Common type in container is determined using constructor args
Open
Nobody has claimed this yet.
bug
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Bug Report
To Reproduce
from typing import Type, List
class NonLiskovChild(Exception):
"""Does not match Exception.__init__() signature"""
def __init__(self, _some_other_arg: object) -> None:
super().__init__()
types1 = [TypeError, ValueError]
reveal_type(types1)
# Revealed type is 'builtins.list[def (*args: builtins.object) -> builtins.Exception]'
types2 = [TypeError, NonLiskovChild]
reveal_type(types2)
# Revealed type is 'builtins.list[builtins.type*]'
# When explicitly setting the type, mypy accepts NonLiskovChild as an Exception subtype:
types3: List[Type[Exception]] = [TypeError, NonLiskovChild]
reveal_type(types3)
# Revealed type is 'builtins.list[Type[builtins.Exception]]'
Expected Behavior
The lowest common type should be determined by inheritance, not with __init__() signature matching.
Otherwise stdlib classes like CalledProcessError do not work correctly, e.g. in this example:
import pytest
from subprocess import CalledProcessError
with pytest.raises((TypeError, CalledProcessError)) as exc_info:
pass
# error: Need type annotation for "exc_info"
# error: Argument 1 to "raises" has incompatible type "Tuple[Type[TypeError], Type[CalledProcessError]]"; expected "Union[Type[<nothing>], Tuple[Type[<nothing>], ...]]"
Your Environment
- Mypy version used: 0.910
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.8.10
- Operating system and version: Windows 10
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 reproducing the two reveal_type examples and the pytest.raises case from the issue. Trace how the container's common type is inferred from the class constructors, then verify that the reported Exception subclasses produce the expected inferred types and no incompatible-argument errors.
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
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100