How to declare AnyStr using new type syntax?

Typing
1

When I try

type AnyStr = (str, bytes)

I get

$ mypy --version
mypy 1.19.1 (compiled: yes)

$ mypy huh.py
huh.py:1: error: Invalid type alias: expression is not a valid type  [valid-type]
2

AnyStr is a constrained type variable, not a type alias. You can declare a function, class, or type alias generic over a type variable equivalent to AnyStr as follows:

def concat[AnyStr: (str, bytes)](x: AnyStr, y: AnyStr) -> AnyStr:
    return x + y

class C[AnyStr: (str, bytes)]:
    def __init__(self, x: AnyStr) -> None:
         self.x = x

type SpecificList[AnyStr: (str, bytes)] = list[AnyStr]
4 Likes
3

I’ve honestly never thought that AnyStr was a good name anyways; the typing docs list two separate things that the construct’s name could be confused for. Seeing as it’s been deprecated since 3.13, you might have a good opportunity to move away from it entirely:

def concat[T: (str, bytes)](x: T, y: T) -> T:
    return x + y
3 Likes