Before 3.10, I was using Union
to create union parameter annotations:
from typing import Union class Vector: def __mul__(self, other: Union["Vector", float]): pass
Now, when I use the new union shorthand syntax:
class Vector: def __mul__(self, other: "Vector" | float): pass
I get the error:
TypeError: unsupported operand type(s) for |: ‘str’ and ‘type’
Is this not supported?
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Answer
The fact that it’s being used as a type hint doesn’t really matter; fundamentally the expression "Vector" | float
is a type error because strings don’t support the |
operator, they don’t implement __or__
. To get this passing, you have three options:
Defer evaluation (see PEP 563):
from __future__ import annotations class Vector: def __mul__(self, other: Vector | float): ...
Make the whole type a string (effectively the same as deferring evaluation):
class Vector: def __mul__(self, other: "Vector | float"): ...
Keep using the
Union
:from typing import Union class Vector: def __mul__(self, other: Union["Vector", float]): ...
You can see further discussion, without a resolution as yet, on this bug.