Type inference error for function taking type argument and returning list of tuple with generic type #16181
Description
Bug Report
mypy prints
Argument 1 to "transform_value" has incompatible type "_T_co"; expected "str" [arg-type]
when calling a function taking type argument and returning a list of tuple with generic type, and using the de-structuring operator to access one of the tuple members:
def transform_value(value: str) -> str:
...
def query_all(signature: type[T], statement: str) -> list[T]:
...
rows = query_all(tuple[str, int], "...")
for row in rows:
first, second = row
value = transform_value(first) # <-- type errorTo Reproduce
See Gist:
from typing import TypeVar
T = TypeVar("T")
def transform_value(value: str) -> str:
return value
def query_all(signature: type[T], statement: str) -> list[T]:
return []
def run_query_1() -> None:
rows = query_all(tuple[str, int], "...")
for row in rows:
first, second = row
value = transform_value(first)
def run_query_2() -> None:
rows = query_all(str, "...")
for row in rows:
value = transform_value(row)Actual Behavior
Revealed type for first in run_query_1 is _T_co rather than str:
Argument 1 to "transform_value" has incompatible type "_T_co"; expected "str" [arg-type]
run_query_2 passes with no error (expected behavior).
Your Environment
Python 3.11.5
mypy 1.5.1 (compiled: yes)
Mypy extension for VS Code
[mypy]
check_untyped_defs = True
disallow_untyped_calls = True
disallow_untyped_decorators = True
disallow_untyped_defs = True
ignore_missing_imports = True
show_column_numbers = True
warn_redundant_casts = True
warn_unused_ignores = True