4.12 Python列表和元组的底层实现

有关列表（list）和元组（tuple）的底层实现，本节分别从它们的源码来进行分析。

首先来分析 list 列表，它的具体结构如下所示：

/* List object interface */
/*
Another generally useful object type is a list of object pointers.
This is a mutable type: the list items can be changed, and items can be
added or removed.  Out-of-range indices or non-list objects are ignored.
*** WARNING *** PyList_SetItem does not increment the new item's reference
count, but does decrement the reference count of the item it replaces,
if not nil.  It does *decrement* the reference count if it is *not*
inserted in the list.  Similarly, PyList_GetItem does not increment the
returned item's reference count.
*/
#ifndef Py_LISTOBJECT_H
#define Py_LISTOBJECT_H
#ifdef __cplusplus
extern "C" {
   
#endif
#ifndef Py_LIMITED_API
typedef struct {
   
    PyObject_VAR_HEAD
/* Vector of pointers to list elements.  list[0] is ob_item[0], etc. */
    PyObject **ob_item;
/* ob_item contains space for 'allocated' elements.  The number
     * currently in use is ob_size.
     * Invariants:
     *     0 <= ob_size <= allocated
     *     len(list) == ob_size
     *     ob_item == NULL implies ob_size == allocated == 0
     * list.sort() temporarily sets allocated to -1 to detect mutations.
     *
     * Items must normally not be NULL, except during construction when
     * the list is not yet visible outside the function that builds it.
     */
    Py_ssize_t allocated;
} PyListObject;
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