>>> self.get_qual_range("DLXYXXRXWYYTPMLUUQWTXTRSXSWMDMTRNDNSMJFJFFRMV")
        (68, 89)

def get_qual_range(self, phred_string):
        """
        >>> self.get_qual_range("DLXYXXRXWYYTPMLUUQWTXTRSXSWMDMTRNDNSMJFJFFRMV")
        (68, 89)
        """
        values = [ord(char) for char in phred_string]
        return min(values), max(values)