[Python-ideas] Discussion: Duck typing with “concepts”

[Ivan Levkivskyi]

I think you may be a bit late. Have you heard about PEP 544?

--
Ivan



On Tue, 22 Jan 2019 at 11:50, James Lu <jamtlu at gmail.com> wrote:

> So here’s an interesting idea, not a proposal yet.
>
> In C++20, a Concept is a list of Boolean expressions with a name that can
> be used in place of a type in a templated (ie type-generic) function.
>
> from typing import Concept
> Iterator = Concept(lambda o: hasattr(o, "__iter__", lambda o: iter(o) !=
> NotImplemented)
> # Concept inheritance
> Iterable = Concept(lambda o: hasattr(o, "__next__"), Iterator)
>
> You could use concepts to define many practical “real-world” duck types.
>
> A concept is like an opt-in duck typing type assertion. Since it’s a part
> of type annotation syntax, assertions can be generated automatically by
> looking at assertions.
>
> You would use a Concept like any other type in type annotations.
>
> Marko, how do you think Concepts might integrate with icontract? (I’m
> imagining overriding an import hook to automatically add contracts to
> functions with concepts.) How frequently do you use duck typing at
> Parquery? How might Concepts affect how often you used duck typing?
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