change property after inheritance

Maric Michaud maric at aristote.info
Wed Sep 6 17:44:42 CEST 2006


Le mercredi 06 septembre 2006 16:33, David Isaac a écrit :
> Suppose a class has properties and I want to change the
> setter in a derived class. If the base class is mine, I can do this:
> http://www.kylev.com/2004/10/13/fun-with-python-properties/
> Should I? (I.e., is that a good solution?)

Why not ? This ontroduce the notion of public getter a la C++/Java while the 
property is overloadable by itself (as below), but it's correct design IMHO.

> And what if I cannot change the base class?
> How to proceed then?

Like that :

In [44]: class a(object) :
   ....:     p=property(lambda s : getattr(s, '_p', None))
   ....:
   ....:

In [46]: class b(a) :
   ....:     p=property(a.p.fget, lambda s, v : setattr(s, '_p', v))
   ....:
   ....:

In [47]: print a().p
None

In [48]: a().p = 5
---------------------------------------------------------------------------
exceptions.AttributeError                            Traceback (most recent 
call last)

/home/maric/<ipython console>

AttributeError: can't set attribute

In [49]: ib=b()

In [50]: print ib.p
None

In [51]: ib.p = 5

In [52]: print ib.p
5

In [53]: ib._p
Out[53]: 5


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Maric Michaud
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