class variables for subclasses tuple

alainpoint at yahoo.fr alainpoint at yahoo.fr
Wed Mar 8 11:06:40 CET 2006


Peter Otten wrote:
> alainpoint at yahoo.fr wrote:
>
> > Point.x=0 leads to having p.x==0
> > It seems not possible to have class variables and instance variable
> > having the same name and yet different values.
>
> A quick check:
>
> >>> class T(tuple):
> ...     class __metaclass__(type):
> ...             x = property(lambda cls: 0)
> ...     x = property(lambda self: self[0])
> ...
> >>> t = T("abc")
> >>> t.x
> 'a'
> >>> T.x
> 0
>
> So possible it is. Come back if you're stuck generalizing the above.
>
> Peter

Thanks for your magic answer.
But i am not so good at magic ;-)
If i want to generalize to a arbitrary number of variables, i got
syntax errors.
Within a class, you can only method/class definitions and assignments.
It is therefore difficult to do something like:
	for idx, attr_name in enumerate(attribute_names):
		setattr(__metaclass__,attr_name, property(lambda cls:idx)
	for idx, attr_name in enumerate(attribute_names):
		setattr(T,attr_name, property(lambda self:self[idx])

Alain




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