Should we always prohibit "abstract" attributes?

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start with the issue examples and the existing comment discussion, which raise whether abstract attributes should be prohibited only for protocols or also for normal ABCs. A contribution would need an agreed policy and corresponding behavior for both cases; the issue names no files or tests to run.

Written by the indexing model from the issue text.

Description

needs discussion topic-protocols topic-runtime-semantics

Currently, instantiating explicit subclasses of protocols with "abstract" attributes is prohibited:

class P(Protocol):
    x: int  # Note, no r.h.s.

class C(P):
    pass
class D(P):
    def __init__(self) -> None:
        self.x = 42

C()  # E: Cannot instantiate abstract class 'C' with abstract attribute 'x'
D()  # OK

This is feature appeared with little discussion, in particular should this be specific only to protocols or also to "normal" ABCs?

Dominant language
Python
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Merged PRs (30d)
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