0.3.4　定長(zhǎng)對(duì)象和變長(zhǎng)對(duì)象

除了0.3.2節(jié)提到的分類方法外，還可以根據(jù)是否包含可變長(zhǎng)度數(shù)據(jù)將Python對(duì)象分為定長(zhǎng)對(duì)象和變長(zhǎng)對(duì)象這兩種形式。定長(zhǎng)對(duì)象指不包含可變長(zhǎng)度數(shù)據(jù)的對(duì)象，如整數(shù)對(duì)象；變長(zhǎng)對(duì)象指包含可變長(zhǎng)度數(shù)據(jù)的對(duì)象，如字符串對(duì)象。

變長(zhǎng)對(duì)象都擁有一個(gè)相同的PyVarObject對(duì)象，而PyVarObject是基于PyObject擴(kuò)展的。

PyVarObject的相關(guān)源碼（Include/object.h）如下：

// Include/object.h
typedef struct _object {
    _PyObject_HEAD_EXTRA
    Py_ssize_t ob_refcnt;
    struct _typeobject *ob_type;
} PyObject;

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

從代碼中可以看出，PyVarObject比PyObject多出了一個(gè)用于存儲(chǔ)元素個(gè)數(shù)的變量ob_size。PyVarObject的簡(jiǎn)單圖形表示如圖0-4所示。

圖0-4　PyVarObject的簡(jiǎn)單圖形表示