On Wed, 10 Mar 2010 08:12:14 -0500, Neal Becker wrote:
> Want to switch __call__ behavior. Why doesn't this work? What is the
> correct way to write this?
>
> class X (object):
> def __init__(self, i):
> if i == 0:
> def __call__ (self):
> return 0
> else:
> def __call_ (self):
> return 1
Others have already pointed out that there are two reasons that won't
work:
(1) you define __call__ as a local variable of the __init__ method which
then disappears as soon as the __init__ method completes; and
(2) special methods like __call__ are only called on the class, not the
instance, so you can't give each instance its own method.
Perhaps the best way to solve this is to use delegation:
def zero_returner():
return 0
def one_returner():
return 1
class X (object):
def __init__(self, i):
if i == 0:
self.func = zero_returner
else:
self.func = one_returner
def __call__(self, *args, **kwargs):
return self.func(*args, **kwargs)
zero_returner and one_returner can be any callable object, not
necessarily a function.
Of course, all this assumes that your solution isn't even simpler:
class X (object):
def __init__(self, i):
self.i = i
def __call__(self):
return self.i
but I assume if it was that simple, you would have done that already.
--
Steven
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