私の Python Caesar Cipher では、最後にシフトされた文字のみが表示されるのはなぜですか?

<code class="python">plainText = raw_input("What is your plaintext? ")
shift = int(raw_input("What is your shift? "))

def caesar(plainText, shift):
    cipherText = ""
    for ch in plainText:
        if ch.isalpha():
            stayInAlphabet = ord(ch) + shift
            if stayInAlphabet > ord('z'):
                stayInAlphabet -= 26
            finalLetter = chr(stayInAlphabet)
        cipherText += finalLetter
    print "Your ciphertext is: ", cipherText
    return cipherText

caesar(plainText, shift)</code>

<code class="python">def caesar(plaintext, shift):
    alphabet = string.ascii_lowercase
    shifted_alphabet = alphabet[shift:] + alphabet[:shift]
    table = string.maketrans(alphabet, shifted_alphabet)
    return plaintext.translate(table)</code>