Caesar Cipher Python [Encrypt / Decrypt]

caesar.py

############ Made By Mouad KHIAT / Python 3.7
############ if you have another idea to write this famous cipher put it in the comment
############ It's started with DOHD MDFWD HVW ==> ALEA JACTA EST (key = 3)
def transform(x): 
    x = list(x)
    for i,n in enumerate(x):
        if n in ABC:
            x[i] = ABC.index(n)
    return x
def crypt(x,key):
    x = transform(x)
    x = [(n + key)%26 if type(n) == int else n for i,n in enumerate(x)]
    return x

def decrypt(x,key):
    x = transform(x)
    d = []
    if key == None:
        for k in range(26):
            d.append(crypt(x,-k))
        x = d
        return x
    else: 
        return crypt(x,-key)

def caesar(x,key,mod):
    v = []
    if mod:
        x = crypt(x,key)
    else:
        x = decrypt(x,key)
    for i,n in enumerate(x):
        if type(n) == int:
            x[i] = ABC[n]
        elif type(n) == list:
            for j,m in enumerate(n):
                if type(m) == int:
                    n[j] = ABC[m]
            value = ''.join(n)
            #v.append('==> key = {} : {}'.format(i,value)) #for old version
            v.append(f'==> key = {i} : {value}')
    if len(v) != 0:
        return '\n'.join(v)
    #return "==> {}.format(''.join(x))" #for old version
    return f"==> {''.join(x)}"

ABC = list('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
if input('==> Encrypt or Decrypt ? : ').lower() == 'encrypt':
    x = input('Enter what you want to encrypt => ').upper()
    key = int(input('Enter the key  [0-25] => '))
    mod = True
else : 
    x = input('Enter what you want to decrypt => ').upper()
    if input('Do you have the key ? (y/n) :').lower() == 'y':
        key = int(input('Enter the key => '))
    else: key=None
    mod = False	
print(caesar(x,key,mod))

ascii_letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ-."

def encrypt(text: str, key: int) -> str:
return "".join(ascii_letters[(ascii_letters.index(plain_letter) + key) % len(ascii_letters)] for plain_letter in text)

def decrypt(encrypted_text: str, key: int) -> str:
return "".join(ascii_letters[(ascii_letters.index(plain_letter) - key) % len(ascii_letters)] for plain_letter in encrypted_text)