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

[Ian Good]

Ian Good  added the comment:

Julian,

That is certainly a workaround, however the behavior you are describing is 
inconsistent with PEP-544 in both word and intention. From the PEP:

> To explicitly declare that a certain class implements a given protocol, it 
> can be used as a regular base class.

It further describes the semantics of inheriting as "unchanged" from a "regular 
base class". If the semantics are "unchanged" then it should follow that 
super().__init__() would pass through the protocol to the object.__init__, just 
like a "regular base class" would if it does not override __init__.

Furthermore, the intention of inheriting a Protocol as described in the PEP:

> Static analysis tools are expected to automatically detect that a class 
> implements a given protocol. So while it's possible to subclass a protocol 
> explicitly, it's not necessary to do so for the sake of type-checking.

The purpose of adding a Protocol sub-class as an explicit base class is thus 
only to improve static analysis, it should *not* to modify the runtime 
semantics.

Consider the case where a package maintainer wants to enhance the flexibility 
of their types by transitioning from using an ABC to using structural 
sub-typing. That simple typing change would be a breaking change to the package 
consumers, who must now remove a super().__init__() call.

Ian

--

___
Python tracker 

___
___
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__

[Julian Fortune]

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 

___
___
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__

[Ian Good]

Ian Good  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 
MyClass()
  File "/.../test.py", line 11, in __init__
super().__init__()
  File 
"/usr/local/Cellar/python@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 

___
___
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__

[Łukasz Langa]

Change by Łukasz Langa :


--
versions: +Python 3.10, Python 3.11

___
Python tracker 

___
___
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__

[miss-islington]

miss-islington  added the comment:


New changeset 79e9f5a58427c73dc546cb571819d50defe2e14f by Miss Islington (bot) 
in branch '3.10':
bpo-45081: Fix __init__ method generation when inheriting from Protocol 
(GH-28121)
https://github.com/python/cpython/commit/79e9f5a58427c73dc546cb571819d50defe2e14f


--

___
Python tracker 

___
___
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__

[Julian Fortune]

Change by Julian Fortune :


--
stage: patch review -> resolved
status: open -> closed

___
Python tracker 

___
___
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__

[Łukasz Langa]

Łukasz Langa  added the comment:


New changeset 98eb40828af97760badfa7b8ff84bd4f7a079839 by Miss Islington (bot) 
in branch '3.9':
bpo-45081: Fix __init__ method generation when inheriting from Protocol 
(GH-28121) (GH-28132)
https://github.com/python/cpython/commit/98eb40828af97760badfa7b8ff84bd4f7a079839


--

___
Python tracker 

___
___
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__

[miss-islington]

Change by miss-islington :


--
nosy: +miss-islington
nosy_count: 8.0 -> 9.0
pull_requests: +26569
pull_request: https://github.com/python/cpython/pull/28131

___
Python tracker 

___
___
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__

[miss-islington]

Change by miss-islington :


--
pull_requests: +26570
pull_request: https://github.com/python/cpython/pull/28132

___
Python tracker 

___
___
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__

[Łukasz Langa]

Łukasz Langa  added the comment:


New changeset 0635e201beaf52373f776ff32702795e38f43ae3 by Yurii Karabas in 
branch 'main':
bpo-45081: Fix __init__ method generation when inheriting from Protocol 
(GH-28121)
https://github.com/python/cpython/commit/0635e201beaf52373f776ff32702795e38f43ae3


--

___
Python tracker 

___
___
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__

[Ken Jin]

Change by Ken Jin :


--
nosy: +kj, lukasz.langa, serhiy.storchaka

___
Python tracker 

___
___
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__

[Yurii Karabas]

Change by Yurii Karabas <1998uri...@gmail.com>:


--
keywords: +patch
nosy: +uriyyo
nosy_count: 4.0 -> 5.0
pull_requests: +26562
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/28121

___
Python tracker 

___
___
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__

[Shrikant Narasimhan]

Change by Shrikant Narasimhan :


--
nosy: +shrik

___
Python tracker 

___
___
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__

[Edgar Ramírez]

Change by Edgar Ramírez :


--
nosy: +edgarrmondragon

___
Python tracker 

___
___
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__

[Eric V. Smith]

Change by Eric V. Smith :


--
nosy: +eric.smith

___
Python tracker 

___
___
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__

[Julian Fortune]

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

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com