Age, Workclass, Fnlwgt, Education, Educationnum, Maritalstatus, Occupation, Relationship, Race, Sex, Capitalgain, Capitalloss, Hoursperweek, Nativecountry, Class f = open('t', 'w') for line in open('train.csv'): line = line[:-1].split(',') if len(line) < 1: continue if line[0] == '?': line = ','.join(line) print line age = int(line[0]) if age in range(25): age = '0025' if age in range(25, 40): age = '2639' if age in range(40, 60): age = '4059' if age in range(60, 80): age = '6080' if age in range(80, 120): age = '8080' line[0] = age line = ','.join(line) f.write(line+'\n')