@staticmethod
def letter_mutation(string):
    """
        Coderbyte challenge: Letter Changes
        :param string: a sentence
        :return: str, transformed sentence
        """
    alphabet = list(range(97, 123))
    alphabet_len = len(alphabet) - 1
    ret = ''
    vowels = list('aeiou')
    for x in list(string):
        r = x
        if ord(x) in alphabet:
            if ord(x) == alphabet[alphabet_len]:
                r = chr(alphabet[0])
            else:
                r = chr(ord(x) + 1)
        if r in vowels:
            r = r.upper()
        ret += r
    return ret
