Class scope name resolution issue
Open
Nobody has claimed this yet.
bug
good-second-issue
priority-2-low
topic-runtime-semantics
topic-variable-scope
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Example courtesy of @gvanrossum , based on https://twitter.com/gvanrossum/status/1354305179244392453
While Python's behaviour is surprising, mypy should match it.
from typing import *
x: Optional[int] = None
y: Optional[int] = None
def f() -> None:
x = 1
y = 1
class C:
reveal_type(x) # Incorrectly reveals int, should be Optional[int]
reveal_type(y) # Correctly reveals int
x = 2
I also found https://bugs.python.org/issue24129 interesting. Thanks, ilevkivskyi!
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 by running the issue's Python example through mypy and comparing the two reveal_type results. Trace the class-scope name-resolution logic that handles x and y; done means x is revealed as Optional[int] while y remains int, matching Python's behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100