Use default hash method to return hash value of a piece of string
        default setting use 'utf-8' encoding.

        :type text: text_type
        :param text: a text object

def of_text(self, text, encoding="utf-8"):
        """
        Use default hash method to return hash value of a piece of string
        default setting use 'utf-8' encoding.

        :type text: text_type
        :param text: a text object
        """
        m = self.hash_algo()
        m.update(text.encode(encoding))
        return self.digest(m)