It's sometimes useful to be able to use an existing callable as a method of a
new class. If the callable is a real function, this is easy. You just
including the following line in the class definition:
method = some_callable
However, callable objects without a function-like __get__ method can't be used
that way. So, to avoid a dependency on an implementation detail of
some_callable (i.e. whether or not it is a true function object), you have to
write:
def method():
return some_callable()
(and you can lose useful metadata in the process!)
However, if you're adding a callable as a class method or static method, there
is OOWTDI:
method = classmethod(some_callable)
method = staticmethod(some_callable)
It would be nice if there was a similar mechanism for normal instance methods
as well:
method = function(some_callable)
This came up during the PEP 343 implementation - "context =
contextlib.closing" is a tempting thing to write in order to provide a
"x.context()" method for use in a with statement, but it doesn't actually work
properly (because closing is a class, not a function).
Similarly, you can't create a method simply by applying functools.partial to
an existing function - the result won't have a __get__ method, so it will be
treated like a normal attribute instead of as an instance method.
Cheers,
Nick.
--
Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia
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