derotn.py

#!/usr/bin/python
import string

# Given startString, this loops through rot(n) until it is un-rotted back to original

# rot_alpha courtesy of http://eddmann.com/posts/implementing-rot13-and-rot-n-caesar-ciphers-in-python/
def rot_alpha(n):
    from string import ascii_lowercase as lc, ascii_uppercase as uc
    lookup = string.maketrans(lc + uc, lc[n:] + lc[:n] + uc[n:] + uc[:n])
    return lambda s: s.translate(lookup)


startString = "This is my string"
rot = 14

transString = rot_alpha(rot)(startString)
checkString = ""
run = 1
while checkString != startString:
	print("(Translation round: %02i) Start: %s | Trans: | %s" % (run, startString, transString))
	checkString = transString
	transString = rot_alpha(rot)(transString)
	run += 1