Method behavior for user-created class instances

Larry Bates larry.bates at websafe.com`
Tue Jul 15 03:04:14 CEST 2008


crazychimp132 at gmail.com wrote:
> Greetings.
> 
> I am looking for a way to achieve method behavior for a class I
> created. That is, it has a __call__ method,  so can be called like a
> function. But I also want it to be treated as a method when it appears
> in a class body.
> 
> Eg.
> 
> class foo:
>     def __call__(self, inst): pass
> 
> class bar:
>     meth = foo()
> 
> such that bar().meth() will not raise an exception for too few
> arguments (because the inst argument in foo.__call__ is implicitly set
> to the bar instance). I know this has to do with writing the __get__
> method of foo, but I am wondering if there is perhaps some class I can
> just inherit from to get the proper __get__, which behaves identically
> to that of regular Python functions. The need for this arises out of
> the implementation of a function decorator as a class.
> 
> Thanks.

While it is not clear "why" you would want this, I believe this works.
If not, take a look at staticmethods or classmethods, they might work for you.

 >>> class foo(object):
... 	def __call__(self, inst):
... 	    print "foo.__call__", inst
...

 >>> class bar:
... 	def __init__(self):
... 	    self.foo = foo()
... 	    self.meth = self.foo.__call__
...
 >>> b = bar()
 >>> b.meth(1)
foo.__call__ 1

-Larry



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