Example of Caesar and Vernam cipher encoders and decoders

cipher.py

import math


def encode(string, rot):
    phrase = string.lower().replace(" ", "")
    out = ""
    a = "abcdefghijklmnopqrstuvwxyz"
    for char in phrase:
        out += a[(a.index(char)+rot) % 26]
    return out


def decode(string):
    d = {"a":8.167, "b":1.492, "c":2.782, "d":4.253, "e":12.70, "f":2.228, "g":2.015, "h":6.094, "i":6.966, "j":0.153, "k":0.772, "l":4.025, "m":2.406, "n":6.749, "o":7.507, "p":1.929, "q":0.095, "r":5.987, "s":6.327, "t":9.056, "u":2.758, "v":0.978, "w":2.360, "x":0.150, "y":1.974, "z":0.074}
    a = "abcdefghijklmnopqrstuvwxyz"
    entropies = []
    for i in range(1, 27):
        total = 0
        out = ""
        for char in string:
            out += a[(a.index(char)+i) % 26]
        for char in out:
            total += - math.log(d[char]) / math.log(2)
        entropies.append([total, i])
    lowest = [0,0]
    for x in entropies:
        if x[0] < lowest[0]:
            lowest = x
    lowest.append(encode(string, - lowest[1]))
    return lowest

def vernam(string, key):
    key = key[:len(string)]
    x=""
    for char, pos in zip(string, key):
        x+= chr(ord(char) ^ ord(pos))
    return x

encoded = encode(raw_input("Caesar Cyper text >>> "), int(raw_input("ROT >>> ")))
print "Encoded:", encoded
decoded = decode(encoded)
print "Decoded:", decoded[2],"\nROT:", decoded[1],"\nEntropy:", decoded[0]

key = raw_input("Vernam key >>> ")
encoded = vernam(raw_input("Message >>> "), key)
print "Encoded:", encoded
decoded = vernam(encoded, key)
print "Decoded:", decoded