Python列表的长度调节方法（附代码）

>>> test = []>>> test.append(1)>>> test.append({2})>>> test.append([3])>>> print test# 输出 [1, set([2]), [3]]

test = []for i in range(4):    test.append(i)print test# 输出 [0, 1, 2, 3]

import systest = []test_1 = [1]print sys.getsizeof(test)print sys.getsizeof(test_1) - sys.getsizeof(test)# 输出 72     # 空列表内存大小，也是 list 对象的总大小8       # 代表增加一个成员，list 增加的大小

PyObject *PyList_New(Py_ssize_t size){    PyListObject *op;    size_t nbytes;    if (size < 0) {        PyErr_BadInternalCall();        return NULL;    }    /* Check for overflow without an actual overflow,     *  which can cause compiler to optimise out */    if ((size_t)size > PY_SIZE_MAX / sizeof(PyObject *))        return PyErr_NoMemory();            // list对象指针的缓存    if (numfree) {        numfree--;        op = free_list[numfree];        _Py_NewReference((PyObject *)op);    } else {        op = PyObject_GC_New(PyListObject, &PyList_Type);        if (op == NULL)            return NULL;    }        // list 成员的内存申请    nbytes = size * sizeof(PyObject *);    if (size <= 0)        op->ob_item = NULL;    else {        op->ob_item = (PyObject **) PyMem_MALLOC(nbytes);        if (op->ob_item == NULL) {            Py_DECREF(op);            return PyErr_NoMemory();        }        memset(op->ob_item, 0, nbytes);    }    Py_SIZE(op) = size;    op->allocated = size;    _PyObject_GC_TRACK(op);    return (PyObject *) op;}

#define PyList_SET_ITEM(op, i, v) (((PyListObject *)(op))->ob_item[i] = (v))

static intlist_resize(PyListObject *self, Py_ssize_t newsize){    PyObject **items;    size_t new_allocated;    Py_ssize_t allocated = self->allocated;    /* Bypass realloc() when a previous overallocation is large enough       to accommodate the newsize.  If the newsize falls lower than half       the allocated size, then proceed with the realloc() to shrink the list.    */    if (allocated >= newsize && newsize >= (allocated >> 1)) {        assert(self->ob_item != NULL || newsize == 0);        Py_SIZE(self) = newsize;        return 0;    }    /* This over-allocates proportional to the list size, making room     * for additional growth.  The over-allocation is mild, but is     * enough to give linear-time amortized behavior over a long     * sequence of appends() in the presence of a poorly-performing     * system realloc().     * The growth pattern is:  0, 4, 8, 16, 25, 35, 46, 58, 72, 88, ...     */    # 确定新扩展之后的占坑数    new_allocated = (newsize >> 3) + (newsize < 9 ? 3 : 6);    /* check for integer overflow */    if (new_allocated > PY_SIZE_MAX - newsize) {        PyErr_NoMemory();        return -1;    } else {        new_allocated += newsize;    }    if (newsize == 0)        new_allocated = 0;    # 申请内存    items = self->ob_item;    if (new_allocated <= (PY_SIZE_MAX / sizeof(PyObject *)))        PyMem_RESIZE(items, PyObject *, new_allocated);    else        items = NULL;    if (items == NULL) {        PyErr_NoMemory();        return -1;    }    self->ob_item = items;    Py_SIZE(self) = newsize;    self->allocated = new_allocated;    return 0;}

a = [1, 2, 3]a.append(1)

 0 <= ob_size <= allocated len(list) == ob_size

#coding: utf8import systest = []raw_size = sys.getsizeof(test)test.append(1)print "1 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)test.append(1)print "2 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)test.append(1)print "3 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)test.append(1)print "4 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)test.append(1)print "5 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)test.append(1)print "6 次 append 减去空列表的内存大小：%s " % (sys.getsizeof(test) - raw_size)

# 输出结果1 次 append 减去空列表的内存大小：322 次 append 减去空列表的内存大小：323 次 append 减去空列表的内存大小：324 次 append 减去空列表的内存大小：325 次 append 减去空列表的内存大小：646 次 append 减去空列表的内存大小：64

test = []for i in range(4):    test.append(i)print test