[Python] How to specify the values of an union in a type hint?

I would like to know how to point out the possible values of an union argument. Let's use the parameter axis from pandas (pandas.DataFrame.dropna) for this example.

The type hint should be something like this:

axis: Union[int, str] = 0

Now, how do we communicate to the users the possible values pairs of values for that parameter? Is it better to define it in the docstring?

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