copying a list

[Kalle Svensson]

On Tue, 8 Aug 2000, lance wrote:

> is there an easy way to get a copy of a list instead of a reference to that
> list?

The easiest way is by using the slice:

>>> x = [1, 2]
>>> y = x[:]
>>> y[1] = 3
>>> x, y
([1, 2], [1, 3])

If you use nested lists this might not be good enough:

>>> x = [[1, 2], [3, 4]]
>>> y = x[:]
>>> y[1][1] = 5
>>> x, y
([[1, 2], [3, 5]], [[1, 2], [3, 5]])
              ^
In this case, use deepcopy from the copy module (in the standard library):

>>> x = [[1, 2], [3, 4]]
>>> import copy
>>> y = copy.deepcopy(x)
>>> y[1][1] = 5
>>> x, y
([[1, 2], [3, 4]], [[1, 2], [3, 5]])

HTH,
  Kalle Svensson

-- 
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