Last time we saw how to extract the sequence from our GenBank file, but the final result might not be as nice as we wanted it to be. So, we need to make it prettier. Running last entry’s script we end up with this sequence

1 gtttggtcct aaccttgtaa tcaattttta cttaatatac acatgcaagt ctccgcaccc 61 ctgtgaaaac gcccttaaat cccccatggg ataaggagct ggtatcaggc acgaaaatct
121 gcccaaaaca cctagctatg ccacacccac aagggtactc agcagtgattgacattattt
181 ataagcgcca gcttgactca gttaaagtaa agagagccgg caaatctggt gccagccgcc
241 gcggttaccc cacgtggctc aaattgattt ctttcggcgt aaagcgtgat taaagtgccc
301 atcaacattg gagttaaact aaaattaagc tgtgacacgc ttattttaca gaaaagcaca
361 aacgaaagtt acttcaattt aaacaacttg aattcacgac agtcaggaca caaactggga
421 ttagataccc cactatgccc gaccgtaaac tttaatttac accatcaccg ccagagaact
481 acgagcaaag cttaaaactc aaaggacttg acggtccccc acatccccct agaggagcct
541 gtcctttaat cgataatccc cgcttaacct caccattctt agtctttcag cctgtatacc
601 tccgtcgtca gcttaccccg tgagcgaaaa ttagtgagct taatgtccac acgtctacac
661 gtcaggtcaa ggtgcagcaa atataatggg aagagatggg ctacactttc tagtctagaa
721 tatacgaaag accacctatg aaacctggtc agaaggcgga tttagaagta aaaggaaacc
781 agagcatccc ttttaatttg gcactggggc atgtacacac cgcccgtcac cctcttcaaa
841 gcctaatttt agtatctaac caactaacgc ctagtagaag aggcaagtcg taacatggta
901 agtataccgg aaggtgtgct tggaaacaaa atatagccta atcaaagcat ttcgcttaca
961 ccgaaaagtt atctgtgaaa ttcagattat tttgagctaa aaatctagcc ccactttatt
1021 ctataatccc ttatcactta aattcatgaa tcaaaacatt ttaataatca agtaaaggcg
1081 attgaaaaat taataggagc aatatatact gtaccgcaag ggaaagatga aatagaaatg
1141 aaataataat taaagcataa aaaagtaaag attaaatctt gtaccttttg catcatgatt
1201 taactagtct acccaggcaa aatgatttta agtctgacct cccgaaacta agtgagctac
1261 ttcaaggcag cttaatgagc aaatccgtct ctgtcgcaaa agagtggaga gaccttcaag
1321 tagaagtgat agacctaacg aacttagtaa tagctggtta ttcaagaaaa ggatctcagt
1381 ccaacctaaa gtcaaattaa tgtttaaaaa taaaaattct gaccttagag taattcaatt
1441 aaggtacagc ctacttgaaa caggatacaa ccttaactaa tgggtaactt accccttcat
1501 cttttaagtg ggcctaaaag cagccacctt taaaatagcg tcaaagctta gccgtcctat
1561 acatctaata ccaaaaacat ctatgaaccc tatactcata ttgaataatt ctatattatt
1621 atagagattt ttatgttaaa actagtaaca agaattaaat tttctctatt atgttcgtgt
1681 acatcagaaa ggataaacca ctgataattg acatgcatga gtaaaaagca gtaacttaac
1741 aagaaaaccc tcctaactct aatgttaacc taacacaagt acatctcaag aaagatttaa
1801 agaaaaagaa ggaactcggc aaacattaac ctcgcctgtt taccaaaaac atcgcctctt
1861 gtcaaaattt aagaggtcca gcctgcccag tgaccctgtt caacggccgc ggtatcctaa
1921 ccgtgcgaag gtagcgtaat cacttgttct ttaaataagg actagtatga atggcaccac
1981 gagggttata ctgtctcctt tttctaatca gtgaaactaa tcttcccgtg aagaagcggg
2041 aatttttata taagacgaga agaccctatg gagctttaga cgagtaacaa ctgctaattt
2101 tataatattt cagataatat ctctatccta gcattatgat tataagtctt tggttggggt
2161 gaccgcggag aaaaaaataa cctccacatt gaaagaatat tattctaagc aaaaagacac
2221 atctttaagc atcaacaaat tgacatctat tgacccaata ttttgatcaa cgaaccaagt
2281 taccctaggg ataacagcgc aatccacttc gagagctctt atcgacaagt gggcttacga
2341 cctcgatgtt ggatcagggt atcctagtgg tgtagccgct actaaaggtt cgtttgttca
2401 acgattaaaa ccct //

Notice that there were no mention to the // at the end of the file This double slash represents the EOF of a GenBank file. Ideally we need to remove it from the final output, as we need to remove the nucleotide number at the beginning of each line. In order to do that we need to modify our last script. First we will add a condition on the for loop that will take care of the double slash at the end. Then we need to use a trick to remove the numbers from the lines.

We should expect the numbers to be at the beginning of the line, and never in another place. The long way would be to create a regular expression and then replace every number occurrence with an empty string. But Python comes with batteries included, so we will take the short path. We use the lstrip string method that will remove characters from the left part of the string, and set it to remove numbers from 0 to 9 and the extra space before the nucleotides. And our script will like this:

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import sys

gbfile = open(sys.argv[1], 'r').readlines()

sequence = ''
issequence = False
for line in gbfile:
    if issequence == True and not line.find('/') == 0:
        sequence += line.lstrip('0123456789 ')
    elif line.find('ORIGIN') >= 0:
        issequence = True

print sequence

Notice that the first if condition was modified to include a condition that we do not find a slash. And at the line where we concatenate the sequence we added a lstrip('0123456789 ') to modify the string on the fly. The final result looks much better now. But we still have a small “problem”: there are spaces between groups of 10 nucleotides and we want to get rid of them. We would be surprised if it was difficult, and as expected it is not. We used here the replace method and we can use it here too. We only need to modify the line that concatenates the sequence, and our final script will be

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import sys

gbfile = open(sys.argv[1], 'r').readlines()

sequence = ''
issequence = False
for line in gbfile:
    if issequence == True and not line.find('/') == 0:
        sequence += line.lstrip('0123456789 ').replace(' ', '')
    elif line.find('ORIGIN') >= 0:
        issequence = True

print sequence

Notice that we add the replace method after the lstrip, but it can either way. The output should be only the nucleotides, with no space or numbers.