[issue29262] Provide a way to check for *real* typing.Union instances

[Ivan Levkivskyi]

Ivan Levkivskyi added the comment:

In principle, such a function could be added if it is not called ``isinstance``. For example, we could add a helper ``is_union(tp)`` (or maybe also ``is_generic(tp)`` etc). Such function(s) will be simple one-liners wrapping private API in a right way (e.g. using _gorg instead of __origin__ where needed etc).

Guido, what do you think?

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nosy: +gvanrossum, levkivskyi
type:  -> enhancement

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<http://bugs.python.org/issue29262>
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