the 'in' operator and class instances

Vinoo vasudevan ee01b092 at ee.iitm.ernet.in
Sun Jun 8 11:02:32 CEST 2003


Hi,
I'm an newbie and have been getting to know Python over the past two weeks.
One of the things I really liked was the 'in' operator. Statements like "key
in dict" or "line in file" are really cool. But this doesn't seem to work for
classes. i.e.

>>> class a:
   def f(self):
      pass

>>> 'f' in a
<Traceback>

Could somebody tell me why class instances don't use in to check for
memebership i.e. something like hasattr(..). I read up on "__contains__" in
the Language Reference. Couldn't python just define a default version of this
for all classes/instances to check for membership. Any class that attaches a
special meaning to membership can of course define its own "__contains__". In
c++ terminology (my __previous__ language :-) ) : can't "object" define a
virtual function "__contains__"? Just a suggestion. Plz let me know if I don't
have a clue of I'm talking about. :-)


Vinoo 






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