Consider allowing `@final` methods in Protocols
Open
Nobody has claimed this yet.
feature
topic-final
topic-protocols
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Feature
Allow this:
from typing import Protocol, final
class Sized(Protocol):
len: int
@final
def __len__(self) -> int:
return self.len
Pitch
I get that this is a bit unusual, but I don’t really see any harm that could come from this (as an aside, pyright allows it). My use case is that I’m using Protocols for mixins, and sometimes I want to make sure my mixed-in methods don’t get overwritten.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the reported Python example and compare mypy’s current handling with pyright, which the issue says allows it. Trace the existing Protocol and @final validation paths, then add coverage showing that a final method in a Protocol is accepted and remains protected from overrides.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100