import sys filename, Rv, Ra = sys.argv[1:] Rv = float(Rv) Ra = float(Ra) for line in open(filename): if line.startswith('#'): continue u, i = map(float, line.split()) if Ra != 0: u = u - i * Ra * 0.001 if Rv != 0: i = i - u / Rv * 1000. print u, i