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[Python-Dev] PEP 544: Protocols - second round

Ivan Levkivskyi levkivskyi at gmail.com
Thu Jun 22 17:53:20 EDT 2017 
On 22 June 2017 at 10:44, Markus Wissinger <markus.wissinger at gmail.com>
wrote:

> I have to admit I am not happy with separating the concepts of 'runtime'
> and 'static' types as implied by pep544.
>

This is not something new, already PEP 483 makes a clear distinction
between types (a static concept) and classes (a runtime concept).


> Failing isinstance/issubclass calls for protocols would hurt there. I
> understand that any type checker code that could provide isinstance
> functionality for pep544 protocols would rely on method signatures that my
> hint generator is just producing.
>

isinstance(obj, T) and issubclass(Cls, T) already fail if T is a
subscripted generic like List[int], so that again nothing new here. To
check runtime subtyping with such types one can write a third party
introspection tool based on typing_inspect package on PyPI (which
potentially might in future become an official wrapper for currently
internal typing API).

--
Ivan
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