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dataclasses that inherit from Protocol subclasses have wrong __init__ #883

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julianfortune opened this issue Sep 1, 2021 · 4 comments
Closed

dataclasses that inherit from Protocol subclasses have wrong __init__ #883

julianfortune opened this issue Sep 1, 2021 · 4 comments

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@julianfortune
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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
@srittau
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srittau commented Sep 1, 2021

Please report this at bugs.python.org.

@srittau srittau closed this as completed Sep 1, 2021
@julianfortune
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julianfortune commented Sep 1, 2021 •
edited
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Thanks for the fast response.

Python Issue

@AthenaCaesura
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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
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hauntsaninja commented Feb 17, 2022 •
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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)

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4 participants
@srittau @hauntsaninja @julianfortune @AthenaCaesura