[Python-Dev] docs - Copy

Fri Jun 25 03:04:03 CEST 2010

Rich Healey wrote:
> http://docs.python.org/library/copy.html
>> Just near the bottom it reads:
>> """Shallow copies of dictionaries can be made using dict.copy(), and
> of lists by assigning a slice of the entire list, for example,
> copied_list = original_list[:]."""
>>> Surely this is a typo? To my understanding, copied_list =
> original_list[:] gives you a clean copy (slicing returns a new
> object....)
>Yes, but it's a shallow copy: the new object references exactly the same
objects as the original list (not copies of those objects). A deep copy
would need to copy any referenced lists, and so on.
> Can this be updated? Or someone explain to me why it's correct?
>It sounds correct to me.
regards
 Steve
> Cheers
>> Example:
>>>>>> t = [1, 2, 3]
>>>> y = t
>>>> u = t[:]
>>>> y[1] = "rawr"
>>>> t
> [1, 'rawr', 3]
>>>> u
> [1, 2, 3]

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