Author: Mohit Radadiya This function generates the key in a cyclic manner until it's length isn't equal to the length of original text  generatekeyTHE GERMAN ATTACK,SECRET 'SECRETSECRETSECRE' This function returns the encrypted text generated with the help of the key  ciphertextTHE GERMAN ATTACK,SECRETSECRETSECRE 'BDC PAYUWL JPAIYI' This function decrypts the encrypted text and returns the original text  originaltextBDC PAYUWL JPAIYI,SECRETSECRETSECRE 'THE GERMAN ATTACK'
from string import ascii_uppercase

dict1 = {char: i for i, char in enumerate(ascii_uppercase)}
dict2 = dict(enumerate(ascii_uppercase))


# This function generates the key in
# a cyclic manner until it's length isn't
# equal to the length of original text
def generate_key(message: str, key: str) -> str:
    """
    >>> generate_key("THE GERMAN ATTACK","SECRET")
    'SECRETSECRETSECRE'
    """
    x = len(message)
    i = 0
    while True:
        if x == i:
            i = 0
        if len(key) == len(message):
            break
        key += key[i]
        i += 1
    return key


# This function returns the encrypted text
# generated with the help of the key
def cipher_text(message: str, key_new: str) -> str:
    """
    >>> cipher_text("THE GERMAN ATTACK","SECRETSECRETSECRE")
    'BDC PAYUWL JPAIYI'
    """
    cipher_text = ""
    i = 0
    for letter in message:
        if letter == " ":
            cipher_text += " "
        else:
            x = (dict1[letter] - dict1[key_new[i]]) % 26
            i += 1
            cipher_text += dict2[x]
    return cipher_text


# This function decrypts the encrypted text
# and returns the original text
def original_text(cipher_text: str, key_new: str) -> str:
    """
    >>> original_text("BDC PAYUWL JPAIYI","SECRETSECRETSECRE")
    'THE GERMAN ATTACK'
    """
    or_txt = ""
    i = 0
    for letter in cipher_text:
        if letter == " ":
            or_txt += " "
        else:
            x = (dict1[letter] + dict1[key_new[i]] + 26) % 26
            i += 1
            or_txt += dict2[x]
    return or_txt


def main() -> None:
    message = "THE GERMAN ATTACK"
    key = "SECRET"
    key_new = generate_key(message, key)
    s = cipher_text(message, key_new)
    print(f"Encrypted Text = {s}")
    print(f"Original Text = {original_text(s, key_new)}")


if __name__ == "__main__":
    import doctest

    doctest.testmod()
    main()
