I think we type this with Label elsewhere?

@jreback I did a grep and only saw Any

Label is for index values, this is an array, so Any is correct I think

Label was an alias for Union[Hashable, None] to workaround a mypy bug that has since been fixed. Now mypy recognizes None as being Hashable.

wrt Any

from https://github.com/python/typeshed/blob/master/CONTRIBUTING.md#incomplete-stubs

Included functions and methods must list all arguments, but the arguments can be left unannotated. Do not use Any to mark unannotated arguments or return values.

from https://github.com/python/typeshed/blob/master/CONTRIBUTING.md#conventions

When adding type hints, avoid using the Any type when possible. Reserve the use of Any for when:

the correct type cannot be expressed in the current type system; and
to avoid Union returns (see above).

Note that Any is not the correct type to use if you want to indicate that some function can accept literally anything: in those cases use object instead.

Based on that explanation, it should be object here

I've used object, but had to do a type ignore when any() was called on a comparison. I couldn't figure out how to work around that. See latest commit.