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Is your feature request related to a problem? Please describe.

This is similar to #161. I have a class that wraps some YAML being loaded and want to make sure I get strings as opposed to floats for values such as 1.1. My users forget to quote them all the time.

    @typechecked
    class Component:
        val: str

        def __init__(self, data):
            self.val = data["val"]

Describe the solution you'd like
Would like the above to raise an error when val=1.1 and pass when val='1.1'.

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Actually the solution in #161 works.