Why is this?

[Jan-Ole Esleben]

For the sake of completeness (I didn't copy this message to the list):

> I have a problem with initialization.
> >>> a, b = [[]]*2
> >>> a.append(1)
> >>> b
> [1]
>
> Why is this? Why does not this behave like the below:

You create a single list (inside your brachets) and duplicate a
reference to it. a and b are two references to the same list; this is
just a problem for mutable objects, but I think it's safe to say that
it bites everyone at some point.

> >>> [[], []] == [[]]*2
> True

Obviously, this is not a test for referential identity.

Hope this helps to clear the matter up!
Ole


2005/8/10, Jiri Barton <jbar at hosting4u.cz>:
> Yes, now it is clear!
> 
> As always, I should have RTFM, the operator* is not just a syntactic sugar
> and thus does not make copies. You know, my actual scenario was with four
> variables at the time:
> 
> a, b, c, d = [], [], [], []
> 
> so I was even more tempted to use the previous and wrong approach:-)
> 
> Thank you for your explanation. No more errors in my code from now on (oh
> well,...)
> 
> jbar
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