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

[Evan]

Evan added the comment:

I'm also interested in this. I've been using 'thing.__origin__ is typing.Union', but this doesn't work in some of the older versions of typing.

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nosy: +evan_

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29262>
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