Returns the size of the :attr:`data` object in bytes (read-only).

def data_size(self):
        """ Returns the size of the :attr:`data` object in bytes (read-only)."""
        # Container
        if is_container(self._data):
            byte_length, bit_length = self._data.container_size()
            return byte_length + math.ceil(bit_length / 8)
        # Field
        elif is_field(self._data):
            return math.ceil(self._data.bit_size / 8)
        else:
            return 0