atbash.py

def atbash_encrypt(input_string):
    alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    reverse_alpha = 'ZYXWVUTSRQPONMLKJIHGFEDCBA'

    atbash_string = ''

    for char in input_string:
        char = char.upper()
        if char in alpha:
            position = alpha.find(char)
            atbash_string += reverse_alpha[position]
        else:
            atbash_string = None
            break
        
    return atbash_string


def atbash_decrypt(atbash_string): 
    
    ALPHA='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    REVERSEALPHA='ZYXWVUTSRQPONMLKJIHGFEDCBA'
    
    atbash_string=atbash_string.upper()
   
    decrypted_string=''
    
    for l in atbash_string:
        if l in REVERSEALPHA:
            letterindex = REVERSEALPHA.find(l)
            decrypted_string = decrypted_string + ALPHA[letterindex]
        else: 
            decrypted_string=decrypted_string + l
            
    return decrypted_string


def atbash_wrapper(input_string, method='encrypt'):
    
    if method == 'encrypt':
        output_string = atbash_encrypt(input_string)
    elif method == 'decrypt':
        output_string = atbash_decrypt(input_string)
    else:
        output_string = "method should be either 'decrypt' or 'encrypt'"
    
    return output_string