How do I create user-defined warnings?

[Clay Hobbs]

I already know how to make user-defined exceptions, like this one:

	class MyException(Exception):
	    pass

But for a module I'm making, I would like to make a warning (so it just
prints the warning to stderr and doesn't crash the program).  I have
tried this:

	class MyWarning(Warning):
	    pass

And it behaves like a normal error.  Please help me, I can't figure out
what I'm doing wrong.

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