False-positive due to missing type narrowing in isinstance of TypeVar #15235
Description
isnistance on a TypeVared variabled does not correctly narrow the type.
To Reproduce
from typing import TypeVar, Union
T = TypeVar("T", bound=Union["A", "B"])
# Imagine fun being used in a class templated on T
def fun(t: T) -> None:
if isinstance(t, A):
print("t is an A: do not print(foo)")
else:
print("t must be a B: it is safe to print(foo)")
# > bug.py:13: error: Item "A" of the upper bound "Union[A, B]" of type variable "T" has no attribute "foo" [union-attr]
print(t.foo)
class A:
...
class B:
foo = 0
fun(A())
fun(B())Expected Behavior
No error
Actual Behavior
bug.py:13: error: Item "A" of the upper bound "Union[A, B]" of type variable "T" has no attribute "foo" [union-attr]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used:
mypy 1.3.0 (compiled: yes) - Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.11.2
python bug,py:
t is an A: do not print(foo)
t must be a B: it is safe to print(foo)
0