Copying nested lists in Python

python list copy deep-copy
SuperString picture SuperString · Mar 30, 2010 · Viewed 32.3k times · Source

I want to copy a 2D list, so that if I modify one list, the other is not modified.

For a one-dimensional list, I just do this:

a = [1, 2]
b = a[:]

And now if I modify b, a is not modified.

But this doesn't work for a two-dimensional list:

a = [[1, 2],[3, 4]]
b = a[:]

If I modify b, a gets modified as well.

How do I fix this?

Answer

Ayman Hourieh picture Ayman Hourieh · Mar 30, 2010

For a more general solution that works regardless of the number of dimensions, use copy.deepcopy():

import copy
b = copy.deepcopy(a)

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