trouble with copy/deepcopy

[Mike Meyer]

Alexander_Zatvornitskiy at p131.f3.n5025.z2.fidonet.org (Alexander Zatvornitskiy) writes:

> ðÒÉ×ÅÔ Marc!
>
> 16 ÍÁÑ 2005 × 22:18, Marc 'BlackJack' Rintsch × Ó×ÏÅÍ ÐÉÓØÍÅ Ë All ÐÉÓÁÌ:
>
>  MR> That clears only one dictionary at class level.  Which is visible on
>  MR> both instances.
>
>  MR> class Distribution:
>  MR>     def __init__(self):
>  MR>         self.__gr_on_transp = dict()
>  MR>         self.__ostatok_m = dict()
>  MR>     ...
>
>  MR> This creates *instance variables* which should be deepcopied
>  MR> without problems.
> Hmm. I don't find definition of "class variable" in manual. I try to test it on
> such a simple test and find that such variable is NOT shared between copies:

Actually, it is shared - but only for reference. If you assign to it,
you'll create an instance variable of the same name. As Peter
explained, if you remove the instance variable, the class variable
becomes visible again. Try this:

py> class C:
...   q = []
... 
py> c1 = C()
py> c2 = C()
py> c3 = C()
py> c1.q.append(1)
py> c2.q.append(2)
py> c3.q.append(3)
py> c1.q, c2.q, c3.q
([1, 2, 3], [1, 2, 3], [1, 2, 3])
py> 

    <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
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