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List:       python-list
Subject:    Re: Help! I need a list, not a pointer to it
From:       Gabriel Genellina <gagsl-py () yahoo ! com ! ar>
Date:       2006-11-21 23:49:18
Message-ID: 7.0.1.0.0.20061121204215.040f31e0 () yahoo ! com ! ar
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At Tuesday 21/11/2006 19:53, Sorin Schwimmer wrote:

>solutions=[]
>matrix=[[1.0], [0], [0]]
>j=0
>while j<c:
>   [...modify matrix...]
>   print matrix
>   solutions.append(matrix) # same result with matrix[:]
>print solutions
>
>gives:
>[[0], [1.0], [0]]
>[[0], [0], [1.0]]
>[[1.0], [0], [0]]
>[[[1.0], [0], [0]], [[1.0], [0], [0]], [[1.0], [0], [0]]]
>(i.e. the last value of matrix, three times)
>
>How can I end up with:
>[[0], [1.0], [0]]
>[[0], [0], [1.0]]
>[[1.0], [0], [0]]
>[[[0], [1.0], [0]], [[0], [0], [1.0]], [[1.0], [0], [0]]]
>(i.e. each value of matrix)?

Using matrix[:] gives you a _shallow_ copy of matrix - a new list, 
but its elements (lists themselves) are the original ones.
You may want to use deepcopy() instead (or redesign your algorithm to 
not use those inner lists).


-- 
Gabriel Genellina
Softlab SRL 

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