Python列表的長度調(diào)節(jié)方法（附代碼）

>>> test = []
>>> test.append(1)
>>> test.append({2})
>>> test.append([3])
>>> print test

# 

test = []

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

# 

import sys

test = []
test_1 = [1]
print sys.getsizeof(test)
print sys.getsizeof(test_1) - sys.getsizeof(test)

# 

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對象指針的緩存
 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 成員的內(nèi)存申請
 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 int
list_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, ...
 */
 # 確定新擴(kuò)展之后的占坑數(shù)
 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;

 # 申請內(nèi)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: utf8
import sys

test = []
raw_size = sys.getsizeof(test)

test.append(1)
print "1 次 append 減去空列表的內(nèi)存大小：%s " % (sys.getsizeof(test) - raw_size)

test.append(1)
print "2 次 append 減去空列表的內(nèi)存大?。?s " % (sys.getsizeof(test) - raw_size)

test.append(1)
print "3 次 append 減去空列表的內(nèi)存大小：%s " % (sys.getsizeof(test) - raw_size)

test.append(1)
print "4 次 append 減去空列表的內(nèi)存大?。?s " % (sys.getsizeof(test) - raw_size)

test.append(1)
print "5 次 append 減去空列表的內(nèi)存大小：%s " % (sys.getsizeof(test) - raw_size)

test.append(1)
print "6 次 append 減去空列表的內(nèi)存大?。?s " % (sys.getsizeof(test) - raw_size)

# 

test = []

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