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changing __call__ on demand

Stefan Behnel stefan.behnel-n05pAM at web.de
Sun Feb 13 11:49:13 EST 2005 
Hi!

This somewhat puzzles me:

Python 2.4 (#1, Feb  3 2005, 16:47:05)
[GCC 3.3.4 (pre 3.3.5 20040809)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

.>>> class test(object):
...   def __init__(self):
...     self.__call__ = self.__call1
...   def __call1(self):
...     print 1
...   def __call__(self):
...     print 2
...
.>>> t = test()
.>>> t()
2

If I take out the __call__ method completely and only set it in __init__, I 
get a TypeError saying that test is not callable.

I want to use this in order to provide different implementations based on the 
object configuration. Calculating the right function to call is non-trivial 
and calls are frequent, so I want to change __call__ in order to run the right 
function directly.

I know, I could use another level of indirection:

def __call__(self):
   self.the_right_method()

and then set the_right_method accordingly, but I find that somewhat 
sub-optimal. Is there a way to change __call__ after class creation?

Stefan
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