类型提示以返回类型为参数的 function

Question

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.

Answer 1

Have a look at Generics , especially TypeVar . You can do something like this:

from typing import TypeVar, Any

T = TypeVar("T")

def mycoerce(data: Any, ret_type: T) -> T:
    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)