`dataclass`es that inherit from `Protocol` subclasses have wrong `__init__`

[julianfortune]

I believe bpo-44806: Fix __init__ in subclasses of protocols has caused a regression when using a Dataclass.

In Python 3.9.7, a dataclass that inherits from a subclass of typing.Protocol (i.e., a user-defined protocol), does not have the correct __init__.

Demonstration

from dataclasses import dataclass
from typing import Protocol

class P(Protocol):
    pass

@dataclass
class B(P):
    value: str

print(B("test"))

In 3.9.7:

Traceback (most recent call last):
  File "test.py", line 11, in <module>
    print(B("test"))
TypeError: B() takes no arguments

In 3.9.6:

B(value='test')

Affected Projects

• dbt

[srittau]

Please report this at bugs.python.org.

[julianfortune]

Thanks for the fast response.

Python Issue

[AthenaCaesura]

This bug was solved in python 3.10, however the issue still remains for 3.9.7.

Is there any workaround that one could use instead of upgrading? Since 3.9.7 is the last version of 3.9 saying we don't support 3.9.7 is more or less the same as saying we don't support 3.9.

I would like to keep the frozen option if at all possible.

[hauntsaninja]

Python 3.9.10 is the latest release of 3.9 and presumably contains python/cpython#28132

(this also isn't the right issue tracker for further discussion of this, please redirect to bugs.python.org)