Append a section to the body.

        :param data: The data to append.
        :type data: str or bytes

def append(self, data):
        """Append a section to the body.

        :param data: The data to append.
        :type data: str or bytes
        """
        if isinstance(data, six.text_type):
            self._message.add_body_data(data.encode(self._encoding))
        elif isinstance(data, six.binary_type):
            self._message.add_body_data(data)