Sequence rather than list needs to be used to recognise implicit upcasts.
from typing import NewType
from collections.abc import Sequence
TName = NewType("TName", str)
def char_count(name: str) -> int:
return len(name)
def count1(names: list[str]) -> int:
return len(names)
def count2(names: Sequence[str]) -> int:
return len(names)
def main() -> None:
names = [TName("John"), TName("Jane"), TName("Joe")]
# linter happy
print(char_count(names[0]))
# Argument of type "list[TName]" cannot be assigned to parameter "names" of type "list[str]" in function "count1"
# "list[TName]" is incompatible with "list[str]"
# Type parameter "_T@list" is invariant, but "TName" is not the same as "str"
# Consider switching from "list" to "Sequence" which is covariantPylancereportGeneralTypeIssues
print(count1(names))
# linter happy
print(count2(names))