Something haunts me in Python

@1:　　在查看"The Python Library Reference"(https://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange)

的时候发现了这样的一段代码：

代码1：

>>> lists = [[]] * 3
>>> lists
[[], [], []]
>>> lists[0].append(3)
>>> lists

　　执行完lists[0].append(3)之后，程序将输出什么结果？ [[3], [0], [0]]？

　　正确答案是[[3], [3], [3]]，让我们来看看Reference上的解释：

　　This often haunts new Python programmers. What has happened is that [[]] is a one-element list containing an empty

list, so all three elements of [[]] * 3 are (pointers to) this single empty list. Modifying any of the elements of lists modifies

this single list. You can create a list of different lists this way:

代码2：

>>> lists = [[] for i in range(3)]
>>> lists[0].append(3)　　# 此时lists为[[3], [], []]
>>> lists[1].append(5)
>>> lists[2].append(7)
>>> lists
[[3], [5], [7]]

　　补充：代码1中lists的三个元素都指向同一个空list，是因为：s * n, n * s --- n shallow copies of s concatenated，

即Python中的*运算采用的是浅复制。

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Something haunts me in Python

原文：http://www.cnblogs.com/lxw0109/p/note_in_python.html