Find the index of `item` in the OrderedSet

        Example:
            >>> # ENABLE_DOCTEST
            >>> import utool as ut
            >>> self = ut.oset([1, 2, 3])
            >>> assert self.index(1) == 0
            >>> assert self.index(2) == 1
            >>> assert self.index(3) == 2
            >>> ut.assert_raises(ValueError, self.index, 4)

def index(self, item):
        """
        Find the index of `item` in the OrderedSet

        Example:
            >>> # ENABLE_DOCTEST
            >>> import utool as ut
            >>> self = ut.oset([1, 2, 3])
            >>> assert self.index(1) == 0
            >>> assert self.index(2) == 1
            >>> assert self.index(3) == 2
            >>> ut.assert_raises(ValueError, self.index, 4)
        """
        for count, other in enumerate(self):
            if item == other:
                return count
        raise ValueError('%r is not in OrderedSet' % (item,))