@sender.setter<EOL><INDENT>def sender(self, value):<DEDENT>
if isinstance(value, Recipient):<EOL><INDENT>if value._parent is None:<EOL><INDENT>value._parent = self<EOL>value._field = '<STR_LIT>'<EOL><DEDENT>self.__sender = value<EOL><DEDENT>elif isinstance(value, str):<EOL><INDENT>self.__sender.address = value<EOL>self.__sender.name = '<STR_LIT>'<EOL><DEDENT>else:<EOL><INDENT>raise ValueError(<EOL>'<STR_LIT>')<EOL><DEDENT>self._track_changes.add('<STR_LIT>')<EOL>
sender is a property to force to be always a Recipient class