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Re: [Python-Dev] Dinamically set __call__ method

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Ethan Furman wrote:
>>
>>> On 11/06/2014 10:59 PM, dieter wrote:
>>>
>>>> A possibility to get the original approach implemented looks like:
>>>>
>>>>     make "__call__" a descriptor on the class which looks up the real
>>>>     method on the instance.
>>>
>>> This still wouldn't get the signatrue correct, though.
>>
>> Why not? Once the descriptor is resolved, you get the final
>> instance method - with the correct signature.
> 
> Hmmm... well, it wouldn't be correct on a class lookup, but, yeah, it 
> would be correct for an instance lookup -- and maybe that's good enough 
> for the OP.

Seems to depend on how you get hold of the object you're
inspecting the signature of. I did an experiment:

   class C(object):

   @property
     def __call__(self):
       return self.call

   def f(x, y):
     print("Called f with %s, %s" % (x, y))

   c = C()
   c.call = f
   c(17, 42)

prints:
   Called f with 17, 42

This works too:

   import inspect
   print(inspect.getargspec(c.__call__))

prints:
   ArgSpec(args=['x', 'y'], varargs=None, keywords=None, defaults=None)

But

   print(inspect.getargspec(c))

doesn't work:

   TypeError: <__main__.C object at 0x479250> is not a Python function

(BTW, I'm actually surprised that this technique makes c callable.
There must be more going on that just "look up __call__ in the class
object", because evaluating C.__call__ just returns the descriptor
and doesn't invoking the descriptor mechanism.)

-- 
Greg

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Re: [Python-Dev] Dinamically set __call__ method Ethan Furman <ethan@stoneleaf.us> - 2014-11-04 11:12 -0800
  Re: [Python-Dev] Dinamically set __call__ method John Ladasky <john_ladasky@sbcglobal.net> - 2014-11-06 12:21 -0800
    Re: [Python-Dev] Dinamically set __call__ method dieter <dieter@handshake.de> - 2014-11-07 07:59 +0100
    Re: [Python-Dev] Dinamically set __call__ method Ethan Furman <ethan@stoneleaf.us> - 2014-11-07 04:58 -0800
    Re: [Python-Dev] Dinamically set __call__ method dieter <dieter@handshake.de> - 2014-11-08 07:50 +0100
    Re: [Python-Dev] Dinamically set __call__ method Ethan Furman <ethan@stoneleaf.us> - 2014-11-08 11:49 -0800
      Re: [Python-Dev] Dinamically set __call__ method Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-09 11:31 +1300
        Re: [Python-Dev] Dinamically set __call__ method Ethan Furman <ethan@stoneleaf.us> - 2014-11-08 19:27 -0800
          Re: [Python-Dev] Dinamically set __call__ method Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-10 00:38 +1300
            Re: [Python-Dev] Dinamically set __call__ method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-10 00:14 +1100
            Re: [Python-Dev] Dinamically set __call__ method Ethan Furman <ethan@stoneleaf.us> - 2014-11-09 12:16 -0800
        Re: [Python-Dev] Dinamically set __call__ method Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-11 00:43 -0700
        Re: [Python-Dev] Dinamically set __call__ method Fabio Zadrozny <fabiofz@gmail.com> - 2014-11-12 13:33 -0200
          Re: [Python-Dev] Dinamically set __call__ method Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-13 17:20 +1300
            Re: [Python-Dev] Dinamically set __call__ method Fabio Zadrozny <fabiofz@gmail.com> - 2014-11-13 11:38 -0200
        Re: [Python-Dev] Dinamically set __call__ method Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-12 11:58 -0700

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