global lists

[Bernd Nawothnig]

On 2005-05-08, andrea crotti wrote:

> I have a little "problem", I don't understand the reason of this:

> a = [10,1,2,3]
> def foo():
>   global a
>   for el in a:
>     el = el*2

Simple data types (as integer) are _not_ implemented as references as
you obviously expected. Instead el is copied by value from each a[n].
Thus you only changed temporary copies.

The whole list instead _is_ a reference. If you write 

b = a
b[0] = 57

a[0] will be effected too.


> This doesn't make any difference, if I do
> def foo():
>   global a
>   a[0] = 4

That should alter a[0].

> But
>
> def foo():
>   global a
>   for n in range(len(a)):
>     a[n] = a[n]*2
>
> Doesn't work either...

It does. Test it again.



Bernd

-- 
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