Function decrypt

ciphers/autokey.py:77–134

Decrypt a given `ciphertext` (string) and `key` (string), returning the decrypted ciphertext. >>> decrypt("jsqqs avvwo", "coffee") 'hello world' >>> decrypt("vvjfpk wj ohvp su ddylsv", "TheAlgorithms") 'coffee is good as python' >>> decrypt("vvjfpk wj ohvp su ddylsv", "

(ciphertext: str, key: str)

def decrypt(ciphertext: str, key: str) -> str:
    """
    Decrypt a given `ciphertext` (string) and `key` (string), returning the decrypted
    ciphertext.

    >>> decrypt("jsqqs avvwo", "coffee")
    'hello world'
    >>> decrypt("vvjfpk wj ohvp su ddylsv", "TheAlgorithms")
    'coffee is good as python'
    >>> decrypt("vvjfpk wj ohvp su ddylsv", "")
    Traceback (most recent call last):
        ...
    ValueError: key is empty
    >>> decrypt(527.26, "TheAlgorithms")
    Traceback (most recent call last):
        ...
    TypeError: ciphertext must be a string
    >>> decrypt("", "TheAlgorithms")
    Traceback (most recent call last):
        ...
    ValueError: ciphertext is empty
    >>> decrypt("vvjfpk wj ohvp su ddylsv", 2)
    Traceback (most recent call last):
        ...
    TypeError: key must be a string
    """
    if not isinstance(ciphertext, str):
        raise TypeError("ciphertext must be a string")
    if not isinstance(key, str):
        raise TypeError("key must be a string")

    if not ciphertext:
        raise ValueError("ciphertext is empty")
    if not key:
        raise ValueError("key is empty")

    key = key.lower()
    ciphertext_iterator = 0
    key_iterator = 0
    plaintext = ""
    while ciphertext_iterator < len(ciphertext):
        if (
            ord(ciphertext[ciphertext_iterator]) < 97
            or ord(ciphertext[ciphertext_iterator]) > 122
        ):
            plaintext += ciphertext[ciphertext_iterator]
        else:
            plaintext += chr(
                (ord(ciphertext[ciphertext_iterator]) - ord(key[key_iterator])) % 26
                + 97
            )
            key += chr(
                (ord(ciphertext[ciphertext_iterator]) - ord(key[key_iterator])) % 26
                + 97
            )
            key_iterator += 1
        ciphertext_iterator += 1
    return plaintext