[Python-Dev] Dinamically set __call__ method

Ethan Furman ethan at stoneleaf.us
Tue Nov 4 19:23:50 CET 2014


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Try asking on Python List.

(forwarding...)

On 11/04/2014 08:52 AM, Roberto Martínez wrote:
>
> I am trying to replace dinamically the __call__ method of an object using setattr.
> Example:
>
> $ cat testcall.py
> class A:
>      def __init__(self):
>          setattr(self, '__call__', self.newcall)
>
>      def __call__(self):
>          print("OLD")
>
>      def newcall(self):
>          print("NEW")
>
> a=A()
> a()
>
> I expect to get "NEW" instead of "OLD", but in Python 3.4 I get "OLD".
>
> $ python2.7 testcall.py
> NEW
> $ python3.4 testcall.py
> OLD
>
> I have a few questions:
>
> - Is this an expected behavior?
> - Is possible to replace __call__ dinamically in Python 3? How?

In 2.7 that would be a classic class, about which I know little.

In 3.x you have a new class, one which inherits from 'object'.  When you replace __call__ you need to replace it the 
class, not on the instance:

   setattr(__self__.__class__, self.newcall)

--
~Ethan~



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