Is there a way to type hint a function that takes as argument its return type? I naively tried to do this:
# NOTE:
# This code does not work!
#
# If I define `ret_type = TypeVar("ret_type")` it becomes syntactically
# correct, but type hinting is still broken.
#
def mycoerce(data: Any, ret_type: type) -> ret_type
return ret_type(data)
a = mycoerce("123", int) # desired: a type hinted to int
b = mycoerce("123", float) # desired: b type hinted to float
but it doesn't work.
Have a look at Generics, especially TypeVar. You can do something like this:
from typing import TypeVar, Callable
R = TypeVar("R")
D = TypeVar("D")
def mycoerce(data: D, ret_type: Callable[[D], R]) -> R:
return ret_type(data)
a = mycoerce("123", int) # desired: a type hinted to int
b = mycoerce("123", float) # desired: b type hinted to float
print(a, b)