file = '/Users/svetlana/Downloads/E.coli.sequence.txt'

window = 100000

step = 1000

sequence =

with open(file, 'r') as fasta:

• fasta.readline() for line in fasta:

  • if line[0] != '>':

    • sequence += line.strip()

sumGCscew = 0 with open('out.txt', 'w') as out:

• for i in range(0, len(sequence), step):
  • positionseq = sequence[i:i+window]

    if len(positionseq) < window:

    • break
    Ccnt = 0 Gcnt = 0 for nucl in positionseq:
    • if nucl == 'C':
      • Ccnt += 1
      elif nucl == 'G':
      • Gcnt += 1
    if Ccnt == 0 and Gcnt == 0:
    • GCscew = 0
    else:
    • GCscew = (Gcnt - Ccnt)/(Gcnt + Ccnt)
    sumGCscew += GCscew print(f'{i}\t{GCscew:.3f}\t{sumGCscew:.3f}', file=out)