Write out a file containing only the list of OTU IDs from the kraken data.
    One line per ID.

    :type otu_ids: list or iterable
    :param otu_ids: The OTU identifiers that will be written to file.
    :type fp: str
    :param fp: The path to the output file.

def write_otu_file(otu_ids, fp):
    """
    Write out a file containing only the list of OTU IDs from the kraken data.
    One line per ID.

    :type otu_ids: list or iterable
    :param otu_ids: The OTU identifiers that will be written to file.
    :type fp: str
    :param fp: The path to the output file.
    """
    fpdir = osp.split(fp)[0]

    if not fpdir == "" and not osp.isdir(fpdir):
        raise RuntimeError("Specified path does not exist: {}".format(fpdir))

    with open(fp, 'wt') as outf:
        outf.write('\n'.join(otu_ids))