[issue45081] dataclasses that inherit from Protocol subclasses have wrong __init__
Julian Fortune added the comment: Ian, `MyProtocol` does not provide an `__init__()`, and thus ``` super().__init__() ``` is calling the `__init__()` from `Protocol`. This results in the `TypeError`. Simply remove `super().__init__()` to resolve your issue. This behavior was changed in https://github.com/python/cpython/pull/27545 (see `Lib/typing.py:1384`); I don't see what you are reporting as a regression, I see it as correct behavior that I would expect. Apologies if you feel differently. Cheers, Julian -- ___ Python tracker <https://bugs.python.org/issue45081> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue45081] dataclasses that inherit from Protocol subclasses have wrong __init__
Change by Julian Fortune : -- stage: patch review -> resolved status: open -> closed ___ Python tracker <https://bugs.python.org/issue45081> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue45081] dataclasses that inherit from Protocol subclasses have wrong __init__
New submission from Julian Fortune :
I believe [`bpo-44806: Fix __init__ in subclasses of
protocols`](https://github.com/python/cpython/pull/27545) 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
```python
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`:
```shell
Traceback (most recent call last):
File "test.py", line 11, in
print(B("test"))
TypeError: B() takes no arguments
```
In `3.9.6`:
```shell
B(value='test')
```
### Affected Projects
- [dbt](https://github.com/dbt-labs/dbt/issues/3843)
--
components: Library (Lib)
messages: 400868
nosy: julianfortune
priority: normal
severity: normal
status: open
title: dataclasses that inherit from Protocol subclasses have wrong __init__
type: behavior
versions: Python 3.9
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