cypher.py

abc = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]

def move(texto, steps):
	if steps > 0:
		steps = steps - 26
	novo = ''
	for letra in texto.upper():
		if letra in abc:
			pos = abc.index(letra) + steps
			if pos > len(abc):
				pos = pos - len(abc)
			novo += abc[pos]
		else:
			novo += letra
	return novo

def clean(texto):
	ok = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','r','s','t','u','v','w','x','y','z',' ']
	novo = ''
	for letra in texto:
		if letra in ok:
			novo += letra
	return novo

def freq(texto, steps=None):
	if steps:
		texto = move(texto, steps)

	frequencia = {}
	for letra in clean(texto.lower()):
		if frequencia.has_key(letra):
			frequencia[letra]['total'] += 1
		else:
			frequencia[letra] = { 'total' : 1 }

	for f in frequencia:
		frequencia[f]['freq'] = frequencia[f]['total'] / (len(texto)*1.0)

	return frequencia

def sort(a):
	return sorted(a, key=lambda x: a[x]['freq'], reverse=True)

def calc_steps(c,d):
	return abc.index(c.upper()) - abc.index(d.upper())

def decypher(code, decode):
	if code[-4:] == '.txt':
		code = open(code, 'r').read()
	if decode[-4:] == '.txt':
		decode = open(decode, 'r').read()

	c = sort(freq(code))
	d = sort(freq(decode))
	print code
	for x in range(1,6):
		steps = calc_steps(c[x], d[x])
		print steps
		print move(code, steps)