[issue45081] dataclasses that inherit from Protocol subclasses have wrong __init__

[Ian Good]

Ian Good <icgood at gmail.com> added the comment:

I believe this was a deeper issue that affected all classes inheriting Protocol, causing a TypeError on even the most basic case (see attached):

Traceback (most recent call last):
  File "/.../test.py", line 14, in <module>
    MyClass()
  File "/.../test.py", line 11, in __init__
    super().__init__()
  File "/usr/local/Cellar/python at 3.9/3.9.7/Frameworks/Python.framework/Versions/3.9/lib/python3.9/typing.py", line 1083, in _no_init
    raise TypeError('Protocols cannot be instantiated')
TypeError: Protocols cannot be instantiated


This was a new regression in 3.9.7 and seems to be resolved by this fix. The desired behavior should be supported according to PEP 544: https://www.python.org/dev/peps/pep-0544/#explicitly-declaring-implementation

----------
nosy: +icgood
Added file: https://bugs.python.org/file50277/test.py

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45081>
_______________________________________