__call__ considered harmful or indispensable?

[Diez B. Roggisch]

skip at pobox.com schrieb:
> I don't personally use __call__ methods in my classes, but I have
> encountered it every now and then here at work in code written by other
> people.  The other day I replaced __call__ with a more obvious method name,
> so now instead of executing
> 
>     obj(foo, bar, baz)
> 
> the code in question is
> 
>     obj.execute(foo, bar, baz)
> 
> In this case there was a bug.  Depending on inputs, sometimes obj
> initialized to a class, sometimes an instance of that class.  (I fixed that
> too while I was at it.)  The problem was that the use of __call__ obscured
> the underlying bug by making the instance as well as the class callable.
> 
> In this particular case it was clearly unnecessary and just obfuscated the
> code.  I'm wondering, are there some general cases where __call__ methods of
> a user-defined class are simply indispensable?

Thanks to closures and bound methods, I don't think that there is  a 
case where you can't "fake" the missing __call__ at least when it comes 
to call-backs. So in the end, you can always work around that. But if 
you don't need to...

Se the gnosis multimethods for an implementation that makes sensible use 
of the __call__-operator in my opinion.

diez