I would like to define two types Shape and Square. Here Square is a subclass of Shape.
Shape = NewType('Shape', tuple[int, int])
Square = NewType('Square', Shape)
def square_area(sh: Square) -> int:
a, b = sh
return a * b
def shape_area(sh: Shape) -> int:
a, b = sh
return a * b
I would define an additional type SquareCalculator as follows:
SquareCalculator = NewType('Calculator', Callable[[Square], int])
def get_calc() -> SquareCalculator:
return square_area
The above code leads to the following errors in mypy:
newtyp.py:10: error: String argument 1 "Calculator" to NewType(...) does not match variable name "SquareCalculator"
newtyp.py:13: error: Incompatible return value type (got "Callable[[Square], int]", expected "SquareCalculator")
Found 2 errors in 1 file (checked 1 source file)
Is there a way around this? Note that I would like to maintain the difference in Shape and Square to ensure type-checking catches errors when they are inter-changed.
SquareCalculator should be a type alias, not a newtype, otherwise you need to use typing.cast.
Current syntax:
from typing import TypeAlias
from collections.abc import Callable
SquareCalculator: TypeAlias = Callable[[Square], int]
Python 3.12 syntax:
from collections.abc import Callable
type SquareCalculator = Callable[[Square], int]