Code:
# priorities.py
#   GUI program to manage priorities

from tkinter import *

class Priority:

    def __init__(self, subject, priority):
        self.subject = subject
        self.priority = priority

    def subject(self):
        return self.subject

    def priority(self):
        return self.priority


class GuiPart:

    def __init__(self):
        self.root = self.createWindow()

    def createWindow(self):

        root = Tk()
        root.resizable(width = False, height = False)
        root.title("Priorities")

        return root

    def display(self):

        listBox = Listbox().grid(row=1)

        buttonAdd = Button(text = "Add").grid(row = 2,
                                  column = 0,
                                  sticky = W,
                                  command = g.addItem)

        buttonRemove = Button(text="Remove").grid(row = 2,
                                   column = 0,
                                   sticky = W,
                                   command = g.removeItem)

        buttonEdit = Button(text="Edit").grid(row = 2,
                                 column = 0,
                                 sticky = E,
                                 command = g.editItem)

        textBox = Text().grid(row = 3)

    def addItem(self):
        item = Priority(self.subject, self.priority)
        item.subject = g.textBox.get("1.0", 'end-1c')

        g.listBox.insert(END, self)

class Client:
    pass

if __name__ == "__main__":
    g = GuiPart()
    g.display()
    g.root.mainloop()