Given coordinates in 0-based interbase coordinates, return a Locus
        instance.

def from_interbase_coordinates(contig, start, end=None):
        '''
        Given coordinates in 0-based interbase coordinates, return a Locus
        instance.
        '''
        typechecks.require_string(contig)
        typechecks.require_integer(start)
        if end is None:
            end = start + 1
        typechecks.require_integer(end)
        contig = pyensembl.locus.normalize_chromosome(contig)
        return Locus(contig, start, end)