[docs] Little Tutorial Correction

Georg Brandl georg at python.org
Thu Sep 22 10:29:37 CEST 2011


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Am 22.09.2011 10:12, schrieb Petersen, Eike:
> Hello,
> 
> http://docs.python.org/tutorial/introduction.html#lists under this section
> I read across the following statement:
> 
> ?All slice operations return a new list containing the requested elements. 
> This means that the following slice returns a shallow copy of the list 
> //a//:
> 
>>>> a[:]?
> 
> But as far as I know the behaviour of the [:] operator is on the contrary 
> called deep copying, since the following will return different lists:
> 
> A = [1,2,3] B =A[:] A[1]=3

Hi Eike,

Python does indeed to only a shallow copy, since it does not copy the objects
themselves.  To see this, you can try something like this:

>>> a = [[1, 2], [3]] b = a[:] a[0][0] = 999 a[0]
[999, 2]
>>> b[0]
[999, 2]

cheers,
Georg
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