cesar.py

alphabet = []
for i in range (0,26):
    alphabet.append(chr(ord('A')+i))
for i in range (0,26):
    alphabet.append(chr(ord('a')+i))
for i in range (0,10):
    alphabet.append(chr(ord('0')+i))
alphabet.append(' ')
alphabet.append('!')

noCar = '?'

def modulo(num,mod):
    if num > 0:
        while num > mod-1:
            num -= mod
        return num
    else:
        while num < 0:
            num += mod
        return num

def AsciiToAlphabet(letter):
        for i in range (0,len(alphabet)):
            if(alphabet[i] == letter):
                return i
        return -1

def AlphabetToAscii(num):
        if(num >= len(alphabet)):
            return noCar
        else:
            return alphabet[num]

def Crypt(phrase,passphrase):
    rep = ""
    for i in range (0,len(phrase)):
        rep += AlphabetToAscii(modulo(AsciiToAlphabet(phrase[i]) + AsciiToAlphabet(passphrase[modulo(i,len(passphrase))]),len(alphabet)))
    return rep

def Uncrypt(phrase,passphrase):
    rep = ""
    for i in range (0,len(phrase)):
        rep += AlphabetToAscii(modulo(AsciiToAlphabet(phrase[i]) - AsciiToAlphabet(passphrase[modulo(i,len(passphrase))]),len(alphabet)))
    return rep

isContinue = True
while isContinue:
    mode = input("Quel mode (d/c/q) : ")
    while mode != "d" and mode != "c" and mode != "q":
        mode = input("Entrer (d/c/q)!\nQuel mode (d/c/q) : ")
    if mode == "q":
        isContinue = False
        continue
    word = input("Entrer mot : ")
    passphrase = input("Entrer passphrase : ")

    if mode == "c":
        print(Crypt(word,passphrase))
    else:
        print(Uncrypt(word,passphrase))