def main(argv=None):
    """script main.

    parses command line options in sys.argv, unless *argv* is given.
    """

    if not argv:
        argv = sys.argv

    # setup command line parser
    parser = optparse.OptionParser(version="%prog version: $Id: contigs2random_sample.py 2871 2010-03-03 10:20:44Z nicki $",
                                   usage=globals()["__doc__"])

    parser.add_option("-m", "--species-map", dest="species_map", type="string",
                      help="text file specifying the mapping between contig and genome")

    parser.add_option("-g", "--genome-dir", dest="genome_dir", type="string",
                      help="specify directory where genome / genomes are stored")

    # add common options (-h/--help, ...) and parse command line
    (options, args) = E.Start(parser, argv=argv)

    # read in contig lengths into dictionary
    E.info("reading contigs file")
    c_contigs = 0
    contigs_lengths = {}
    for fasta in FastaIterator.iterate(options.stdin):
        c_contigs += 1

        # titles of fasta records must be single strings with no special
        # characters
        contigs_lengths[fasta.title.split(" ")[0]] = len(fasta.sequence)

    E.info("read %i contigs" % c_contigs)

    # read in mapping between spcies and contigs
    species_map = {}
    for line in open(options.species_map).readlines():
        data = line[:-1].split("\t")
        contig, species = data[0], data[1]
        species_map[contig] = species

    # read genomes into memory
    # NB this may need optimisin if using large
    # genomes or many genomes
    E.info("reading genomes from %s" % options.genome_dir)

    # The directory must ONLY contain genome files!!
    genomes_sequences = {}
    c_genomes = 0
    for genome_file in glob.glob(os.path.join(options.genome_dir, "*")):
        c_genomes += 1
        for fasta in FastaIterator.iterate(IOTools.openFile(genome_file)):
            genomes_sequences[fasta.title] = fasta.sequence
    E.info("read %i genomes from %s" % (c_genomes, options.genome_dir))

    # iterate over the contigs and sample from the respective genome
    E.info("iterating over contigs")
    c_contigs_output = 0
    for contig, length in contigs_lengths.iteritems():
        if contig not in species_map:
            E.warn("contig %s not in species map file" % contig)
        else:
            c_contigs_output += 1
            genome = species_map[contig]
            genome_length = len(genomes_sequences[genome])

            # get the start position from which to sample
            start = random.randint(1, genome_length)
            try:
                end = start + length - 1
            except __HOLE__:
                print "end of sampled contig extends beyond length of genome"

            sampled_seq = genomes_sequences[genome][start:end]
            options.stdout.write(
                ">%s_random\n%s\n" % (contig + "_%s" % species_map[contig], sampled_seq))

    E.info("written %i contigs" % c_contigs_output)
    # write footer and output benchmark information.
    E.Stop()
dataset/ETHPy150Open CGATOxford/cgat/scripts/contigs2random_sample.py/main