Added Optional annotation for first parameter of object.isinstance

[erictraut]

Added Optional annotation for first parameter of object.isinstance because it's able to accept None as a value.

[srittau]

This is a no-op, since None is a valid instance of object. Type checkers should already accept isinstance(None, ...). Do you have an example where this leads to problems?

[erictraut]

Why would None be a valid instance of object? Is this documented? I don't see where in the specs (pep 484 or elsewhere) where this is documented.

If None is a valid instance of object, is it possible to specify that a parameter must be an object but not None?

[srittau]

None being an instance of object is just the result of Python's type system, where object is at the root of the type hierarchy:

>>> isinstance(None, object)
True
>>> type(None)
<class 'NoneType'>
>>> type(None).__bases__
(<class 'object'>,)

I don't think it's currently possible to allow any value except None. Cf. python/typing#614

[erictraut]

Thanks for the explanation. I was under the impression that None was a specialized type not derived from object. Closing the PR.