'Reverse look-up.
:param list lst: The list to look up in.
:param item: The item to look for.
:return: Offset of the item if found. A ValueError is raised if the item is not in the list.
:rtype: int'

@staticmethod
def _rfind(lst, item):

    try:
        return dropwhile((lambda x: (lst[x] != item)), reversed(xrange(len(lst)))).next()
    except Exception:
        raise ValueError(('%s    not    in    the    list' % item))
