Suppose I want to write a generic class using mypy, but the type argument for the class is itself a generic type. For example:
from typing import TypeVar, Generic, Callable
A = TypeVar("A")
B = TypeVar("B")
T = TypeVar("T")
class FunctorInstance(Generic[T]):
def __init__(self, map: Callable[[Callable[[A], B], T[A]], T[B]]):
self._map = map
def map(self, x: T[A], f: Callable[[A], B]) -> T[B]:
return self._map(f, x)
When I try to call mypy in the definition above I get an error:
$ mypy typeclasses.py
typeclasses.py:9: error: Type variable "T" used with arguments
typeclasses.py:12: error: Type variable "T" used with arguments
I tried adding constraints to the T TypeVar's definition but failed to make this work. Is it possible to do this?
Currently, as of writing, the mypy project does not support higher-kinded types. See the following github issue: