Simple Python Caesar cipher decrypting/encrypting library

pyCaesar

# Just a simple Caesar cipher library

# Define a list of the alphabet
alphabet = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]
def decryptCharacter(char, rotation):
    # Find where in the alphabet our letter is (for example A would be index 0)
    indexOriginal = alphabet.index(char)
    # Now we take the index of the original letter and add our key, and this will be the index of the new letter
    indexNew = indexOriginal - rotation
    # This is just in case we're dealing with Z or something else where the index would go over 25. It makes the list basically loop infinitely
    if (indexNew > 25):
        indexNew = indexNew - 26
    # Now that we've done all that, we return the element from the alphabet list that's at our new index we just found
    return alphabet[indexNew]

def decryptString(string, rotation):
    output = ""
    for letter in string:
        # Ignore spaces
        if (letter == " "):
            output = output + " "
        # Call the decryptCharacter function for this letter and add the decrypted letter to the end of our output string
        else:
            output = output + decryptCharacter(letter, rotation)
    # We're done, return the output string we just put together
    return output

def encryptString(string, rotation):
    output = ""
    for letter in string:
        if (letter == " "):
            output = output + " "
        else:
            output = output + encryptCharacter(letter, rotation)
    return output

def encryptCharacter(char, rotation):
    indexOriginal = alphabet.index(char)
    indexNew = indexOriginal + rotation
    if (indexNew > 25):
        indexNew = indexNew - 26
    return alphabet[indexNew]