[Python] Python Typing: Put Constraint on Annotated

I would like to do some meta-programming with python type annotations.

I want to define a certain type of Annotated, constraining the type for the metadata of the Annotated special form.

For example, I want to write a function, which only allows for Annotated types whose first metadata entry is a tuple:

from typing import Annotated

PositiveIntWithExamples = Annotated[int, (12, 1001)]
Bad = Annotated[int, "This is bad."]

def extract_examples(annotated_type: "AnnotatedWithExamples") -> tuple:
return annotated_type.__metadata__[0]

extract_examples(PositiveInt)
extract_examples(Bad) # typechecker should alert here


In the example above, how would I have to define AnnotatedWithExamples?

I think it might be possible to achieve this with a mypy plugin, and bake the structure of AnnotatedWithExamples into the plugin. But is it possible to do this within the python typing system?

I don't think I can do this either with Annotated, or something equivalent with NewType, or can I?

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