Replacing methods without subclassing
xtian at toysinabag.com
Mon Jan 27 06:19:33 CET 2003
Aum <spam-me at no-thanks.com> wrote in message news:<2_MY9.47989$F63.1032275 at news.xtra.co.nz>...
> Thanks all the same, but some kind soul on OPN #python told me a much
> simpler way, which I post for benefit of others looking for similar.
> import new
> def setevhandler(self, func):
> Assigns a new event handler function to the class (or subclass)
> instance. This provides an alternative to subclassing.
> cls = self.__class__
> if type(func) is not types.FunctionType:
> raise MyNotFunctionError
> self.handleevent = new.instancemethod(func, self, cls)
That is simpler, but type-checking (the "if type(func)" line) is
almost always a bad idea, preventing potentially useful polymorphism.
In this case you'll be stopping people from passing a class with a
__call__ magic method, or a bound method from another instance. And
although I can't think of a good reason someone might want to do that,
I'm sure that the clever people here can. :)
A way of doing the same thing, which follows the Python idiom of
"checking the interface, rather than the type," would be to use the
def setevhandler(self, func):
Assigns a new event handler function to the class (or
instance. This provides an alternative to subclassing.
cls = self.__class__
if not callable(func):
self.handleevent = new.instancemethod(func, self, cls)
(Another tip you might find useful is being able to specify the
handler's name (if you want to attach multiple handlers to one
instance). This would be done by adding a name parameter, and then
changing the last line of the function to:
setattr(self, name, new.instancemethod(func, self, cls))
Sorry if you already know this!)
More information about the Python-list