Incorrect type narrowing for `x in y` pattern when `x` is `type[T]` and `y` is an iterable of class objects
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Description
Bug Report
As the title suggests, if one uses the type_var in (type1, type2, ...) construct instead of issubtype(type_var, (type1, type2, ...), and type_var is generic, mypy struggles with narrowing down the type.
The same bug happens in pyright.
To Reproduce
from typing import TypeVar
T = TypeVar('T')
def func(typ: type[T], input: str) -> T:
if typ in (str, int, float):
return typ(input) # error: Too many arguments for "object" [call-arg]
else:
raise ValueError() # Just for the sake of demonstration
def func(typ: type[T], input: str) -> T:
if issubclass(typ, (str, int, float)):
return typ(input) # No problem!
else:
raise ValueError() # Just for the sake of demonstration
Expected Behavior
Both versions of the type check act the same.
Actual Behavior
Mypy incorrectly throws Too many arguments for "object" [call-arg] error.
Your Environment
- Mypy version used: 1.11.2
- Mypy command-line flags: N/A
- Mypy configuration options from
mypy.ini(and other config files): N/A - Python version used: 3.12 / 3.10
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 running the provided reproducer with mypy and compare the in and issubclass cases. Trace the type-narrowing path for membership checks and add a regression test covering type[T] with an iterable of class objects; done means the typ(input) call is accepted in the in case without weakening the existing behavior.
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
- 38/100