New submission from Daniel Draper <germandrumme...@gmail.com>:
Hi, According to https://peps.python.org/pep-0544/#explicitly-declaring-implementation it should be possible to explicitly inherit from Protocols. This however breaks the dataclass constructor when using the @property decorator in the protocol, see this example: ```python from typing import Protocol from dataclasses import dataclass class SomeProtocol(Protocol): @property def some_value(self) -> str: ... @dataclass class SomeDataclasss(SomeProtocol): some_value: str if __name__ == '__main__': a = SomeDataclasss(some_value="value") # this crashes with AttributeError: can't set attribute 'some_value' ``` The pattern of @property in the protocol is one taken from the mypy docs (see https://mypy.readthedocs.io/en/stable/protocols.html#recursive-protocols for example). When removing the explicit inheritiance mypy also correctly typechecks the dataclass implementation when doing something like, only the explicit inheritance seems to fail in python ```python a: SomeProtocol = SomeDataclass() ``` ---------- components: Library (Lib) messages: 416846 nosy: Germandrummer92 priority: normal severity: normal status: open title: Inheritance from Protocol with property in dataclass makes them non-instantiatable type: behavior versions: Python 3.10 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue47237> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
