[Python] Create a typing from a custom dataclass

I'm currently working with a dataclass (defined in one of the dependencies I'm currently working with inside of my project), which is defined similar to this snippet:

from dataclasses import dataclass
from typing import Union

class X:
...

class Y:
...

@dataclass
class Container:
data: Union[X, Y, dict]


Then, within my project, I wanted to specify some cases where I already know the type of data. With Container being a dataclass, I know it is not possible to hint directly over the attribute as following:

my_container = Container(X())
my_container.data: X # IDE complains


I was wondering if it is possible then to specify it anyhow similar to Container[X] to define that the only attribute it is from the type I already know of.

If not, is there any dunder method to add at the dataclass to allow this typing?

Note: I am not allowed to modify the original Container code.

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