[issue22766] collections.Counter's in-place operators should return NotImplemented for unsupported types
Ethan Furman
report at bugs.python.org
Wed Nov 5 17:04:33 CET 2014
Ethan Furman added the comment:
Raymond declared:
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> Let's be clear. These are duck-typed methods. A type check is inappropriate.
> Anything with o.items() is allowed regardless of type.
Wikipedia explains (http://en.wikipedia.org/wiki/Duck_typing):
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> In computer programming with object-oriented programming languages, duck typing
> is an alternative to typing. In duck typing, an object's suitability for some
> purpose is determined by the presence of certain methods and properties [...]
I did use an actual 'type' check in one of my exmaples, and that was wrong.
It is possible to do a "duck-type check" with a `hasattr(other, 'items')`.
I don't use Counter myself -- I'll try and find some real-world examples.
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<http://bugs.python.org/issue22766>
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