On Saturday 20 February 2010 11:46:42 Diez B. Roggisch wrote:
> Am 20.02.10 17:12, schrieb lallous:
> > Hello
> >
> > How can I do something similar to pure virtual functions in C++ ?
> >
> > Let us consider this:
> >
> > class C1:
> >
> > # Pure virtual
> > def cb(self, param1, param2):
> > """
> > This is a callback
> >
> > @param param1: ...
> > @param param2: ...
> > """
> > raise NotImplementedError, "Implement me"
> >
> > # Implementation w/o a 'cb', thus 'cb' should not be used
> > class C2(C1):
> > def __init__(self):
> > pass
> >
> > # Implementation w/ 'cb', thus 'cb' can be used
> > class C3(C1):
> > def __init__(self):
> > pass
> >
> > def cb(self, param1, param2):
> > print "i am c3 cb"
> >
> > # Dispatcher function that calls 'cb' only if 'cb' is implemented in
> > child classes
> > def dispatcher(c):
> > if hasattr(c, 'cb'):
> > c.cb("Hello", "World")
> >
> > dispatcher(C2())
> > dispatcher(C3())
> >
> > What I want is the ability to have the dispatcher() not to call 'cb'
> > if it was not implemented in one of the child classes.
> >
> > Please advise.
>
> There is nothing more beyond that what you already did. You can raise a
> NotImplementedError for classes that don't implement the method. That's it.
>
> Diez
>
Perhaps you could use an easier-to-ask-forgiveness-than-permission idiom?
def dispatcher(c):
try:
c.cb("Hello", "World")
except NotImplementedError:
pass
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Rami Chowdhury
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