Andrew Koenig wrote:
> I note in PEP 3000 the proposal to remove callable(), with the comment "just
> call the object and catch the exception."
>
> I think that's a bad idea, because it takes away the ability to separate the
> callability test from the first call. As a simple example, suppose you're
> writing a function that you expect to be given a function as one of its
> arguments:
>
> def foo(bar, fun):
> assert callable(fun)
> # ...
>
> It might be that foo doesn't actually call fun until much later.
> Nevertheless, from a testing viewpoint, it would be better to detect the
> error immediately of passing something that can't be called.
>
> If you didn't have callable, how would you write this example?
How about changing callable's semantics to something like the following?:
def callable(obj, attr="__call__"):
if attr != "__call__":
obj = getattr(obj, attr, None)
return getattr(obj, "__call__", None) is not None
Test for callability:
assert callable(obj)
Test for hashability:
assert callable(obj, "__hash__")
Test for iterability:
assert callable(obj, "__iter__")
Test for a context manager:
assert callable(obj, "__enter__") and callable(obj, "__exit__")
Cheers,
Nick.
--
Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
---------------------------------------------------------------
http://www.boredomandlaziness.org
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