false negative with underscore on parameter name

Open
#9,447 2 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
tooling

Research direction

Start by running the supplied example with mypy and confirm that the keyword argument is accepted despite the differing parameter names. Trace the override and call-checking paths involved, then add coverage showing the runtime failure is diagnosed or rejected.

Written by the indexing model from the issue text.

Description

bug needs discussion priority-2-low

The following code reports no errors with mypy but will fail at runtime:

class Base:
    def a(self, a: int) -> None: ...

class Derived(Base):
    def a(self, _a: int) -> None:  ...

def foo(b: Base) -> None:
    b.a(a=1)

foo(Derived())
Dominant language
Python
Stars
20.6k
Forks
3.3k
Avg merge
1d 18h
Merged PRs (30d)
54

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/mypy

All issues in python/mypy

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.