Subtracts database 2 from database 1. Results can then be dumped to view what kmers are present only in database 1.
    :param database_1: First database generated by kmc.
    :param database_2: Second database generated by kmc.
    :param results: Result database, containing reads in both database 1 but not in 2..
    :param exclude_below: Don't subtract kmers from database 1 that have less than this many occurrences
    in database 2.
    :param returncmd: If true, will return the command used to call KMC as well as out and err.
    :return: Stdout and stderr from kmc.

def subtract(database_1, database_2, results, exclude_below=1, returncmd=False):
    """
    Subtracts database 2 from database 1. Results can then be dumped to view what kmers are present only in database 1.
    :param database_1: First database generated by kmc.
    :param database_2: Second database generated by kmc.
    :param results: Result database, containing reads in both database 1 but not in 2..
    :param exclude_below: Don't subtract kmers from database 1 that have less than this many occurrences
    in database 2.
    :param returncmd: If true, will return the command used to call KMC as well as out and err.
    :return: Stdout and stderr from kmc.
    """
    cmd = 'kmc_tools kmers_subtract {} {} -ci{} {}'.format(database_1, database_2, str(exclude_below), results)
    out, err = accessoryfunctions.run_subprocess(cmd)
    if returncmd:
        return out, err, cmd
    else:
        return out, err