[issue23990] Callable builtin doesn't respect descriptors

[Ionel Cristian Mărieș]

Ionel Cristian Mărieș added the comment:

On Sat, Apr 18, 2015 at 7:23 PM, Ethan Furman <rep...@bugs.python.org>
wrote:

>
>   class GenericProxy:
>       def __init__(self, proxied):
>           self.proxied = proxied
>       # in case proxied is an __iter__ iterator
>       @property
>       def __iter__(self):
>           if not hasattr(self.proxied, '__iter__'):
>               raise AttributeError
>           else:
>               return self
>       @property
>       def __next__(self):
>           if not hasattr(self.proxied, '__next__'):
>               raise AttributeError
>           else:
>               return next(self.proxied)

​Unfortunately y​our implementation is incorrect as you forgot to that the
property needs to return a function. This is a correct implementation that
works as expected (in the sense that *iter does in fact honor the
descriptor protocol)*:

class GenericProxy:
>     def __init__(self, proxied):
>         self.proxied = proxied
>     # in case proxied is an __iter__ iterator
>     @property
>     def __iter__(self):
>         if not hasattr(self.proxied, '__iter__'):
>             raise AttributeError
>         else:
>             return *lambda:* self
>     @property
>     def __next__(self):
>         if not hasattr(self.proxied, '__next__'):
>             raise AttributeError
>         else:
>             return *lambda: *next(self.proxied)
>

​The iter machinery doesn't "grab values and call them", you've
misinterpreted the error.​

Thanks,
-- Ionel Cristian Mărieș, http://blog.ionelmc.ro

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<http://bugs.python.org/issue23990>
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