def _get_start(loc):
    """Get the starting location position of a feature in the contig (accounting for the strand)"""
    if loc.strand == '+':
        return loc.start
    if loc.strand == '-':
        st = loc.start - (loc.length - 1)
        if st < 0:
            raise ValueError(f'{loc} is not a valid location on this assembly')
        return st
    return 0