of the Stable ABI.*

   用于在 C 中实现大多数 Python 可调用对象的函数类型。 该类型的函数接
   受两个 "PyObject*" 形参并返回一个这样的值。 如果返回值为 "NULL"，则
   将设置一个异常。 如果不为 "NULL"，则返回值将被解读为 Python 中暴露
   的函数的返回值。 此函数必须返回一个新的引用。

   函数的签名为:

      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)

   3.9 版新加入.

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

   用于描述一个扩展类型的方法的结构体。 该结构体有四个字段:

   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.

调用惯例有如下这些:

METH_VARARGS

   这是典型的调用惯例，其中方法的类型为 "PyCFunction"。 该函数接受两个
   "PyObject*" 值。 第一个是用于方法的 *self* 对象；对于模块函数，它将
   为模块对象。 第二个形参 (常被命名为 *args*) 是一个代表所有参数的元
   组对象。 该形参通常是使用 "PyArg_ParseTuple()" 或
   "PyArg_UnpackTuple()" 来处理的。

METH_VARARGS | METH_KEYWORDS

   带有这些旗标的方法必须为 "PyCFunctionWithKeywords" 类型。 该函数接
   受三个形参: *self*, *args*, *kwargs* 其中 *kwargs* 是一个包含所有关
   键字参数的字典或者如果没有关键字参数则可以为 "NULL"。 这些形参通常
   是使用 "PyArg_ParseTupleAndKeywords()" 来处理的。

METH_FASTCALL

   快速调用惯例仅支持位置参数。 这些方法的类型为 "_PyCFunctionFast"。
   第一个形参为 *self*，第二个形参是由表示参数的 "PyObject*" 值组成的
   数组而第三个形参是参数的数量（数组的长度）。

   3.7 版新加入.

   3.10 版更變: "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.

   3.7 版新加入.

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)".

   该方法必须为 "PyCMethod" 类型，与在 "self" 之后添加了
   "defining_class" 参数的 "METH_FASTCALL | METH_KEYWORDS" 一样。

   3.9 版新加入.

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".

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.

这两个常量不是被用来指明调用惯例而是在配合类方法使用时指明绑定。 它们
不会被用于在模块上定义的函数。 对于任何给定方法这些旗标最多只会设置其
中一个。

METH_CLASS

   该方法将接受类型对象而不是类型的实例作为第一个形参。 它会被用于创建
   *类方法*，类似于使用 "classmethod()" 内置函数所创建的结果。

METH_STATIC

   该方法将接受 "NULL" 而不是类型的实例作为第一个形参。 它会被用于创建
   *静态方法*，类似于使用 "staticmethod()" 内置函数所创建的结果。

另一个常量控制方法是否将被载入来替代具有相同方法名的另一个定义。

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.


访问扩展类型的属性
==================

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:

   +--------------------+-----------------+---------------------------------+
   | 域                 | C Type          | 含意                            |
   |====================|=================|=================================|
   | "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.

   +-----------------+--------------------+
   | 宏名称          | C 类型             |
   |=================|====================|
   | 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)

   获取属于地址Get an attribute belonging to the object at address
   *obj_addr* 上的对象的某个属性。 该属性是以 "PyMemberDef" *m* 来描述
   的。 出错时返回 "NULL"。

int PyMember_SetOne(char *obj_addr, struct PyMemberDef *m, PyObject *o)

   将属于位于地址 *obj_addr* 的对象的属性设置到对象 *o*。 要设置的属性
   由 "PyMemberDef" *m* 描述。 成功时返回 "0" 而失败时返回负值。

type PyGetSetDef
    * Part of the Stable ABI (including all members).*

   用于定义针对某个类型的特征属性式的访问的结构体。 另请参阅
   "PyTypeObject.tp_getset" 槽位的描述。

   +---------------+--------------------+-------------------------------------+
   | 域            | C Type             | 含意                                |
   |===============|====================|=====================================|
   | name          | const char *       | 属性名称                            |
   +---------------+--------------------+-------------------------------------+
   | 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 *       | 可选的文档字符串                    |
   +---------------+--------------------+-------------------------------------+
   | closure       | void *             | optional function pointer,          |
   |               |                    | providing additional data for       |
   |               |                    | getter and setter                   |
   +---------------+--------------------+-------------------------------------+

   "get" 函数接受一个 "PyObject*" 形参 (实例) 和一个函数指针 (关联的
   "closure"):

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

   它应当在成功时返回一个新的引用或在失败时返回 "NULL" 并设置异常。

   "set" 函数接受两个 "PyObject*" 形参 (实例和要设置的值) 和一个函数指
   针 (关联的 "closure"):

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

   对于属性要被删除的情况第二个形参应为 "NULL"。 成功时应返回 "0" 或在
   失败时返回 "-1" 并设置异常。
