Mypy false positive for `converter` class attribute in `logging.Formatter` class.
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Description
Bug Report
Mypy false positive: Mypy thinks that setting the converter class attribute for a subclass of logging.Formatter to something like time.gmtime is wrong.
To Reproduce
class UTCFormatter(logging.Formatter):
"""An exact match for the `logging.Formatter` class, except that it logs the time in UTC."""
converter = time.gmtime
Expected Behavior
No error, since time.gmtime is annotated as def gmtime(seconds: float | None = None, /) -> struct_time: ... and the converter attribute is annotated as converter: Callable[[float | None], struct_time].
Actual Behavior
logger.py:45: error: Incompatible types in assignment (expression has type "Callable[[], struct_time]", base class "Formatter" defined the type as "Callable[[float | None], struct_time]") [assignment]
Your Environment
- Mypy version used: 1.16.0 (compiled: yes)
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.13.4 (on Linux)
By the way, this issue didn't exist in my Python3.12 environment with an older version of mypy installed, but I don't have access to that environment right now so I can't provide which mypy version it had.
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
No repository file or test is named. Reproduce the UTCFormatter example with mypy 1.16.0 on Python 3.13.4, then locate handling of subclass assignments to callable class attributes and add a regression test; done means no assignment error for time.gmtime while incompatible overrides remain diagnosed.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100