List repetition and memory

Question

Consider this code:

lst = [['a']*5]*4
lst[1][1] = '*'

And this code:

lst= [['a'] * 5 for i in range(4)]
lst[1][1] = '*'

What makes them different?

Thanks

Also possible duplicate of [Python List Problem](http://stackoverflow.com/questions/1959744/python-list-problem) — Mp0int, Dec 07 '13 at 14:11

score 2 · Answer 1 · answered Dec 07 '13 at 14:05

2

Those are the same objects:

>>> lst = [['a']*2]*2
>>> map(id, lst)
[60543624, 60543624]
>>> lst[0] is lst[1]
True

answered Dec 07 '13 at 14:05

alko

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thefourtheye · Accepted Answer · 2013-12-07T14:10:57.033

1

Because, you are not creating four lists with 5 as in them. Instead, you are creating 4 lists which point to the same list with 5 as in it. So, you change one, the effect is seen in all others as well.

edited Dec 07 '13 at 14:10

answered Dec 07 '13 at 14:05

thefourtheye

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List repetition and memory

2 Answers2