Sunday, October 25, 2020

Python generic methods/functions

This is something minor but that could use with some more attention. In C# you can use generics with methods so that if a function needs to use a generic type which can be different with different calls then you can simply do this:
class C {
    T getValue() {
Now Python has type hints which are used by the program mypy, but I was having trouble finding how to do generic methods with it. The problem is that generic method examples shown require you to pass in a parameter with the generic type. But if the type is not used in the parameters but only in the return, as shown in the C# example above, then you'd be in trouble. The solution is to pass the type itself as a parameter, in the same way that the C# example above does but as a parameter instead of outside the parameter list. It is shown here but not as a generic function.
from typing import TypeVar, Type

T = TypeVar('T')

class C:
    def get_value(return_type: Type[T]) -> T: