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.
Advertisement
Answer
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)