[Python] typing.Union allows for callables as its type arguments

I am concerned about why callables are valid type arguments to pass to Union[] (as well as some other typing._GenericAlias objects)? What is the intended purpose of this?

>>> def foo(): pass
...
>>> Union[foo, print]
typing.Union[foo, <built-in function print>]


After some further investigation I found that, for some reason, the code in Python 3.7.0 stdlib does not match one located in typing GitHub repository. But typing module that my current Python installation uses allows callables explicitly:

def _type_check(arg, msg, is_argument=True):
<...>
if not callable(arg):
raise TypeError(f"{msg} Got {arg!r:.100}.")
return arg

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