Ceasar Cipher challenge

def encrypter(text, key):
    alph = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ., '
    ciphered_text = ''
    for i in range(len(text)):
        t_numeric_val = alph.index(text[i])
        k_numeric_val = alph.index(key[i])
        c_numeric_val = (t_numeric_val + k_numeric_val) % 29
        ciphered_text += alph[c_numeric_val]
##        print(text[i],t_numeric_val,key[i], k_numeric_val, ciphered_text)

    return ciphered_text


print(encrypter("ONE IF BY LAND, TWO IF BY SEA.", "THE CELERY STALKS AT MIDNIGHT."))
## EUI,KJKFMXKSDDJJIVOSHRHEIHYLTX
##def decrypter(text):
##    for i