surprising interaction between function scope and class namespace

Stefan Behnel stefan_ml at behnel.de
Mon Aug 15 11:50:58 CEST 2011


Stefan Behnel, 15.08.2011 11:33:
> I just stumbled over this:
>
>  >>> A = 1
>  >>> def foo(x):
>  ...     A = x
>  ...     class X:
>  ...         a = A
>  ...     return X
>  ...
>  >>> foo(2).a
>  2
>  >>> def foo(x):
>  ...     A = x
>  ...     class X:
>  ...         A = A
>  ...     return X
>  ...
>  >>> foo(2).A
>  1
>
> Works that way in Py2.7 and Py3.3.
>
> I couldn't find any documentation on this, but my *guess* about the
> reasoning is that the second case contains an assignment to A inside of the
> class namespace, and assignments make a variable local to a scope, in this
> case, the function scope. Therefore, the A on the rhs is looked up in that
> scope as well. However, this is just a totally hand waving guess.

... and an incorrect one, as it turns out. I think I misinterpreted the 
results the wrong way around. Still:

> Does anyone have a better explanation or know of a place where this
> specific behaviour is documented?

Stefan




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