一：PyObject

  首先，先來看PyObject在object.h中的定義。

typedef struct _object {
    _PyObject_HEAD_EXTRA
    Py_ssize_t ob_refcnt;
    struct _typeobject *ob_type;
} PyObject;

#ifdef Py_TRACE_REFS
/* Define pointers to support a doubly-linked list of all live heap objects. */
#define _PyObject_HEAD_EXTRA            \
    struct _object *_ob_next;           \
    struct _object *_ob_prev;

#define _PyObject_EXTRA_INIT 0, 0,

#else
#define _PyObject_HEAD_EXTRA
#define _PyObject_EXTRA_INIT
#endif
 

typedef struct _typeobject PyTypeObject;

  Py_ssize_t ob_refcnt、 struct _typeobject *ob_type。

 1、_PyObject_HEAD_EXTRA是一個巨集，它的定義與Py_TRACE_REFS有關，即當編譯時會執行else語句，導致_PyObject_HEAD_EXTRA定義為空；

  2、Py_ssize_t ob_refcnt在編譯時確定為一個整型，是一個引用計數（與python的記憶體管理機制有關）；

  3、struct _typeobject *ob_type是一個指向_tyepobject的指標，是一個型別物件。

二：PyTypeObject

 我們再來看看PyTypeObject在object.h中的定義。

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;
    printfunc tp_print;
    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 */

    /* Assigned meaning in release 2.0 */
    /* call function for all accessible objects */
    traverseproc tp_traverse;

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

    /* Assigned meaning in release 2.1 */
    /* 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;

#ifdef COUNT_ALLOCS
    /* these must be last and never explicitly initialized */
    Py_ssize_t tp_allocs;
    Py_ssize_t tp_frees;
    Py_ssize_t tp_maxalloc;
    struct _typeobject *tp_prev;
    struct _typeobject *tp_next;
#endif
} PyTypeObject;
#endif
 

#define PyObject_VAR_HEAD      PyVarObject ob_base;

  PyTypeObject物件是一個結構體，是一個型別物件。可以看見其中包含很多東西：PyObject_VAR_HEAD、const char *tp_name、Py_ssize_t tp_basicsize, tp_itemsize、還有各種方法、函式、屬性、指標等（關於這部分會慢慢解釋）。

  1、PyObject_VAR_HEAD：是一個巨集，可以看見該巨集定義中包含了包含了PyVarObject物件的定義。

  2、const char *tp_name：指向一個固定char型記憶體的指標，表示型別名（在python內部進行除錯的時候用）

  3、Py_ssize_t tp_basicsize, tp_itemsize：建立該型別物件時分配記憶體空間的大小的資訊（兩個整型資料）

三：PyVarObject

#define PyObject_VAR_HEAD      PyVarObject ob_base;

typedef struct {
    PyObject ob_base;
    Py_ssize_t ob_size; /* Number of items in variable part */
} PyVarObject;

  PyVarObject是一個結構體，表示變長物件（如list、字典、String等物件）。其中包含兩個部分：PyObject ob_base、Py_ssize_t ob_size。

  1、PyObject ob_base：是一個PyObject型的物件。

  2、Py_ssize_t ob_size：是一個整型資料，用來表示變長物件的元素的個數。

四：三者的關係圖