python - GUI - How to save changes to file automatically? -

i´ve created 2 python files - first 1 stores main classes , second 1 gui uses functions first one. have file - list of items work - automatically save changes everytime add or delete item in gui window. i´ve got problem how write down 2 functions gui - "add_item" , "delete_item". add_item able add_item when gui window open, however, temporary, cos doesn´t save changes file (list of items). i´m beginner in python, many help.

here part of first py-file (that stores classes):

    def additem(self, item):         if isinstance(item, item):             if item not in self:                 self.append(item)             else:                 raise valueerror("item in class already")         else:             raise valueerror("object class item expected")      def additemwithname(self, name, size, price):         newitem = item(name, size, price)         self.add_item(newitem)      def deleteitem(self, item):         if isinstance(item, item):             if item in self:                 self.remove(item)             else:                 raise valueerror("item not deleted")         else:             raise valueerror("object class item expected")      def deleteitemwithname(self, name):         self.delete_tiem(item(name))      def savetofile(self):         open("list_of_items.bin", 'bw') f:             pickle.dump(self, f)      def loadfromfile(self):         open("list_of_items.bin", 'rb') f:             self.clear()             self.extend(pickle.load(f)) 

here problem part second py-file gui:

    def add_item():         try:             name = input_value1.get()             size = input_value2.get()             price = input_value3.get()             items_class.additemwithatributes(name, size, price)             output_value1.set("item added")         except valueerror:             output_value1.set("item not added")         items_class.savetofile()      def delete_item():         try:             name = input_value4.get()             #items_class.deleteitemwithatributes(name)             output_value1.set("item deleted")         except valueerror:             output_value1.set("item not deleted")         items_class.savetofile()