Кто может помочь с Python?

filename = 'file.txt'

while True:
    i = 0
    try:
        with open(filename, 'r') as f:
            l = f.readline()
            i = int(l)
    except:
        pass
    else:
        i += 1

    if i == 9999:
        break

    with open(filename, 'w') as f:
        f.write("{:04d}".format(i))