源码

Include/object.h

/* Nothing is actually declared to be a PyObject, but every pointer to
 * a Python object can be cast to a PyObject*.  This is inheritance built
 * by hand.  Similarly every pointer to a variable-size Python object can,
 * in addition, be cast to PyVarObject*.
 */
typedef struct _object {
    _PyObject_HEAD_EXTRA   // 如果开启了 Py_TRACE_REFS 增加一个 _ob_next, _ob_prev
                           // 使 all live heap objects 组成一个双向链表
    Py_ssize_t ob_refcnt;  // 长整型
    PyTypeObject *ob_type;
} PyObject;

/* Cast argument to PyObject* type. */
#define _PyObject_CAST(op) ((PyObject*)(op))
#define _PyObject_CAST_CONST(op) ((const PyObject*)(op))

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

/* Cast argument to PyVarObject* type. */
#define _PyVarObject_CAST(op) ((PyVarObject*)(op))

#define Py_REFCNT(ob)           (_PyObject_CAST(ob)->ob_refcnt)
#define Py_TYPE(ob)             (_PyObject_CAST(ob)->ob_type)
#define Py_SIZE(ob)             (_PyVarObject_CAST(ob)->ob_size)

PyObject

相当于所有 Python 对象的父类，包含类型，引用计数等信息。

注释说的很清楚，不会有直接声明的 PyObject 变量，只会有 PyObject* 指针，所有指向 Python 对象的指针都可以转换成 PyObject*。

PyVarObject

表示 ob_size 个 PyObject，也就是说 PyVarObject 是一个 PyObject 的容器。