[Python-Dev] PEP 544: Protocols - second round (original) (raw)

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).

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