I'm glad you caught that!  First things first: the converted code should behave identically to the existing code, including raising the same exceptions.


If you examine the exception hierarchy:
    http://docs.python.org/3.4/library/exceptions.html#exception-hierarchy

you'll see that "OverflowError" is a subclass of "ArithmeticError".  In other words, it represents when you perform an arithmetic operation that overflows the result type.  Using it to also represent "you specified a value that is out of range for this conversion" seems wrong.

So I like #3 as well.

Could _PyLong_UnsignedInt_Converter catch the OverflowError raised by PyLong_AsUnsignedLong and reraise it as ValueError?