Communication between python objects?

Question

Communication between objects

The idea is create a Toplevel window from Gui and after Toplevel closed send the data (name) from Toplevel Entry back to Gui

How object app can know whether the toplev object was destroyed?

or with other words

How can object of Gui know that the object of My_Toplevel is closed?

from tkinter import *
font1 = font=("Open Sans Standard",16,"bold")

class My_Toplevel():
    def __init__(self, master=None):
        self.master = master
        self.toplev = Toplevel(master)
        self.name = None
        self.create_widgets()
    def create_widgets(self):
        self.entry_name = Entry(self.toplev, font=font1)
        self.button_ok = Button(self.toplev, text="Ok", font=font1,
                                command=self.get_name)
        self.entry_name.pack()
        self.button_ok.pack()
    def get_name(self):
        self.name = self.entry_name.get()
        self.toplev.destroy()

class Gui(Frame):
    def __init__(self, master):
        Frame.__init__(self, master)
        self.pack()
        self.master = master
        self.label_text = Label(self, text="Foo Bar Window", font=font1)
        self.label_text.pack()
        self.button_toplevel = Button(self, text="Create Toplevel", 
                                command=self.get_toplevel, font=font1)
        self.button_toplevel.pack()

    def get_toplevel(self):
        self.my_top = My_Toplevel(self)

if __name__ == "__main__":
    root = Tk()
    root.title("Parent")
    app = Gui(root)
    root.mainloop()

Answer 1

You need to pass the data to the Gui instance before you destroy My_Toplevel . One way to do that is to save the name string as an attribute of the Gui instance since you pass that the master parameter when you call My_Toplevel . For example:

from tkinter import *
font1 = font=("Open Sans Standard",16,"bold")

class My_Toplevel():
    def __init__(self, master=None):
        self.master = master
        self.toplev = Toplevel(master)
        self.create_widgets()

    def create_widgets(self):
        self.entry_name = Entry(self.toplev, font=font1)
        self.button_ok = Button(self.toplev, text="Ok", font=font1,
                                command=self.get_name)
        self.entry_name.pack()
        self.button_ok.pack()

    def get_name(self):
        self.master.name_data = self.entry_name.get()
        self.toplev.destroy()

class Gui(Frame):
    def __init__(self, master):
        Frame.__init__(self, master)
        self.pack()
        self.master = master
        self.label_text = Label(self, text="Foo Bar Window", font=font1)
        self.label_text.pack()
        self.button_toplevel = Button(self, text="Create Toplevel", 
                                command=self.get_toplevel, font=font1)
        self.button_toplevel.pack()

        self.name_data = None
        Button(self, text="show name", command=self.show_name).pack()

    def show_name(self):
        print("Name =", self.name_data)

    def get_toplevel(self):
        self.my_top = My_Toplevel(self)

if __name__ == "__main__":
    root = Tk()
    root.title("Parent")
    app = Gui(root)
    root.mainloop()

Press the "show name" button to print the name string to the console.

If you need to save more than a single string, you could append the name to a list, save it in a dictionary, etc.

If you like, you can call the Gui.show_name method just before the TopLevel window is destroyed:

def get_name(self):
    self.master.name_data = self.entry_name.get()
    self.master.show_name()
    self.toplev.destroy()