Code to 'slice' or subset genbank format sequences from one gene specifier to another by looking up their locations.

slice_genes.py

#!/usr/bin/env python

# Slice subregions out of a genbank between 2 genes.
# Usage:
#   slice_genes.py infile.gbk gene1:gene2:strand

from Bio import SeqIO
import sys, argparse

def get_args():
    """Parse command line arguments"""

    try:
        parser = argparse.ArgumentParser(
            description='Subset genbanks between 2 genes.')
        parser.add_argument('-i', '--infile', action='store',
                            help='Input genbank file to slice.')
        parser.add_argument('-r', '--range', action='store',
                            help='The 2 gene LOCUS TAGS to slice between')
        if len(sys.argv) == 1:
            parser.print_help(sys.stderr)
            exit(1)
    except:
        sys.stderr.write("An exception occurred with argument parsing. Check your provided options.")

    return parser.parse_args()


def main():
    args = get_args()
    genes = args.range.split(':')
    sys.stderr.write('Fetching subsequence betweeen {} and {}.\n'.format(genes[0], genes[1]))

    records = SeqIO.parse(args.infile, 'genbank')

    for record in records:
        sys.stderr.write('Operating on {}.\n'.format(record.id))
        loci = [feat for feat in record.features if feat.type == "CDS"]
        try:
            start = min([int(l.location.start) for l in loci if l.qualifiers['locus_tag'][0] in genes])
            end = max([int(l.location.end) for l in loci if l.qualifiers['locus_tag'][0] in genes])
        except ValueError:
            sys.stderr.write('No indices returned for those loci, assume they don\'t feature in this record, moving on...\n.')
            continue
        try:
            (start and end)
            subrecord = record[start:end]
            print subrecord.format('genbank')
        except NameError:
            sys.stderr.write('Didn\'t get any indices even though the genes seemed to match. Couldn\'t slice.\n')
            pass

if __name__ == '__main__':
    main()