[New-bugs-announce] [issue47237] Inheritance from Protocol with property in dataclass makes them non-instantiatable

[Daniel Draper]

New submission from Daniel Draper <Germandrummer92 at 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

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue47237>
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