code: def parent_folder(self):
          # type: () -> Folder
          
          if self.__parent_folder is None:
              self.__parent_folder = self.account.get_folder_by_id(self.__parent_folder_id)
  
          return self.__parent_folder
docs: Returns the :class:`Folder <pyOutlook.core.folder.Folder>` this message is in
  
              >>> account = OutlookAccount('')
              >>> message = account.get_messages()[0]
              >>> message.parent_folder
              Inbox
              >>> message.parent_folder.unread_count
              19
  
          Returns: :class:`Folder <pyOutlook.core.folder.Folder>`