类型对象
********

也许 Python 对象系统中最重要的结构之一就是定义新类型的结构:
"PyTypeObject" 结构。 类型对象可以使用任何 "PyObject_*()" 或
"PyType_*()" 函数来处理，但不能提供大多数 Python 应用程序所感兴趣的内
容。 这些对象是对象行为的基础，所以它们对解释器本身或任何实现新类型的
扩展模块都非常重要。

与大多数标准类型相比，类型对象相当大。这么大的原因是每个类型对象存储了
大量的值，大部分是C函数指针，每个指针实现了类型功能的一小部分。本节将
详细描述类型对象的字段。这些字段将按照它们在结构中出现的顺序进行描述。

除了下面的快速参考， 例子 小节提供了快速了解 "PyTypeObject" 的含义和用
法的例子。


快速参考
========


"tp_方法槽"
-----------

+--------------------+--------------------+--------------------+----+----+----+----+
| PyTypeObject 槽    | Type               | 特殊方法/属性      | 信息 [2]          |
| [1]                |                    |                    |                   |
|                    |                    |                    +----+----+----+----+
|                    |                    |                    | O  | T  | D  | I  |
|                    |                    |                    |    |    |    |    |
|====================|====================|====================|====|====|====|====|
| <R> "tp_name"      | const char *       | __name__           | X  | X  |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_basicsize"     | Py_ssize_t         |                    | X  | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_itemsize"      | Py_ssize_t         |                    |    | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_dealloc"       | "destructor"       |                    | X  | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_vectorcall_of  | Py_ssize_t         |                    |    |    |    | ?  |
| fset"              |                    |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| ("tp_getattr")     | "getattrfunc"      | __getattribute__,  |    |    |    | G  |
|                    |                    | __getattr__        |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| ("tp_setattr")     | "setattrfunc"      | __setattr__,       |    |    |    | G  |
|                    |                    | __delattr__        |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_as_async"      | "PyAsyncMethods" * | 子方法槽（方法域） |    |    |    | %  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_repr"          | "reprfunc"         | __repr__           | X  | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_as_number"     | "PyNumberMethods"  | 子方法槽（方法域） |    |    |    | %  |
|                    | *                  |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_as_sequence"   | "PySequenceMethod  | 子方法槽（方法域） |    |    |    | %  |
|                    | s" *               |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_as_mapping"    | "PyMappingMethods" | 子方法槽（方法域） |    |    |    | %  |
|                    | *                  |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_hash"          | "hashfunc"         | __hash__           | X  |    |    | G  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_call"          | "ternaryfunc"      | __call__           |    | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_str"           | "reprfunc"         | __str__            | X  |    |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_getattro"      | "getattrofunc"     | __getattribute__,  | X  | X  |    | G  |
|                    |                    | __getattr__        |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_setattro"      | "setattrofunc"     | __setattr__,       | X  | X  |    | G  |
|                    |                    | __delattr__        |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_as_buffer"     | "PyBufferProcs" *  |                    |    |    |    | %  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_flags"         | unsigned long      |                    | X  | X  |    | ?  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_doc"           | const char *       | __doc__            | X  | X  |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_traverse"      | "traverseproc"     |                    |    | X  |    | G  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_clear"         | "inquiry"          |                    |    | X  |    | G  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_richcompare"   | "richcmpfunc"      | __lt__, __le__,    | X  |    |    | G  |
|                    |                    | __eq__, __ne__,    |    |    |    |    |
|                    |                    | __gt__, __ge__     |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_weaklistoffse  | Py_ssize_t         |                    |    | X  |    | ?  |
| t"                 |                    |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_iter"          | "getiterfunc"      | __iter__           |    |    |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_iternext"      | "iternextfunc"     | __next__           |    |    |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_methods"       | "PyMethodDef" []   |                    | X  | X  |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_members"       | "PyMemberDef" []   |                    |    | X  |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_getset"        | "PyGetSetDef" []   |                    | X  | X  |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_base"          | "PyTypeObject" *   | __base__           |    |    | X  |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_dict"          | "PyObject" *       | __dict__           |    |    | ?  |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_descr_get"     | "descrgetfunc"     | __get__            |    |    |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_descr_set"     | "descrsetfunc"     | __set__,           |    |    |    | X  |
|                    |                    | __delete__         |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_dictoffset"    | Py_ssize_t         |                    |    | X  |    | ?  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_init"          | "initproc"         | __init__           | X  | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_alloc"         | "allocfunc"        |                    | X  |    | ?  | ?  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_new"           | "newfunc"          | __new__            | X  | X  | ?  | ?  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_free"          | "freefunc"         |                    | X  | X  | ?  | ?  |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_is_gc"         | "inquiry"          |                    |    | X  |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+
| <"tp_bases">       | "PyObject" *       | __bases__          |    |    | ~  |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| <"tp_mro">         | "PyObject" *       | __mro__            |    |    | ~  |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| ["tp_cache"]       | "PyObject" *       |                    |    |    |         |
+--------------------+--------------------+--------------------+----+----+----+----+
| ["tp_subclasses"]  | "PyObject" *       | __subclasses__     |    |    |         |
+--------------------+--------------------+--------------------+----+----+----+----+
| ["tp_weaklist"]    | "PyObject" *       |                    |    |    |         |
+--------------------+--------------------+--------------------+----+----+----+----+
| ("tp_del")         | "destructor"       |                    |    |    |    |    |
+--------------------+--------------------+--------------------+----+----+----+----+
| ["tp_version_tag"] | unsigned int       |                    |    |    |         |
+--------------------+--------------------+--------------------+----+----+----+----+
| "tp_finalize"      | "destructor"       | __del__            |    |    |    | X  |
+--------------------+--------------------+--------------------+----+----+----+----+

如果定义了 "COUNT_ALLOCS" ，则还存在以下（仅内部）字段：

* "tp_allocs"

* "tp_frees"

* "tp_maxalloc"

* "tp_prev"

* "tp_next"

[1] 小括号中的槽名表示它(实际上)已弃用。尖括号中的名称应该被视为只读的
    。方括号中的名称仅供内部使用。"<R>"(作为前缀)表示该字段是必需的(必
    须是非null)。

[2] 列：

    **"O"**:  "PyBaseObject_Type" 必须设置

    **"T"**: "PyType_Type" 必须设置

    **"D"**: 默认设置(如果方法槽被设置为NULL)

       X - PyType_Ready sets this value if it is NULL
       ~ - PyType_Ready always sets this value (it should be NULL)
       ? - PyType_Ready may set this value depending on other slots

       Also see the inheritance column ("I").

    **"I"**: 继承

       X - type slot is inherited via PyType_Ready if defined with a NULL value
       % - the slots of the sub-struct are inherited individually
       G - inherited, but only in combination with other slots; see the slot's description
       ? - it's complicated; see the slot's description

    注意，有些方法槽是通过普通属性查找链有效继承的。


子方法槽（方法域）
------------------

+----------------------------+-------------------+--------------+
| 方法槽                     | Type              | 特殊方法     |
|============================|===================|==============|
| "am_await"                 | "unaryfunc"       | __await__    |
+----------------------------+-------------------+--------------+
| "am_aiter"                 | "unaryfunc"       | __aiter__    |
+----------------------------+-------------------+--------------+
| "am_anext"                 | "unaryfunc"       | __anext__    |
+----------------------------+-------------------+--------------+
|                                                               |
+----------------------------+-------------------+--------------+
| "nb_add"                   | "binaryfunc"      | __add__      |
|                            |                   | __radd__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_add"           | "binaryfunc"      | __iadd__     |
+----------------------------+-------------------+--------------+
| "nb_subtract"              | "binaryfunc"      | __sub__      |
|                            |                   | __rsub__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_subtract"      | "binaryfunc"      | __sub__      |
+----------------------------+-------------------+--------------+
| "nb_multiply"              | "binaryfunc"      | __mul__      |
|                            |                   | __rmul__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_multiply"      | "binaryfunc"      | __mul__      |
+----------------------------+-------------------+--------------+
| "nb_remainder"             | "binaryfunc"      | __mod__      |
|                            |                   | __rmod__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_remainder"     | "binaryfunc"      | __mod__      |
+----------------------------+-------------------+--------------+
| "nb_divmod"                | "binaryfunc"      | __divmod__   |
|                            |                   | __rdivmod__  |
+----------------------------+-------------------+--------------+
| "nb_power"                 | "ternaryfunc"     | __pow__      |
|                            |                   | __rpow__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_power"         | "ternaryfunc"     | __pow__      |
+----------------------------+-------------------+--------------+
| "nb_negative"              | "unaryfunc"       | __neg__      |
+----------------------------+-------------------+--------------+
| "nb_positive"              | "unaryfunc"       | __pos__      |
+----------------------------+-------------------+--------------+
| "nb_absolute"              | "unaryfunc"       | __abs__      |
+----------------------------+-------------------+--------------+
| "nb_bool"                  | "inquiry"         | __bool__     |
+----------------------------+-------------------+--------------+
| "nb_invert"                | "unaryfunc"       | __invert__   |
+----------------------------+-------------------+--------------+
| "nb_lshift"                | "binaryfunc"      | __lshift__   |
|                            |                   | __rlshift__  |
+----------------------------+-------------------+--------------+
| "nb_inplace_lshift"        | "binaryfunc"      | __lshift__   |
+----------------------------+-------------------+--------------+
| "nb_rshift"                | "binaryfunc"      | __rshift__   |
|                            |                   | __rrshift__  |
+----------------------------+-------------------+--------------+
| "nb_inplace_rshift"        | "binaryfunc"      | __rshift__   |
+----------------------------+-------------------+--------------+
| "nb_and"                   | "binaryfunc"      | __and__      |
|                            |                   | __rand__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_and"           | "binaryfunc"      | __and__      |
+----------------------------+-------------------+--------------+
| "nb_xor"                   | "binaryfunc"      | __xor__      |
|                            |                   | __rxor__     |
+----------------------------+-------------------+--------------+
| "nb_inplace_xor"           | "binaryfunc"      | __xor__      |
+----------------------------+-------------------+--------------+
| "nb_or"                    | "binaryfunc"      | __or__       |
|                            |                   | __ror__      |
+----------------------------+-------------------+--------------+
| "nb_inplace_or"            | "binaryfunc"      | __or__       |
+----------------------------+-------------------+--------------+
| "nb_int"                   | "unaryfunc"       | __int__      |
+----------------------------+-------------------+--------------+
| "nb_reserved"              | void *            |              |
+----------------------------+-------------------+--------------+
| "nb_float"                 | "unaryfunc"       | __float__    |
+----------------------------+-------------------+--------------+
| "nb_floor_divide"          | "binaryfunc"      | __floordiv__ |
+----------------------------+-------------------+--------------+
| "nb_inplace_floor_divide"  | "binaryfunc"      | __floordiv__ |
+----------------------------+-------------------+--------------+
| "nb_true_divide"           | "binaryfunc"      | __truediv__  |
+----------------------------+-------------------+--------------+
| "nb_inplace_true_divide"   | "binaryfunc"      | __truediv__  |
+----------------------------+-------------------+--------------+
| "nb_index"                 | "unaryfunc"       | __index__    |
+----------------------------+-------------------+--------------+
| "nb_matrix_multiply"       | "binaryfunc"      | __matmul__   |
|                            |                   | __rmatmul__  |
+----------------------------+-------------------+--------------+
| "nb_inplace_matrix_multip  | "binaryfunc"      | __matmul__   |
| ly"                        |                   |              |
+----------------------------+-------------------+--------------+
|                                                               |
+----------------------------+-------------------+--------------+
| "mp_length"                | "lenfunc"         | __len__      |
+----------------------------+-------------------+--------------+
| "mp_subscript"             | "binaryfunc"      | __getitem__  |
+----------------------------+-------------------+--------------+
| "mp_ass_subscript"         | "objobjargproc"   | __setitem__, |
|                            |                   | __delitem__  |
+----------------------------+-------------------+--------------+
|                                                               |
+----------------------------+-------------------+--------------+
| "sq_length"                | "lenfunc"         | __len__      |
+----------------------------+-------------------+--------------+
| "sq_concat"                | "binaryfunc"      | __add__      |
+----------------------------+-------------------+--------------+
| "sq_repeat"                | "ssizeargfunc"    | __mul__      |
+----------------------------+-------------------+--------------+
| "sq_item"                  | "ssizeargfunc"    | __getitem__  |
+----------------------------+-------------------+--------------+
| "sq_ass_item"              | "ssizeobjargproc" | __setitem__  |
|                            |                   | __delitem__  |
+----------------------------+-------------------+--------------+
| "sq_contains"              | "objobjproc"      | __contains__ |
+----------------------------+-------------------+--------------+
| "sq_inplace_concat"        | "binaryfunc"      | __iadd__     |
+----------------------------+-------------------+--------------+
| "sq_inplace_repeat"        | "ssizeargfunc"    | __imul__     |
+----------------------------+-------------------+--------------+
|                                                               |
+----------------------------+-------------------+--------------+
| "bf_getbuffer"             | "getbufferproc()" |              |
+----------------------------+-------------------+--------------+
| "bf_releasebuffer"         | "releasebufferpr  |              |
|                            | oc()"             |              |
+----------------------------+-------------------+--------------+


槽位 typedef
------------

+-------------------------------+-------------------------------+------------------------+
| typedef                       | 参数类型                      | 返回类型               |
|===============================|===============================|========================|
| "allocfunc"                   | "PyTypeObject" * Py_ssize_t   | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "destructor"                  | void *                        | void                   |
+-------------------------------+-------------------------------+------------------------+
| "freefunc"                    | void *                        | void                   |
+-------------------------------+-------------------------------+------------------------+
| "traverseproc"                | void * "visitproc" void *     | int                    |
+-------------------------------+-------------------------------+------------------------+
| "newfunc"                     | "PyObject" * "PyObject" *     | "PyObject" *           |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "initproc"                    | "PyObject" * "PyObject" *     | int                    |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "reprfunc"                    | "PyObject" *                  | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "getattrfunc"                 | "PyObject" * const char *     | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "setattrfunc"                 | "PyObject" * const char *     | int                    |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "getattrofunc"                | "PyObject" * "PyObject" *     | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "setattrofunc"                | "PyObject" * "PyObject" *     | int                    |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "descrgetfunc"                | "PyObject" * "PyObject" *     | "PyObject" *           |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "descrsetfunc"                | "PyObject" * "PyObject" *     | int                    |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "hashfunc"                    | "PyObject" *                  | Py_hash_t              |
+-------------------------------+-------------------------------+------------------------+
| "richcmpfunc"                 | "PyObject" * "PyObject" * int | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "getiterfunc"                 | "PyObject" *                  | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "iternextfunc"                | "PyObject" *                  | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "lenfunc"                     | "PyObject" *                  | Py_ssize_t             |
+-------------------------------+-------------------------------+------------------------+
| "getbufferproc"               | "PyObject" * "Py_buffer" *    | int                    |
|                               | int                           |                        |
+-------------------------------+-------------------------------+------------------------+
| "releasebufferproc"           | "PyObject" * "Py_buffer" *    | void                   |
+-------------------------------+-------------------------------+------------------------+
| "inquiry"                     | void *                        | int                    |
+-------------------------------+-------------------------------+------------------------+
| "unaryfunc"                   | "PyObject" *                  | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "binaryfunc"                  | "PyObject" * "PyObject" *     | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "ternaryfunc"                 | "PyObject" * "PyObject" *     | "PyObject" *           |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+
| "ssizeargfunc"                | "PyObject" * Py_ssize_t       | "PyObject" *           |
+-------------------------------+-------------------------------+------------------------+
| "ssizeobjargproc"             | "PyObject" * Py_ssize_t       | int                    |
+-------------------------------+-------------------------------+------------------------+
| "objobjproc"                  | "PyObject" * "PyObject" *     | int                    |
+-------------------------------+-------------------------------+------------------------+
| "objobjargproc"               | "PyObject" * "PyObject" *     | int                    |
|                               | "PyObject" *                  |                        |
+-------------------------------+-------------------------------+------------------------+

请参阅 槽位类型 typedef 里有更多详细信息。


PyTypeObject 定义
=================

"PyTypeObject" 的结构定义可以在 "Include/object.h" 中找到。 为了方便参
考，此处复述了其中的定义:

   typedef struct _typeobject {
       PyObject_VAR_HEAD
       const char *tp_name; /* For printing, in format "<module>.<name>" */
       Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

       /* Methods to implement standard operations */

       destructor tp_dealloc;
       Py_ssize_t tp_vectorcall_offset;
       getattrfunc tp_getattr;
       setattrfunc tp_setattr;
       PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                       or tp_reserved (Python 3) */
       reprfunc tp_repr;

       /* Method suites for standard classes */

       PyNumberMethods *tp_as_number;
       PySequenceMethods *tp_as_sequence;
       PyMappingMethods *tp_as_mapping;

       /* More standard operations (here for binary compatibility) */

       hashfunc tp_hash;
       ternaryfunc tp_call;
       reprfunc tp_str;
       getattrofunc tp_getattro;
       setattrofunc tp_setattro;

       /* Functions to access object as input/output buffer */
       PyBufferProcs *tp_as_buffer;

       /* Flags to define presence of optional/expanded features */
       unsigned long tp_flags;

       const char *tp_doc; /* Documentation string */

       /* call function for all accessible objects */
       traverseproc tp_traverse;

       /* delete references to contained objects */
       inquiry tp_clear;

       /* rich comparisons */
       richcmpfunc tp_richcompare;

       /* weak reference enabler */
       Py_ssize_t tp_weaklistoffset;

       /* Iterators */
       getiterfunc tp_iter;
       iternextfunc tp_iternext;

       /* Attribute descriptor and subclassing stuff */
       struct PyMethodDef *tp_methods;
       struct PyMemberDef *tp_members;
       struct PyGetSetDef *tp_getset;
       struct _typeobject *tp_base;
       PyObject *tp_dict;
       descrgetfunc tp_descr_get;
       descrsetfunc tp_descr_set;
       Py_ssize_t tp_dictoffset;
       initproc tp_init;
       allocfunc tp_alloc;
       newfunc tp_new;
       freefunc tp_free; /* Low-level free-memory routine */
       inquiry tp_is_gc; /* For PyObject_IS_GC */
       PyObject *tp_bases;
       PyObject *tp_mro; /* method resolution order */
       PyObject *tp_cache;
       PyObject *tp_subclasses;
       PyObject *tp_weaklist;
       destructor tp_del;

       /* Type attribute cache version tag. Added in version 2.6 */
       unsigned int tp_version_tag;

       destructor tp_finalize;

   } PyTypeObject;


PyObject 槽位
=============

type 对象结构扩展了 "PyVarObject" 结构。 "ob_size" 字段用于动态类型 (
由 "type_new()" 创建，通常通过 class 语句来调用)。 注意 "PyType_Type"
(元类型) 会初始化 "tp_itemsize"，这意味着它的实例 (即 type 对象) *必须
* 具有 "ob_size" 字段。

PyObject* PyObject._ob_next
PyObject* PyObject._ob_prev

   These fields are only present when the macro "Py_TRACE_REFS" is
   defined. Their initialization to "NULL" is taken care of by the
   "PyObject_HEAD_INIT" macro.  For statically allocated objects,
   these fields always remain "NULL". For dynamically allocated
   objects, these two fields are used to link the object into a
   doubly-linked list of *all* live objects on the heap.  This could
   be used for various debugging purposes; currently the only use is
   to print the objects that are still alive at the end of a run when
   the environment variable "PYTHONDUMPREFS" is set.

   **继承：**

   这些字段不会被子类型继承。

Py_ssize_t PyObject.ob_refcnt

   这是类型对象的引用计数，由 "PyObject_HEAD_INIT" 宏初始化为 "1"。 请
   注意对于静态分配的类型对象 (对象的 "ob_type" 指回该类型) *不会* 被
   加入引用计数。 但对于动态分配的类型对象，实例 *确实* 会被算作引用。

   **继承：**

   子类型不继承此字段。

PyTypeObject* PyObject.ob_type

   这是类型的类型，换句话说就是元类型，它由宏 "PyObject_HEAD_INIT" 的
   参数来做初始化，它的值一般情况下是 "&PyType_Type" 。可是为了使动态
   可载入扩展模块至少在Windows上可用，编译器会报错这是一个不可用的初始
   化。因此按照惯例传递 "NULL" 给宏 "PyObject_HEAD_INIT" 并且在模块的
   初始化函数开始时候其他任何操作之前初始化这个字段。典型做法是这样的
   ：

      Foo_Type.ob_type = &PyType_Type;

   这应该在创建该类型的任何实例之前完成。"PyType_Ready()" 检查
   "ob_type" 是否为 "NULL"，如果是，则用基类的 "ob_type" 字段初始化它
   。如果该字段非零，则 "PyType_Ready()" 不会更改它。

   **继承：**

   此字段会被子类型继承。


PyVarObject 槽位
================

Py_ssize_t PyVarObject.ob_size

   For statically allocated type objects, this should be initialized
   to zero.  For dynamically allocated type objects, this field has a
   special internal meaning.

   **继承：**

   子类型不继承此字段。


PyTypeObject 槽
===============

每个槽位都有一个部分来描述继承关系。如果 "PyType_Ready()" 会在该字段为
"NULL" 时设置它的值，那么也会有一个“默认”部分。（注意，在
"PyBaseObject_Type" 和 "PyType_Type" 中设置的许多字段实际上就是默认值
。）

const char* PyTypeObject.tp_name

   指针，指向以 NULL 结尾的表示类型名称的字符串。对于可以作为模块的全
   局变量访问的类型，字符串应该是完整的模块名，后跟一个点，再后跟类型
   名。对于内置类型，字符串应该只是类型名。如果模块是包的子模块，则完
   整的包名是完整的模块名的一部分。例如，包 "P" 的子包 "Q" 的模块 "M"
   中定义的类型 "T" 的 "tp_name" 应该初始化为 ""P.Q.M.T""。

   For dynamically allocated type objects, this should just be the
   type name, and the module name explicitly stored in the type dict
   as the value for key "'__module__'".

   For statically allocated type objects, the tp_name field should
   contain a dot. Everything before the last dot is made accessible as
   the "__module__" attribute, and everything after the last dot is
   made accessible as the "__name__" attribute.

   如果不存在点号，则整个 "tp_name" 字段将作为 "__name__" 属性访问，而
   "__module__" 属性则将是未定义的（除非在字典中显式地设置，如上文所述
   ）。 这意味着你的类型将无法执行 pickle。 此外，用 pydoc 创建的模块
   文档中也不会列出该类型。

   该字段不可为 "NULL"。 它是 "PyTypeObject()" 中唯一的必填字段（除了
   潜在的 "tp_itemsize" 以外）。

   **继承：**

   子类型不继承此字段。

Py_ssize_t PyTypeObject.tp_basicsize
Py_ssize_t PyTypeObject.tp_itemsize

   通过这些字段可以计算出该类型实例以字节为单位的大小。

   存在两种类型：具有固定长度实例的类型其 "tp_itemsize" 字段为零；具有
   可变长度实例的类型其 "tp_itemsize" 字段不为零。 对于具有固定长度实
   例的类型，所有实例的大小都相同，具体大小由 "tp_basicsize" 给出。

   For a type with variable-length instances, the instances must have
   an "ob_size" field, and the instance size is "tp_basicsize" plus N
   times "tp_itemsize", where N is the "length" of the object.  The
   value of N is typically stored in the instance's "ob_size" field.
   There are exceptions:  for example, ints use a negative "ob_size"
   to indicate a negative number, and N is "abs(ob_size)" there.
   Also, the presence of an "ob_size" field in the instance layout
   doesn't mean that the instance structure is variable-length (for
   example, the structure for the list type has fixed-length
   instances, yet those instances have a meaningful "ob_size" field).

   The basic size includes the fields in the instance declared by the
   macro "PyObject_HEAD" or "PyObject_VAR_HEAD" (whichever is used to
   declare the instance struct) and this in turn includes the
   "_ob_prev" and "_ob_next" fields if they are present.  This means
   that the only correct way to get an initializer for the
   "tp_basicsize" is to use the "sizeof" operator on the struct used
   to declare the instance layout. The basic size does not include the
   GC header size.

   关于对齐的说明：如果变量条目需要特定的对齐，则应通过 "tp_basicsize"
   的值来处理。 例如：假设某个类型实现了一个 "double" 数组。
   "tp_itemsize" 就是 "sizeof(double)"。 程序员有责任确保
   "tp_basicsize" 是 "sizeof(double)" 的倍数（假设这是 "double" 的对齐
   要求）。

   对于任何具有可变长度实例的类型，该字段不可为 "NULL"。

   **继承：**

   这些字段将由子类分别继承。 如果基本类型有一个非零的 "tp_itemsize"，
   那么在子类型中将 "tp_itemsize" 设置为不同的非零值通常是不安全的（不
   过这取决于该基本类型的具体实现）。

destructor PyTypeObject.tp_dealloc

   指向实例析构函数的指针。除非保证类型的实例永远不会被释放（就像单例
   对象 "None" 和 "Ellipsis" 那样），否则必须定义这个函数。函数声明如
   下：

      void tp_dealloc(PyObject *self);

   当引用计数为0时，由 "Py_DECREF()" 和 "Py_XDECREF()" 宏调用析构函数
   。此时，实例仍然存在，但已经没有了对它的引用。析构函数应该释放该实
   例拥有的所有引用，释放该实例拥有的所有内存缓冲区（通过分配内存对应
   的释放函数），并调用该类型的 "tp_free" 函数。如果该类型不可子类型化
   （没有设置 "Py_TPFLAGS_BASETYPE" 标志位），则允许直接调用对象的释放
   函数，不必调用 "tp_free"。对象的释放函数应该与分配函数对应：如果使
   用 "PyObject_New()" 或 "PyObject_VarNew()" 分配，通常为
   "PyObject_Del()"；如果使用 "PyObject_GC_New()" 或
   "PyObject_GC_NewVar()" 分配，通常为 "PyObject_GC_Del()"。

   最后，如果该类型是在堆上分配的（"Py_TPFLAGS_HEAPTYPE"），释放器应该
   在调用类型释放器后减少类型对象的引用计数。为了避免空悬指针，建议的
   实现方法为：

      static void foo_dealloc(foo_object *self) {
          PyTypeObject *tp = Py_TYPE(self);
          // free references and buffers here
          tp->tp_free(self);
          Py_DECREF(tp);
      }

   **继承：**

   此字段会被子类型继承。

Py_ssize_t PyTypeObject.tp_vectorcall_offset

   An optional offset to a per-instance function that implements
   calling the object using the *vectorcall* protocol, a more
   efficient alternative of the simpler "tp_call".

   This field is only used if the flag "_Py_TPFLAGS_HAVE_VECTORCALL"
   is set. If so, this must be a positive integer containing the
   offset in the instance of a "vectorcallfunc" pointer. The signature
   is the same as for "_PyObject_Vectorcall()":

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

   The *vectorcallfunc* pointer may be zero, in which case the
   instance behaves as if "_Py_TPFLAGS_HAVE_VECTORCALL" was not set:
   calling the instance falls back to "tp_call".

   Any class that sets "_Py_TPFLAGS_HAVE_VECTORCALL" must also set
   "tp_call" and make sure its behaviour is consistent with the
   *vectorcallfunc* function. This can be done by setting *tp_call* to
   "PyVectorcall_Call":

   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 function is intended to be used in the "tp_call" slot. It
      does not fall back to "tp_call" and it currently does not check
      the "_Py_TPFLAGS_HAVE_VECTORCALL" flag. To call an object, use
      one of the "PyObject_Call" functions instead.

   注解:

     It is not recommended for heap types to implement the vectorcall
     protocol. When a user sets "__call__" in Python code, only
     "tp_call" is updated, possibly making it inconsistent with the
     vectorcall function.

   注解:

     The semantics of the "tp_vectorcall_offset" slot are provisional
     and expected to be finalized in Python 3.9. If you use
     vectorcall, plan for updating your code for Python 3.9.

   在 3.8 版更改: This slot was used for print formatting in Python
   2.x. In Python 3.0 to 3.7, it was reserved and named "tp_print".

   **继承：**

   This field is inherited by subtypes together with "tp_call": a
   subtype inherits "tp_vectorcall_offset" from its base type when the
   subtype’s "tp_call" is "NULL".

   Note that heap types (including subclasses defined in Python) do
   not inherit the "_Py_TPFLAGS_HAVE_VECTORCALL" flag.

getattrfunc PyTypeObject.tp_getattr

   一个指向获取属性字符串函数的可选指针。

   该字段已弃用。当它被定义时，应该和 "tp_getattro" 指向同一个函数，但
   接受一个C字符串参数表示属性名，而不是Python字符串对象。

   **继承：**

   分组: "tp_getattr", "tp_getattro"

   该字段会被子类和 "tp_getattro" 所继承：当子类型的 "tp_getattr" 和
   "tp_getattro" 均为 "NULL" 时该子类型将从它的基类型同时继承
   "tp_getattr" 和 "tp_getattro"。

setattrfunc PyTypeObject.tp_setattr

   一个指向函数以便设置和删除属性的可选指针。

   该字段已弃用。当它被定义时，应该和 "tp_setattro" 指向同一个函数，但
   接受一个C字符串参数表示属性名，而不是Python字符串对象。

   **继承：**

   分组: "tp_setattr", "tp_setattro"

   该字段会被子类型和 "tp_setattro" 所继承：当子类型的 "tp_setattr" 和
   "tp_setattro" 均为 "NULL" 时该子类型将同时从它的基类型继承
   "tp_setattr" 和 "tp_setattro"。

PyAsyncMethods* PyTypeObject.tp_as_async

   指向一个包含仅与在 C 层级上实现 *awaitable* 和 *asynchronous
   iterator* 协议的对象相关联的字段的附加结构体。 请参阅 异步对象结构
   体 了解详情。

   3.5 新版功能: 在之前被称为 "tp_compare" 和 "tp_reserved"。

   **继承：**

   "tp_as_async" 字段不会被继承，但所包含的字段会被单独继承。

reprfunc PyTypeObject.tp_repr

   一个实现了内置函数 "repr()" 的函数的可选指针。

   该签名与 "PyObject_Repr()" 的相同:

      PyObject *tp_repr(PyObject *self);

   该函数必须返回一个字符串或 Unicode 对象。 在理想情况下，该函数应当
   返回一个字符串，当将其传给 "eval()" 时，只要有合适的环境，就会返回
   一个具有相同值的对象。 如果这不可行，则它应当返回一个以 "'<'" 开头
   并以 "'>'" 结尾的可被用来推断出对象的类型和值的字符串。

   **继承：**

   此字段会被子类型继承。

   **默认：**

   如果未设置该字段，则返回 "<%s object at %p>" 形式的字符串，其中
   "%s" 将替换为类型名称，"%p" 将替换为对象的内存地址。

PyNumberMethods* PyTypeObject.tp_as_number

   指向一个附加结构体的指针，其中包含只与执行数字协议的对象相关的字段
   。 这些字段的文档参见 数字对象结构体。

   **继承：**

   "tp_as_number" 字段不会被继承，但所包含的字段会被单独继承。

PySequenceMethods* PyTypeObject.tp_as_sequence

   指向一个附加结构体的指针，其中包含只与执行序列协议的对象相关的字段
   。 这些字段的文档见 序列对象结构体。

   **继承：**

   "tp_as_sequence" 字段不会被继承，但所包含的字段会被单独继承。

PyMappingMethods* PyTypeObject.tp_as_mapping

   指向一个附加结构体的指针，其中包含只与执行映射协议的对象相关的字段
   。 这些字段的文档见 映射对象结构体。

   **继承：**

   "tp_as_mapping" 字段不会继承，但所包含的字段会被单独继承。

hashfunc PyTypeObject.tp_hash

   一个指向实现了内置函数 "hash()" 的函数的可选指针。

   其签名与 "PyObject_Hash()" 的相同:

      Py_hash_t tp_hash(PyObject *);

   "-1" 不应作为正常返回值被返回；当计算哈希值过程中发生错误时，函数应
   设置一个异常并返回 "-1"。

   When this field is not set (*and* "tp_richcompare" is not set), an
   attempt to take the hash of the object raises "TypeError". This is
   the same as setting it to "PyObject_HashNotImplemented()".

   此字段可被显式设为 "PyObject_HashNotImplemented()" 以阻止从父类型继
   承哈希方法。在 Python 层面这被解释为 "__hash__ = None" 的等价物，使
   得 "isinstance(o, collections.Hashable)" 正确返回 "False".。请注意
   反过来也是如此：在 Python 层面设置一个类的 "__hash__ = None" 会使得
   "tp_hash" 槽位被设置为 "PyObject_HashNotImplemented()"。

   **继承：**

   分组: "tp_hash", "tp_richcompare"

   该字段会被子类型同 "tp_richcompare" 一起继承：当子类型的
   "tp_richcompare" 和 "tp_hash" 均为 "NULL" 时子类型将同时继承
   "tp_richcompare" 和 "tp_hash"。

ternaryfunc PyTypeObject.tp_call

   一个可选的实现对象调用的指向函数的指针。 如果对象不是可调用对象则该
   值应为 "NULL"。 其签名与 "PyObject_Call()" 的相同:

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

   **继承：**

   此字段会被子类型继承。

reprfunc PyTypeObject.tp_str

   一个可选的实现内置 "str()" 操作的函数的指针。 （请注意 "str" 现在是
   一个类型，"str()" 是调用该类型的构造器。 该构造器将调用
   "PyObject_Str()" 执行实际操作，而 "PyObject_Str()" 将调用该处理器。
   ）

   其签名与 "PyObject_Str()" 的相同:

      PyObject *tp_str(PyObject *self);

   该函数必须返回一个字符串或 Unicode 对象。 它应当是一个“友好”的对象
   字符串表示形式，因为这就是要在 "print()" 函数中与其他内容一起使用的
   表示形式。

   **继承：**

   此字段会被子类型继承。

   **默认：**

   当未设置该字段时，将调用 "PyObject_Repr()" 来返回一个字符串表示形式
   。

getattrofunc PyTypeObject.tp_getattro

   一个指向获取属性字符串函数的可选指针。

   其签名与 "PyObject_GetAttr()" 的相同:

      PyObject *tp_getattro(PyObject *self, PyObject *attr);

   可以方便地将该字段设为 "PyObject_GenericGetAttr()"，它实现了查找对
   象属性的通常方式。

   **继承：**

   分组: "tp_getattr", "tp_getattro"

   该字段会被子类同 "tp_getattr" 一起继承：当子类型的 "tp_getattr" 和
   "tp_getattro" 均为 "NULL" 时子类型将同时继承 "tp_getattr" 和
   "tp_getattro"。

   **默认：**

   "PyBaseObject_Type" 使用 "PyObject_GenericGetAttr()"。

setattrofunc PyTypeObject.tp_setattro

   一个指向函数以便设置和删除属性的可选指针。

   其签名与 "PyObject_SetAttr()" 的相同:

      PyObject *tp_setattro(PyObject *self, PyObject *attr, PyObject *value);

   此外，还必须支持将 *value* 设为 "NULL" 来删除属性。 通常可以方便地
   将该字段设为 "PyObject_GenericSetAttr()"，它实现了设备对象属性的通
   常方式。

   **继承：**

   分组: "tp_setattr", "tp_setattro"

   该字段会被子类型同 "tp_setattr" 一起继承：当子类型的 "tp_setattr"
   和 "tp_setattro" 均为 "NULL" 时子类型将同时继承 "tp_setattr" 和
   "tp_setattro"。

   **默认：**

   "PyBaseObject_Type" 使用 "PyObject_GenericSetAttr()".

PyBufferProcs* PyTypeObject.tp_as_buffer

   指向一个包含只与实现缓冲区接口的对象相关的字段的附加结构体的指针。
   这些字段的文档参见 缓冲区对象结构体。

   **继承：**

   "tp_as_buffer" 字段不会被继承，但所包含的字段会被单独继承。

unsigned long PyTypeObject.tp_flags

   该字段是针对多个旗标的位掩码。 某些旗标指明用于特定场景的变化语义；
   另一些旗标则用于指明类型对象（或通过 "tp_as_number",
   "tp_as_sequence", "tp_as_mapping" 和 "tp_as_buffer" 引用的扩展结构
   体）中的特定字段，它们在历史上并不总是有效；如果这样的旗标位是清晰
   的，则它所保护的类型字段必须不可被访问并且必须被视为具有零或 "NULL"
   值。

   **继承：**

   Inheritance of this field is complicated.  Most flag bits are
   inherited individually, i.e. if the base type has a flag bit set,
   the subtype inherits this flag bit.  The flag bits that pertain to
   extension structures are strictly inherited if the extension
   structure is inherited, i.e. the base type's value of the flag bit
   is copied into the subtype together with a pointer to the extension
   structure.  The "Py_TPFLAGS_HAVE_GC" flag bit is inherited together
   with the "tp_traverse" and "tp_clear" fields, i.e. if the
   "Py_TPFLAGS_HAVE_GC" flag bit is clear in the subtype and the
   "tp_traverse" and "tp_clear" fields in the subtype exist and have
   "NULL" values.

   **默认：**

   "PyBaseObject_Type" uses "Py_TPFLAGS_DEFAULT |
   Py_TPFLAGS_BASETYPE".

   **位掩码:**

   目前定义了以下位掩码；可以使用 "|" 运算符对它们进行 OR 运算以形成
   "tp_flags" 字段的值。 宏 "PyType_HasFeature()" 接受一个类型和一个旗
   标值 *tp* 和 *f*，并检查 "tp->tp_flags & f" 是否为非零值。

   Py_TPFLAGS_HEAPTYPE

      This bit is set when the type object itself is allocated on the
      heap, for example, types created dynamically using
      "PyType_FromSpec()".  In this case, the "ob_type" field of its
      instances is considered a reference to the type, and the type
      object is INCREF'ed when a new instance is created, and
      DECREF'ed when an instance is destroyed (this does not apply to
      instances of subtypes; only the type referenced by the
      instance's ob_type gets INCREF'ed or DECREF'ed).

      **继承：**

      ？？？

   Py_TPFLAGS_BASETYPE

      当此类型可被用作另一个类型的基类型时该比特位将被设置。 如果该比
      特位被清除，则此类型将无法被子类型化（类似于 Java 中的 "final"
      类）。

      **继承：**

      ？？？

   Py_TPFLAGS_READY

      当此类型对象通过 "PyType_Ready()" 被完全实例化时该比特位将被设置
      。

      **继承：**

      ？？？

   Py_TPFLAGS_READYING

      当 "PyType_Ready()" 处在初始化此类型对象过程中时该比特位将被设置
      。

      **继承：**

      ？？？

   Py_TPFLAGS_HAVE_GC

      当此对象支持垃圾回收时该比特位将被设置。 如果设置了该比特位，则
      实例必须使用 "PyObject_GC_New()" 来创建并使用
      "PyObject_GC_Del()" 来销毁。 更多信息见 使对象类型支持循环垃圾回
      收 一节。 该比特位还表明与类型对象中存在 GC 相关字段
      "tp_traverse" 和 "tp_clear"。

      **继承：**

      分组: "Py_TPFLAGS_HAVE_GC", "tp_traverse", "tp_clear"

      The "Py_TPFLAGS_HAVE_GC" flag bit is inherited together with the
      "tp_traverse" and "tp_clear" fields, i.e.  if the
      "Py_TPFLAGS_HAVE_GC" flag bit is clear in the subtype and the
      "tp_traverse" and "tp_clear" fields in the subtype exist and
      have "NULL" values.

   Py_TPFLAGS_DEFAULT

      This is a bitmask of all the bits that pertain to the existence
      of certain fields in the type object and its extension
      structures. Currently, it includes the following bits:
      "Py_TPFLAGS_HAVE_STACKLESS_EXTENSION",
      "Py_TPFLAGS_HAVE_VERSION_TAG".

      **继承：**

      ？？？

   Py_TPFLAGS_METHOD_DESCRIPTOR

      这个位指明对象的行为类似于未绑定方法。

      如果为 "type(meth)" 设置了该旗标，那么：

      * "meth.__get__(obj, cls)(*args, **kwds)" (其中 "obj" 不为 None)
        必须等价于 "meth(obj, *args, **kwds)"。

      * "meth.__get__(None, cls)(*args, **kwds)" 必须等价于
        "meth(*args, **kwds)"。

      此旗标为 "obj.meth()" 这样的典型方法调用启用优化：它将避免为
      "obj.meth" 创建临时的“绑定方法”对象。

      3.8 新版功能.

      **继承：**

      This flag is never inherited by heap types. For extension types,
      it is inherited whenever "tp_descr_get" is inherited.

   Py_TPFLAGS_LONG_SUBCLASS

   Py_TPFLAGS_LIST_SUBCLASS

   Py_TPFLAGS_TUPLE_SUBCLASS

   Py_TPFLAGS_BYTES_SUBCLASS

   Py_TPFLAGS_UNICODE_SUBCLASS

   Py_TPFLAGS_DICT_SUBCLASS

   Py_TPFLAGS_BASE_EXC_SUBCLASS

   Py_TPFLAGS_TYPE_SUBCLASS

      这些旗标被 "PyLong_Check()" 等函数用来快速确定一个类型是否为内置
      类型的子类；这样的专用检测比泛用检测如 "PyObject_IsInstance()"
      要更快速。 继承自内置类型的自定义类型应当正确地设置其 "tp_flags"
      ，否则与这样的类型进行交互的代码将因所使用的检测种类而出现不同的
      行为。

   Py_TPFLAGS_HAVE_FINALIZE

      当类型结构体中存在 "tp_finalize" 槽位时会设置这个比特位。

      3.4 新版功能.

      3.8 版后已移除: 此旗标已不再是必要的，因为解释器会假定类型结构体
      中总是存在 "tp_finalize" 槽位。

   _Py_TPFLAGS_HAVE_VECTORCALL

      This bit is set when the class implements the vectorcall
      protocol. See "tp_vectorcall_offset" for details.

      **继承：**

      This bit is set on *static* subtypes if "tp_flags" is not
      overridden: a subtype inherits "_Py_TPFLAGS_HAVE_VECTORCALL"
      from its base type when the subtype’s "tp_call" is "NULL" and
      the subtype's "Py_TPFLAGS_HEAPTYPE" is not set.

      Heap types do not inherit "_Py_TPFLAGS_HAVE_VECTORCALL".

      注解:

        This flag is provisional and expected to become public in
        Python 3.9, with a different name and, possibly, changed
        semantics. If you use vectorcall, plan for updating your code
        for Python 3.9.

      3.8 新版功能.

const char* PyTypeObject.tp_doc

   一个可选的指向给出该类型对象的文档字符串的以 NUL 结束的 C 字符串的
   指针。 该指针被暴露为类型和类型实例上的 "__doc__" 属性。

   **继承：**

   这个字段 *不会* 被子类型继承。

traverseproc PyTypeObject.tp_traverse

   An optional pointer to a traversal function for the garbage
   collector.  This is only used if the "Py_TPFLAGS_HAVE_GC" flag bit
   is set.  The signature is:

      int tp_traverse(PyObject *self, visitproc visit, void *arg);

   有关 Python 垃圾回收方案的更多信息可在 使对象类型支持循环垃圾回收
   一节中查看。

   The "tp_traverse" pointer is used by the garbage collector to
   detect reference cycles. A typical implementation of a
   "tp_traverse" function simply calls "Py_VISIT()" on each of the
   instance's members that are Python objects that the instance owns.
   For example, this is function "local_traverse()" from the "_thread"
   extension module:

      static int
      local_traverse(localobject *self, visitproc visit, void *arg)
      {
          Py_VISIT(self->args);
          Py_VISIT(self->kw);
          Py_VISIT(self->dict);
          return 0;
      }

   请注意 "Py_VISIT()" 仅能在可以参加循环引用的成员上被调用。 虽然还存
   在一个 "self->key" 成员，但它只能为 "NULL" 或 Python 字符串因而不能
   成为循环引用的一部分。

   在另一方面，即使你知道某个成员永远不会成为循环引用的一部分，作为调
   试的辅助你仍然可能想要访问它因此 "gc" 模块的 "get_referents()" 函数
   将会包括它。

   警告:

     When implementing "tp_traverse", only the members that the
     instance *owns* (by having strong references to them) must be
     visited. For instance, if an object supports weak references via
     the "tp_weaklist" slot, the pointer supporting the linked list
     (what *tp_weaklist* points to) must **not** be visited as the
     instance does not directly own the weak references to itself (the
     weakreference list is there to support the weak reference
     machinery, but the instance has no strong reference to the
     elements inside it, as they are allowed to be removed even if the
     instance is still alive).

   请注意 "Py_VISIT()" 要求传给 "local_traverse()" 的 *visit* 和 *arg*
   形参具有指定的名称；不要随意命名它们。

   **继承：**

   分组: "Py_TPFLAGS_HAVE_GC", "tp_traverse", "tp_clear"

   This field is inherited by subtypes together with "tp_clear" and
   the "Py_TPFLAGS_HAVE_GC" flag bit: the flag bit, "tp_traverse", and
   "tp_clear" are all inherited from the base type if they are all
   zero in the subtype.

inquiry PyTypeObject.tp_clear

   An optional pointer to a clear function for the garbage collector.
   This is only used if the "Py_TPFLAGS_HAVE_GC" flag bit is set.  The
   signature is:

      int tp_clear(PyObject *);

   "tp_clear" 成员函数被用来打破垃圾回收器在循环垃圾中检测到的循环引用
   。 总的来说，系统中的所有 "tp_clear" 函数必须合到一起以打破所有引用
   循环。 这是个微妙的问题，并且如有任何疑问都需要提供 "tp_clear" 函数
   。 例如，元组类型不会实现 "tp_clear" 函数，因为有可能证明完全用元组
   是不会构成循环引用的。 因此其他类型的 "tp_clear" 函数必须足以打破任
   何包含元组的循环。 这不是立即能明确的，并且很少会有避免实现
   "tp_clear" 的适当理由。

   "tp_clear" 的实现应当丢弃实例指向其成员的可能为 Python 对象的引用，
   并将指向这些成员的指针设为 "NULL"，如下面的例子所示:

      static int
      local_clear(localobject *self)
      {
          Py_CLEAR(self->key);
          Py_CLEAR(self->args);
          Py_CLEAR(self->kw);
          Py_CLEAR(self->dict);
          return 0;
      }

   The "Py_CLEAR()" macro should be used, because clearing references
   is delicate:  the reference to the contained object must not be
   decremented until after the pointer to the contained object is set
   to "NULL".  This is because decrementing the reference count may
   cause the contained object to become trash, triggering a chain of
   reclamation activity that may include invoking arbitrary Python
   code (due to finalizers, or weakref callbacks, associated with the
   contained object). If it's possible for such code to reference
   *self* again, it's important that the pointer to the contained
   object be "NULL" at that time, so that *self* knows the contained
   object can no longer be used.  The "Py_CLEAR()" macro performs the
   operations in a safe order.

   因为 "tp_clear" 函数的目的是打破循环引用，所以不需要清除所包含的对
   象如 Python 字符串或 Python 整数，它们无法参与循环引用。 另一方面，
   清除所包含的全部 Python 对象，并编写类型的 "tp_dealloc" 函数来发起
   调用 "tp_clear" 也很方便。

   有关 Python 垃圾回收方案的更多信息可在 使对象类型支持循环垃圾回收
   一节中查看。

   **继承：**

   分组: "Py_TPFLAGS_HAVE_GC", "tp_traverse", "tp_clear"

   This field is inherited by subtypes together with "tp_traverse" and
   the "Py_TPFLAGS_HAVE_GC" flag bit: the flag bit, "tp_traverse", and
   "tp_clear" are all inherited from the base type if they are all
   zero in the subtype.

richcmpfunc PyTypeObject.tp_richcompare

   一个可选的指向富比较函数的指针，函数的签名为:

      PyObject *tp_richcompare(PyObject *self, PyObject *other, int op);

   第一个形参将保证为 "PyTypeObject" 所定义的类型的实例。

   该函数应当返回比较的结果 (通常为 "Py_True" 或 "Py_False")。 如果未
   定义比较运算，它必须返回 "Py_NotImplemented"，如果发生了其他错误则
   它必须返回 "NULL" 并设置一个异常条件。

   以下常量被定义用作 "tp_richcompare" 和 "PyObject_RichCompare()" 的
   第三个参数：

   +------------------+--------------+
   | 常量             | 对照         |
   |==================|==============|
   | "Py_LT"          | "<"          |
   +------------------+--------------+
   | "Py_LE"          | "<="         |
   +------------------+--------------+
   | "Py_EQ"          | "=="         |
   +------------------+--------------+
   | "Py_NE"          | "!="         |
   +------------------+--------------+
   | "Py_GT"          | ">"          |
   +------------------+--------------+
   | "Py_GE"          | ">="         |
   +------------------+--------------+

   定义以下宏是为了简化编写丰富的比较函数：

   Py_RETURN_RICHCOMPARE(VAL_A, VAL_B, op)

      从该函数返回 "Py_True" 或 "Py_False"，这取决于比较的结果。 VAL_A
      和 VAL_B 必须是可通过 C 比较运算符进行排序的（例如，它们可以为 C
      整数或浮点数）。 第三个参数指明所请求的运算，与
      "PyObject_RichCompare()" 的参数一样。

      The return value's reference count is properly incremented.

      发生错误时，将设置异常并从该函数返回 "NULL"。

      3.7 新版功能.

   **继承：**

   分组: "tp_hash", "tp_richcompare"

   该字段会被子类型同 "tp_hash" 一起继承：当子类型的 "tp_richcompare"
   和 "tp_hash" 均为 "NULL" 时子类型将同时继承 "tp_richcompare" 和
   "tp_hash"。

   **默认：**

   "PyBaseObject_Type" provides a "tp_richcompare" implementation,
   which may be inherited.  However, if only "tp_hash" is defined, not
   even the inherited function is used and instances of the type will
   not be able to participate in any comparisons.

Py_ssize_t PyTypeObject.tp_weaklistoffset

   If the instances of this type are weakly referenceable, this field
   is greater than zero and contains the offset in the instance
   structure of the weak reference list head (ignoring the GC header,
   if present); this offset is used by "PyObject_ClearWeakRefs()" and
   the "PyWeakref_*()" functions.  The instance structure needs to
   include a field of type "PyObject*" which is initialized to "NULL".

   不要将该字段与 "tp_weaklist" 混淆；后者是指向类型对象本身的弱引用的
   列表头。

   **继承：**

   该字段会被子类型继承，但注意参阅下面列出的规则。 子类型可以覆盖此偏
   移量；这意味着子类型将使用不同于基类型的弱引用列表。 由于列表头总是
   通过 "tp_weaklistoffset" 找到的，所以这应该不成问题。

   When a type defined by a class statement has no "__slots__"
   declaration, and none of its base types are weakly referenceable,
   the type is made weakly referenceable by adding a weak reference
   list head slot to the instance layout and setting the
   "tp_weaklistoffset" of that slot's offset.

   When a type's "__slots__" declaration contains a slot named
   "__weakref__", that slot becomes the weak reference list head for
   instances of the type, and the slot's offset is stored in the
   type's "tp_weaklistoffset".

   When a type's "__slots__" declaration does not contain a slot named
   "__weakref__", the type inherits its "tp_weaklistoffset" from its
   base type.

getiterfunc PyTypeObject.tp_iter

   An optional pointer to a function that returns an iterator for the
   object.  Its presence normally signals that the instances of this
   type are iterable (although sequences may be iterable without this
   function).

   此函数的签名与 "PyObject_GetIter()" 的相同:

      PyObject *tp_iter(PyObject *self);

   **继承：**

   此字段会被子类型继承。

iternextfunc PyTypeObject.tp_iternext

   An optional pointer to a function that returns the next item in an
   iterator. The signature is:

      PyObject *tp_iternext(PyObject *self);

   当该迭代器被耗尽时，它必须返回 "NULL"；"StopIteration" 异常可能会设
   置也可能不设置。 当发生另一个错误时，它也必须返回 "NULL"。 它的存在
   表明该类型的实际是迭代器。

   迭代器类型也应当定义 "tp_iter" 函数，并且该函数应当返回迭代器实例本
   身（而不是新的迭代器实例）。

   此函数的签名与 "PyIter_Next()" 的相同。

   **继承：**

   此字段会被子类型继承。

struct PyMethodDef* PyTypeObject.tp_methods

   一个可选的指向 "PyMethodDef" 结构体的以 "NULL" 结束的静态数组的指针
   ，它声明了此类型的常规方法。

   对于该数组中的每一项，都会向类型的字典 (参见下面的 "tp_dict") 添加
   一个包含方法描述器的条目。

   **继承：**

   该字段不会被子类型所继承（方法是通过不同的机制来继承的）。

struct PyMemberDef* PyTypeObject.tp_members

   一个可选的指向 "PyMemberDef" 结构体的以 "NULL" 结束的静态数组的指针
   ，它声明了此类型的常规数据成员（字段或槽位）。

   对于该数组中的每一项，都会向类型的字典 (参见下面的 "tp_dict") 添加
   一个包含方法描述器的条目。

   **继承：**

   该字段不会被子类型所继承（成员是通过不同的机制来继承的）。

struct PyGetSetDef* PyTypeObject.tp_getset

   一个可选的指向 "PyGetSetDef" 结构体的以 "NULL" 结束的静态数组的指针
   ，它声明了此类型的实例中的被计算属性。

   对于该数组中的每一项，都会向类型的字典 (参见下面的 "tp_dict") 添加
   一个包含读写描述器的条目。

   **继承：**

   该字段不会被子类型所继承（被计算属性是通过不同的机制来继承的）。

PyTypeObject* PyTypeObject.tp_base

   一个可选的指向类型特征属性所继承的基类型的指针。 在这个层级上，只支
   持单继承；多重继承需要通过调用元类型动态地创建类型对象。

   注解:

     槽位初始化需要遵循初始化全局变量的规则。 C99 要求初始化器为“地址
     常量”。 隐式转换为指针的函数指示器如 "PyType_GenericNew()" 都是有
     效的 C99 地址常量。However, the unary '&' operator applied to a
     non-static variable like "PyBaseObject_Type()" is not required to
     produce an address constant.  Compilers may support this (gcc
     does), MSVC does not. Both compilers are strictly standard
     conforming in this particular behavior.因此，应当在扩展模块的初始
     化函数中设置 "tp_base"。

   **继承：**

   该字段不会被子类型继承（显然）。

   **默认：**

   该字段默认为 "&PyBaseObject_Type" (对 Python 程序员来说即 "object"
   类型)。

PyObject* PyTypeObject.tp_dict

   类型的字典将由 "PyType_Ready()" 存储到这里。

   This field should normally be initialized to "NULL" before
   PyType_Ready is called; it may also be initialized to a dictionary
   containing initial attributes for the type.  Once "PyType_Ready()"
   has initialized the type, extra attributes for the type may be
   added to this dictionary only if they don't correspond to
   overloaded operations (like "__add__()").

   **继承：**

   该字段不会被子类型所继承（但在这里定义的属性是通过不同的机制来继承
   的）。

   **默认：**

   如果该字段为 "NULL"，"PyType_Ready()" 将为它分配一个新字典。

   警告:

     通过字典 C-API 使用 "PyDict_SetItem()" 或修改 "tp_dict" 是不安全
     的。

descrgetfunc PyTypeObject.tp_descr_get

   一个可选的指向“描述器获取”函数的指针。

   函数的签名为:

      PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);

   **继承：**

   此字段会被子类型继承。

descrsetfunc PyTypeObject.tp_descr_set

   一个指向用于设置和删除描述器值的函数的选项指针。

   函数的签名为:

      int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);

   将 *value* 参数设为 "NULL" 以删除该值。

   **继承：**

   此字段会被子类型继承。

Py_ssize_t PyTypeObject.tp_dictoffset

   如果该类型的实例具有一个包含实例变量的字典，则此字段将为非零值并包
   含该实例变量字典的类型的实例的偏移量；该偏移量将由
   "PyObject_GenericGetAttr()" 使用。

   不要将该字段与 "tp_dict" 混淆；后者是由类型对象本身的属性组成的字典
   。

   If the value of this field is greater than zero, it specifies the
   offset from the start of the instance structure.  If the value is
   less than zero, it specifies the offset from the *end* of the
   instance structure.  A negative offset is more expensive to use,
   and should only be used when the instance structure contains a
   variable-length part.  This is used for example to add an instance
   variable dictionary to subtypes of "str" or "tuple". Note that the
   "tp_basicsize" field should account for the dictionary added to the
   end in that case, even though the dictionary is not included in the
   basic object layout.  On a system with a pointer size of 4 bytes,
   "tp_dictoffset" should be set to "-4" to indicate that the
   dictionary is at the very end of the structure.

   The real dictionary offset in an instance can be computed from a
   negative "tp_dictoffset" as follows:

      dictoffset = tp_basicsize + abs(ob_size)*tp_itemsize + tp_dictoffset
      if dictoffset is not aligned on sizeof(void*):
          round up to sizeof(void*)

   where "tp_basicsize", "tp_itemsize" and "tp_dictoffset" are taken
   from the type object, and "ob_size" is taken from the instance.
   The absolute value is taken because ints use the sign of "ob_size"
   to store the sign of the number.  (There's never a need to do this
   calculation yourself; it is done for you by
   "_PyObject_GetDictPtr()".)

   **继承：**

   This field is inherited by subtypes, but see the rules listed
   below. A subtype may override this offset; this means that the
   subtype instances store the dictionary at a difference offset than
   the base type.  Since the dictionary is always found via
   "tp_dictoffset", this should not be a problem.

   When a type defined by a class statement has no "__slots__"
   declaration, and none of its base types has an instance variable
   dictionary, a dictionary slot is added to the instance layout and
   the "tp_dictoffset" is set to that slot's offset.

   When a type defined by a class statement has a "__slots__"
   declaration, the type inherits its "tp_dictoffset" from its base
   type.

   (Adding a slot named "__dict__" to the "__slots__" declaration does
   not have the expected effect, it just causes confusion.  Maybe this
   should be added as a feature just like "__weakref__" though.)

   **默认：**

   This slot has no default.  For static types, if the field is "NULL"
   then no "__dict__" gets created for instances.

initproc PyTypeObject.tp_init

   一个可选的指向实例初始化函数的指针。

   This function corresponds to the "__init__()" method of classes.
   Like "__init__()", it is possible to create an instance without
   calling "__init__()", and it is possible to reinitialize an
   instance by calling its "__init__()" method again.

   函数的签名为:

      int tp_init(PyObject *self, PyObject *args, PyObject *kwds);

   The self argument is the instance to be initialized; the *args* and
   *kwds* arguments represent positional and keyword arguments of the
   call to "__init__()".

   "tp_init" 函数如果不为 "NULL"，将在通过调用类型正常创建其实例时被调
   用，即在类型的 "tp_new" 函数返回一个该类型的实例时。 如果 "tp_new"
   函数返回了一个不是原始类型的子类型的其他类型的实例，则 "tp_init" 函
   数不会被调用；如果 "tp_new" 返回了一个原始类型的子类型的实例，则该
   子类型的 "tp_init" 将被调用。

   成功时返回 "0"，发生错误时则返回 "-1" 并在错误上设置一个异常。and
   sets an exception on error.

   **继承：**

   此字段会被子类型继承。

   **默认：**

   For static types this field does not have a default.

allocfunc PyTypeObject.tp_alloc

   指向一个实例分配函数的可选指针。

   函数的签名为:

      PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);

   **继承：**

   该字段会被静态子类型继承，但不会被动态子类型（通过 class 语句创建的
   子类型）继承。

   **默认：**

   对于动态子类型，该字段总是会被设为 "PyType_GenericAlloc()"，以强制
   应用标准的堆分配策略。

   For static subtypes, "PyBaseObject_Type" uses
   "PyType_GenericAlloc()".  That is the recommended value for all
   statically defined types.

newfunc PyTypeObject.tp_new

   一个可选的指向实例创建函数的指针。

   函数的签名为:

      PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds);

   The subtype argument is the type of the object being created; the
   *args* and *kwds* arguments represent positional and keyword
   arguments of the call to the type.  Note that subtype doesn't have
   to equal the type whose "tp_new" function is called; it may be a
   subtype of that type (but not an unrelated type).

   "tp_new" 函数应当调用 "subtype->tp_alloc(subtype, nitems)" 来为对象
   分配空间，然后只执行绝对有必要的进一步初始化操作。 可以安全地忽略或
   重复的初始化操作应当放在 "tp_init" 处理器中。 一个关键的规则是对于
   不可变类型来说，所有初始化操作都应当在 "tp_new" 中发生，而对于可变
   类型，大部分初始化操作都应当推迟到 "tp_init" 再执行。

   **继承：**

   This field is inherited by subtypes, except it is not inherited by
   static types whose "tp_base" is "NULL" or "&PyBaseObject_Type".

   **默认：**

   For static types this field has no default.  This means if the slot
   is defined as "NULL", the type cannot be called to create new
   instances; presumably there is some other way to create instances,
   like a factory function.

freefunc PyTypeObject.tp_free

   一个可选的指向实例释放函数的指针。 函数的签名为:

      void tp_free(void *self);

   一个兼容该签名的初始化器是 "PyObject_Free()"。

   **继承：**

   该字段会被静态子类型继承，但不会被动态子类型（通过 class 语句创建的
   子类型）继承

   **默认：**

   In dynamic subtypes, this field is set to a deallocator suitable to
   match "PyType_GenericAlloc()" and the value of the
   "Py_TPFLAGS_HAVE_GC" flag bit.

   对于静态子类型，"PyBaseObject_Type" 使用 PyObject_Del.

inquiry PyTypeObject.tp_is_gc

   可选的指向垃圾回收器所调用的函数的指针。

   The garbage collector needs to know whether a particular object is
   collectible or not.  Normally, it is sufficient to look at the
   object's type's "tp_flags" field, and check the
   "Py_TPFLAGS_HAVE_GC" flag bit.  But some types have a mixture of
   statically and dynamically allocated instances, and the statically
   allocated instances are not collectible.  Such types should define
   this function; it should return "1" for a collectible instance, and
   "0" for a non-collectible instance. The signature is:

      int tp_is_gc(PyObject *self);

   (The only example of this are types themselves.  The metatype,
   "PyType_Type", defines this function to distinguish between
   statically and dynamically allocated types.)

   **继承：**

   此字段会被子类型继承。

   **默认：**

   This slot has no default.  If this field is "NULL",
   "Py_TPFLAGS_HAVE_GC" is used as the functional equivalent.

PyObject* PyTypeObject.tp_bases

   基类型的元组。

   This is set for types created by a class statement.  It should be
   "NULL" for statically defined types.

   **继承：**

   这个字段不会被继承。

PyObject* PyTypeObject.tp_mro

   包含基类型的扩展集的元组，以类型本身开始并以 "object" 作为结束，使
   用方法解析顺序。

   **继承：**

   这个字段不会被继承；它是通过 "PyType_Ready()" 计算得到的。

PyObject* PyTypeObject.tp_cache

   尚未使用。 仅供内部使用。

   **继承：**

   这个字段不会被继承。

PyObject* PyTypeObject.tp_subclasses

   由对子类的弱引用组成的列表。 仅供内部使用。

   **继承：**

   这个字段不会被继承。

PyObject* PyTypeObject.tp_weaklist

   弱引用列表头，用于指向该类型对象的弱引用。 不会被继承。 仅限内部使
   用。

   **继承：**

   这个字段不会被继承。

destructor PyTypeObject.tp_del

   该字段已被弃用。 请改用 "tp_finalize"。

unsigned int PyTypeObject.tp_version_tag

   用于索引至方法缓存。 仅限内部使用。

   **继承：**

   这个字段不会被继承。

destructor PyTypeObject.tp_finalize

   一个可选的指向实例最终化函数的指针。 函数的签名为:

      void tp_finalize(PyObject *self);

   如果设置了 "tp_finalize"，解释器将在最终化特定实例时调用它一次。 它
   将由垃圾回收器调用（如果实例是单独循环引用的一部分）或是在对象被释
   放之前被调用。 不论是哪种方式，它都肯定会在尝试打破循环引用之前被调
   用，以确保它所操作的对象处于正常状态。

   "tp_finalize" 不应改变当前异常状态；因此，编写非关键终结器的推荐做
   法如下:

      static void
      local_finalize(PyObject *self)
      {
          PyObject *error_type, *error_value, *error_traceback;

          /* Save the current exception, if any. */
          PyErr_Fetch(&error_type, &error_value, &error_traceback);

          /* ... */

          /* Restore the saved exception. */
          PyErr_Restore(error_type, error_value, error_traceback);
      }

   For this field to be taken into account (even through inheritance),
   you must also set the "Py_TPFLAGS_HAVE_FINALIZE" flags bit.

   **继承：**

   此字段会被子类型继承。

   3.4 新版功能.

   参见: "安全的对象最终化" (**PEP 442**)

The remaining fields are only defined if the feature test macro
"COUNT_ALLOCS" is defined, and are for internal use only. They are
documented here for completeness.  None of these fields are inherited
by subtypes.

Py_ssize_t PyTypeObject.tp_allocs

   Number of allocations.

Py_ssize_t PyTypeObject.tp_frees

   Number of frees.

Py_ssize_t PyTypeObject.tp_maxalloc

   Maximum simultaneously allocated objects.

PyTypeObject* PyTypeObject.tp_prev

   Pointer to the previous type object with a non-zero "tp_allocs"
   field.

PyTypeObject* PyTypeObject.tp_next

   Pointer to the next type object with a non-zero "tp_allocs" field.

另外还需要注意，在应用垃圾回收机制的 Python 中，"tp_dealloc" 可以从任
意 Python 线程被调用，而不仅是创建该对象的线程（如果对象成为引用计数循
环的一部分，则该循环可能会被任何线程上的垃圾回收操作所回收）。 这对
Python API 调用来说不是问题，因为 tp_dealloc 调用所在的线程将持有全局
解释器锁（GIL）。 但是，如果被销毁的对象又销毁了来自其他 C 或 C++ 库的
对象，则应当小心确保在调用 tp_dealloc 的线程上销毁这些对象不会破坏这些
库的任何资源。


堆类型
======

在传统上，在 C 代码中定义的类型都是 *静态的*，也就是说，"PyTypeObject"
结构体在代码中直接定义并使用 "PyType_Ready()" 来初始化。

这就导致了与在 Python 中定义的类型相关联的类型限制：

* 静态类型只能拥有一个基类；换句话说，他们不能使用多重继承。

* 静态类型对象（但并非它们的实例）是不可变对象。 不可能在 Python 中添
  加或修改类型对象的属性。

* 静态类型对象是跨 子解释器 共享的，因此它们不应包括任何子解释器专属的
  状态。

Also, since "PyTypeObject" is not part of the stable ABI, any
extension modules using static types must be compiled for a specific
Python minor version.

An alternative to static types is *heap-allocated types*, or *heap
types* for short, which correspond closely to classes created by
Python's "class" statement.

This is done by filling a "PyType_Spec" structure and calling
"PyType_FromSpecWithBases()".


数字对象结构体
**************

PyNumberMethods

   该结构体持有指向被对象用来实现数字协议的函数的指针。 每个函数都被
   数字协议 一节中记录的对应名称的函数所使用。

   结构体定义如下:

      typedef struct {
           binaryfunc nb_add;
           binaryfunc nb_subtract;
           binaryfunc nb_multiply;
           binaryfunc nb_remainder;
           binaryfunc nb_divmod;
           ternaryfunc nb_power;
           unaryfunc nb_negative;
           unaryfunc nb_positive;
           unaryfunc nb_absolute;
           inquiry nb_bool;
           unaryfunc nb_invert;
           binaryfunc nb_lshift;
           binaryfunc nb_rshift;
           binaryfunc nb_and;
           binaryfunc nb_xor;
           binaryfunc nb_or;
           unaryfunc nb_int;
           void *nb_reserved;
           unaryfunc nb_float;

           binaryfunc nb_inplace_add;
           binaryfunc nb_inplace_subtract;
           binaryfunc nb_inplace_multiply;
           binaryfunc nb_inplace_remainder;
           ternaryfunc nb_inplace_power;
           binaryfunc nb_inplace_lshift;
           binaryfunc nb_inplace_rshift;
           binaryfunc nb_inplace_and;
           binaryfunc nb_inplace_xor;
           binaryfunc nb_inplace_or;

           binaryfunc nb_floor_divide;
           binaryfunc nb_true_divide;
           binaryfunc nb_inplace_floor_divide;
           binaryfunc nb_inplace_true_divide;

           unaryfunc nb_index;

           binaryfunc nb_matrix_multiply;
           binaryfunc nb_inplace_matrix_multiply;
      } PyNumberMethods;

   注解:

     双目和三目函数必须检查其所有操作数的类型，并实现必要的转换（至少
     有一个操作数是所定义类型的实例）。 如果没有为所给出的操作数定义操
     作，则双目和三目函数必须返回 "Py_NotImplemented"，如果发生了其他
     错误则它们必须返回 "NULL" 并设置一个异常。

   注解:

     The "nb_reserved" field should always be "NULL".  It was
     previously called "nb_long", and was renamed in Python 3.0.1.

binaryfunc PyNumberMethods.nb_add

binaryfunc PyNumberMethods.nb_subtract

binaryfunc PyNumberMethods.nb_multiply

binaryfunc PyNumberMethods.nb_remainder

binaryfunc PyNumberMethods.nb_divmod

ternaryfunc PyNumberMethods.nb_power

unaryfunc PyNumberMethods.nb_negative

unaryfunc PyNumberMethods.nb_positive

unaryfunc PyNumberMethods.nb_absolute

inquiry PyNumberMethods.nb_bool

unaryfunc PyNumberMethods.nb_invert

binaryfunc PyNumberMethods.nb_lshift

binaryfunc PyNumberMethods.nb_rshift

binaryfunc PyNumberMethods.nb_and

binaryfunc PyNumberMethods.nb_xor

binaryfunc PyNumberMethods.nb_or

unaryfunc PyNumberMethods.nb_int

void *PyNumberMethods.nb_reserved

unaryfunc PyNumberMethods.nb_float

binaryfunc PyNumberMethods.nb_inplace_add

binaryfunc PyNumberMethods.nb_inplace_subtract

binaryfunc PyNumberMethods.nb_inplace_multiply

binaryfunc PyNumberMethods.nb_inplace_remainder

ternaryfunc PyNumberMethods.nb_inplace_power

binaryfunc PyNumberMethods.nb_inplace_lshift

binaryfunc PyNumberMethods.nb_inplace_rshift

binaryfunc PyNumberMethods.nb_inplace_and

binaryfunc PyNumberMethods.nb_inplace_xor

binaryfunc PyNumberMethods.nb_inplace_or

binaryfunc PyNumberMethods.nb_floor_divide

binaryfunc PyNumberMethods.nb_true_divide

binaryfunc PyNumberMethods.nb_inplace_floor_divide

binaryfunc PyNumberMethods.nb_inplace_true_divide

unaryfunc PyNumberMethods.nb_index

binaryfunc PyNumberMethods.nb_matrix_multiply

binaryfunc PyNumberMethods.nb_inplace_matrix_multiply


映射对象结构体
**************

PyMappingMethods

   该结构体持有指向对象用于实现映射协议的函数的指针。 它有三个成员：

lenfunc PyMappingMethods.mp_length

   该函数将被 "PyMapping_Size()" 和 "PyObject_Size()" 使用，并具有相同
   的签名。 如果对象没有定义长度则此槽位可被设为 "NULL"。

binaryfunc PyMappingMethods.mp_subscript

   该函数将被 "PyObject_GetItem()" 和 "PySequence_GetSlice()" 使用，并
   具有与 "PyObject_GetItem()" 相同的签名。 此槽位必须被填充以便
   "PyMapping_Check()" 函数返回 "1"，否则它可以为 "NULL"。

objobjargproc PyMappingMethods.mp_ass_subscript

   This function is used by "PyObject_SetItem()",
   "PyObject_DelItem()", "PyObject_SetSlice()" and
   "PyObject_DelSlice()".  It has the same signature as
   "PyObject_SetItem()", but *v* can also be set to "NULL" to delete
   an item.  If this slot is "NULL", the object does not support item
   assignment and deletion.


序列对象结构体
**************

PySequenceMethods

   该结构体持有指向对象用于实现序列协议的函数的指针。

lenfunc PySequenceMethods.sq_length

   此函数被 "PySequence_Size()" 和 "PyObject_Size()" 所使用，并具有与
   它们相同的签名。 它还被用于通过 "sq_item" 和 "sq_ass_item" 槽位来处
   理负索引号。

binaryfunc PySequenceMethods.sq_concat

   此函数被 "PySequence_Concat()" 所使用并具有相同的签名。 在尝试通过
   "nb_add" 槽位执行数值相加之后它还会被用于 "+" 运算符。

ssizeargfunc PySequenceMethods.sq_repeat

   此函数被 "PySequence_Repeat()" 所使用并具有相同的签名。 在尝试通过
   "nb_multiply" 槽位执行数值相乘之后它还会被用于 "*" 运算符。

ssizeargfunc PySequenceMethods.sq_item

   此函数被 "PySequence_GetItem()" 所使用并具有相同的签名。 在尝试通过
   "mp_subscript" 槽位执行下标操作之后它还会被用于
   "PyObject_GetItem()"。 该槽位必须被填充以便 "PySequence_Check()" 函
   数返回 "1"，否则它可以为 "NULL"。

   Negative indexes are handled as follows: if the "sq_length" slot is
   filled, it is called and the sequence length is used to compute a
   positive index which is passed to "sq_item".  If "sq_length" is
   "NULL", the index is passed as is to the function.

ssizeobjargproc PySequenceMethods.sq_ass_item

   此函数被 "PySequence_SetItem()" 所使用并具有相同的签名。 在尝试通过
   "mp_ass_subscript" 槽位执行条目赋值和删除操作之后它还会被用于
   "PyObject_SetItem()" 和 "PyObject_DelItem()"。 如果对象不支持条目和
   删除则该槽位可以保持为 "NULL"。

objobjproc PySequenceMethods.sq_contains

   该函数可供 "PySequence_Contains()" 使用并具有相同的签名。 此槽位可
   以保持为 "NULL"，在此情况下 "PySequence_Contains()" 只需遍历该序列
   直到找到一个匹配。

binaryfunc PySequenceMethods.sq_inplace_concat

   此函数被 "PySequence_InPlaceConcat()" 所使用并具有相同的签名。 它应
   当修改它的第一个操作数，并将其返回。 该槽位可以保持为 "NULL"，在此
   情况下 "PySequence_InPlaceConcat()" 将回退到 "PySequence_Concat()"
   。 在尝试通过 "nb_inplace_add" 槽位执行数字原地相加之后它还会被用于
   增强赋值运算符 "+="。

ssizeargfunc PySequenceMethods.sq_inplace_repeat

   此函数被 "PySequence_InPlaceRepeat()" 所使用并具有相同的签名。 它应
   当修改它的第一个操作数，并将其返回。 该槽位可以保持为 "NULL"，在此
   情况下 "PySequence_InPlaceRepeat()" 将回退到 "PySequence_Repeat()"
   。 在尝试通过 "nb_inplace_multiply" 槽位执行数字原地相乘之后它还会
   被用于增强赋值运算符 "*="。


缓冲区对象结构体
****************

PyBufferProcs

   此结构体持有指向 缓冲区协议 所需要的函数的指针。 该协议定义了导出方
   对象要如何向消费方对象暴露其内部数据。

getbufferproc PyBufferProcs.bf_getbuffer

   此函数的签名为:

      int (PyObject *exporter, Py_buffer *view, int flags);

   处理发给 *exporter* 的请求来填充 *flags* 所指定的 *view*。 除第 (3)
   点外，此函数的实现必须执行以下步骤：

   1. Check if the request can be met. If not, raise
      "PyExc_BufferError", set "view->obj" to "NULL" and return "-1".

   2. 填充请求的字段。

   3. 递增用于保存导出次数的内部计数器。

   4. Set "view->obj" to *exporter* and increment "view->obj".

   5. 返回 "0"。

   如果 *exporter* 是缓冲区提供方的链式或树型结构的一部分，则可以使用
   两种主要方案：

   * Re-export: Each member of the tree acts as the exporting object
     and sets "view->obj" to a new reference to itself.

   * Redirect: The buffer request is redirected to the root object of
     the tree. Here, "view->obj" will be a new reference to the root
     object.

   *view* 中每个字段的描述参见 缓冲区结构体 一节，导出方对于特定请求应
   当如何反应参见 缓冲区请求类型 一节。

   所有在 "Py_buffer" 结构体中被指向的内存都属于导出方并必须保持有效直
   到不再有任何消费方。 "format", "shape", "strides", "suboffsets" 和
   "internal" 对于消费方来说是只读的。

   "PyBuffer_FillInfo()" 提供了一种暴露简单字节缓冲区同时正确处理地所
   有请求类型的简便方式。

   "PyObject_GetBuffer()" 是针对包装此函数的消费方的接口。

releasebufferproc PyBufferProcs.bf_releasebuffer

   此函数的签名为:

      void (PyObject *exporter, Py_buffer *view);

   处理释放缓冲区资源的请求。 如果不需要释放任何资源，则
   "PyBufferProcs.bf_releasebuffer" 可以为 "NULL"。 在其他情况下，此函
   数的标准实现将执行以下的可选步骤：

   1. 递减用于保存导出次数的内部计数器。

   2. 如果计数器为 "0"，则释放所有关联到 *view* 的内存。

   导出方必须使用 "internal" 字段来记录缓冲区专属的资源。 该字段将确保
   恒定，而消费方则可能将原始缓冲区作为 *view* 参数传入。

   This function MUST NOT decrement "view->obj", since that is done
   automatically in "PyBuffer_Release()" (this scheme is useful for
   breaking reference cycles).

   "PyBuffer_Release()" 是针对包装此函数的消费方的接口。


异步对象结构体
**************

3.5 新版功能.

PyAsyncMethods

   此结构体将持有指向需要用来实现 *awaitable* 和 *asynchronous
   iterator* 对象的函数的指针。

   结构体定义如下:

      typedef struct {
          unaryfunc am_await;
          unaryfunc am_aiter;
          unaryfunc am_anext;
      } PyAsyncMethods;

unaryfunc PyAsyncMethods.am_await

   此函数的签名为:

      PyObject *am_await(PyObject *self);

   The returned object must be an iterator, i.e. "PyIter_Check()" must
   return "1" for it.

   如果一个对象不是 *awaitable* 则此槽位可被设为 "NULL"。

unaryfunc PyAsyncMethods.am_aiter

   此函数的签名为:

      PyObject *am_aiter(PyObject *self);

   Must return an *awaitable* object.  See "__anext__()" for details.

   如果一个对象没有实现异步迭代协议则此槽位可被设为 "NULL"。

unaryfunc PyAsyncMethods.am_anext

   此函数的签名为:

      PyObject *am_anext(PyObject *self);

   Must return an *awaitable* object.  See "__anext__()" for details.
   This slot may be set to "NULL".


槽位类型 typedef
****************

PyObject *(*allocfunc)(PyTypeObject *cls, Py_ssize_t nitems)

   The purpose of this function is to separate memory allocation from
   memory initialization.  It should return a pointer to a block of
   memory of adequate length for the instance, suitably aligned, and
   initialized to zeros, but with "ob_refcnt" set to "1" and "ob_type"
   set to the type argument.  If the type's "tp_itemsize" is non-zero,
   the object's "ob_size" field should be initialized to *nitems* and
   the length of the allocated memory block should be "tp_basicsize +
   nitems*tp_itemsize", rounded up to a multiple of "sizeof(void*)";
   otherwise, *nitems* is not used and the length of the block should
   be "tp_basicsize".

   此函数不应执行任何其他实例初始化操作，即使是分配额外内存也不应执行
   ；那应当由 "tp_new" 来完成。

void (*destructor)(PyObject *)

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

   See "tp_vectorcall_offset".

   Arguments to "vectorcallfunc" are the same as for
   "_PyObject_Vectorcall()".

   3.8 新版功能.

void (*freefunc)(void *)

   参见 "tp_free"。

PyObject *(*newfunc)(PyObject *, PyObject *, PyObject *)

   参见 "tp_new"。

int (*initproc)(PyObject *, PyObject *, PyObject *)

   参见 "tp_init"。

PyObject *(*reprfunc)(PyObject *)

   参见 "tp_repr"。

PyObject *(*getattrfunc)(PyObject *self, char *attr)

   返回对象的指定属性的值。

int (*setattrfunc)(PyObject *self, char *attr, PyObject *value)

   为对象设置指定属性的值。 将 value 参数设为 "NULL" 将删除该属性。

PyObject *(*getattrofunc)(PyObject *self, PyObject *attr)

   返回对象的指定属性的值。

   参见 "tp_getattro"。

int (*setattrofunc)(PyObject *self, PyObject *attr, PyObject *value)

   为对象设置指定属性的值。 将 value 参数设为 "NULL" 将删除该属性。

   参见 "tp_setattro"。

PyObject *(*descrgetfunc)(PyObject *, PyObject *, PyObject *)

   See "tp_descrget".

int (*descrsetfunc)(PyObject *, PyObject *, PyObject *)

   See "tp_descrset".

Py_hash_t (*hashfunc)(PyObject *)

   参见 "tp_hash"。

PyObject *(*richcmpfunc)(PyObject *, PyObject *, int)

   参见 "tp_richcompare"。

PyObject *(*getiterfunc)(PyObject *)

   参见 "tp_iter"。

PyObject *(*iternextfunc)(PyObject *)

   参见 "tp_iternext"。

Py_ssize_t (*lenfunc)(PyObject *)

int (*getbufferproc)(PyObject *, Py_buffer *, int)

void (*releasebufferproc)(PyObject *, Py_buffer *)

PyObject *(*unaryfunc)(PyObject *)

PyObject *(*binaryfunc)(PyObject *, PyObject *)

PyObject *(*ternaryfunc)(PyObject *, PyObject *, PyObject *)

PyObject *(*ssizeargfunc)(PyObject *, Py_ssize_t)

int (*ssizeobjargproc)(PyObject *, Py_ssize_t)

int (*objobjproc)(PyObject *, PyObject *)

int (*objobjargproc)(PyObject *, PyObject *, PyObject *)


例子
****

下面是一些 Python 类型定义的简单示例。 其中包括你可能会遇到的通常用法
。 有些演示了令人困惑的边际情况。 要获取更多示例、实践信息以及教程，请
参阅 自定义扩展类型：教程 和 定义扩展类型：已分类主题。

A basic static type:

   typedef struct {
       PyObject_HEAD
       const char *data;
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject),
       .tp_doc = "My objects",
       .tp_new = myobj_new,
       .tp_dealloc = (destructor)myobj_dealloc,
       .tp_repr = (reprfunc)myobj_repr,
   };

你可能还会看到带有更繁琐的初始化器的较旧代码（特别是在 CPython 代码库
中）:

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       "mymod.MyObject",               /* tp_name */
       sizeof(MyObject),               /* tp_basicsize */
       0,                              /* tp_itemsize */
       (destructor)myobj_dealloc,      /* tp_dealloc */
       0,                              /* tp_vectorcall_offset */
       0,                              /* tp_getattr */
       0,                              /* tp_setattr */
       0,                              /* tp_as_async */
       (reprfunc)myobj_repr,           /* tp_repr */
       0,                              /* tp_as_number */
       0,                              /* tp_as_sequence */
       0,                              /* tp_as_mapping */
       0,                              /* tp_hash */
       0,                              /* tp_call */
       0,                              /* tp_str */
       0,                              /* tp_getattro */
       0,                              /* tp_setattro */
       0,                              /* tp_as_buffer */
       0,                              /* tp_flags */
       "My objects",                   /* tp_doc */
       0,                              /* tp_traverse */
       0,                              /* tp_clear */
       0,                              /* tp_richcompare */
       0,                              /* tp_weaklistoffset */
       0,                              /* tp_iter */
       0,                              /* tp_iternext */
       0,                              /* tp_methods */
       0,                              /* tp_members */
       0,                              /* tp_getset */
       0,                              /* tp_base */
       0,                              /* tp_dict */
       0,                              /* tp_descr_get */
       0,                              /* tp_descr_set */
       0,                              /* tp_dictoffset */
       0,                              /* tp_init */
       0,                              /* tp_alloc */
       myobj_new,                      /* tp_new */
   };

一个支持弱引用、实例字典和哈希运算的类型:

   typedef struct {
       PyObject_HEAD
       const char *data;
       PyObject *inst_dict;
       PyObject *weakreflist;
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject),
       .tp_doc = "My objects",
       .tp_weaklistoffset = offsetof(MyObject, weakreflist),
       .tp_dictoffset = offsetof(MyObject, inst_dict),
       .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
       .tp_new = myobj_new,
       .tp_traverse = (traverseproc)myobj_traverse,
       .tp_clear = (inquiry)myobj_clear,
       .tp_alloc = PyType_GenericNew,
       .tp_dealloc = (destructor)myobj_dealloc,
       .tp_repr = (reprfunc)myobj_repr,
       .tp_hash = (hashfunc)myobj_hash,
       .tp_richcompare = PyBaseObject_Type.tp_richcompare,
   };

A str subclass that cannot be subclassed and cannot be called to
create instances (e.g. uses a separate factory func):

   typedef struct {
       PyUnicodeObject raw;
       char *extra;
   } MyStr;

   static PyTypeObject MyStr_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyStr",
       .tp_basicsize = sizeof(MyStr),
       .tp_base = NULL,  // set to &PyUnicode_Type in module init
       .tp_doc = "my custom str",
       .tp_flags = Py_TPFLAGS_DEFAULT,
       .tp_new = NULL,
       .tp_repr = (reprfunc)myobj_repr,
   };

The simplest static type (with fixed-length instances):

   typedef struct {
       PyObject_HEAD
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
   };

The simplest static type (with variable-length instances):

   typedef struct {
       PyObject_VAR_HEAD
       const char *data[1];
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject) - sizeof(char *),
       .tp_itemsize = sizeof(char *),
   };
