Simple commented example of a very simple hanoi backup rotation function, released MIT

hanoi-backups.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright © 2016 Taylor C. Richberger <taywee@gmx.com>
# This code is released under MIT license

import locale
import argparse
import string

def hanoi(day, tapes):
    # Make sure the recursion works on the proper schedule, with the bottom
    # tape only being written on the last day of the cycle
    day = day % (2 ** (tapes - 1))

    # An obvious algorithm takes direct advantage of the fact that the
    # frequency of the tape is correlated by its number, with tape 0 being
    # 2**1, tape 1 being 2**2, and so on.  This would make tape 0 be written
    # every day, but by reversing the test order, each tape's frequency is
    # reduced to half, because every other iteration is overridden by the next
    # tape up in the cycle.
    # If you are iterating days manually (rather than using the obvious days
    # since epoch method), this has the advantage that the longest-living tape
    # in the cycle is written first.
    for i in reversed(range(tapes)):
        if day % (2 ** i) == 0:
            return i

def main():
    locale.setlocale(locale.LC_ALL, '')
    parser = argparse.ArgumentParser(description='Do Something')
    parser.add_argument('-t', '--tapes', help='How many tapes', type=int, required=True)
    args = parser.parse_args()

    days = 2 ** (args.tapes - 1)
    width = len(str(days))

    for i in range(days):
        tape = hanoi(day=i, tapes=args.tapes)
        print('{day:0{width}d}:{spaces}{tape}'.format(day=i + 1, width=width, spaces=' ' * tape, tape=string.ascii_uppercase[tape]))

if __name__ == '__main__':
    main()