Python Programming

import Tkinter as tk

class ProgramScreen(tk.Tk):
    def __init__(self,*args,**kwargs):
        tk.Tk.__init__(self,*args,**kwargs)
        container=tk.Frame(self)
        container.pack(expand=True, fill="both")
        container.grid_rowconfigure(0,weight=1)
        self.frames={}
        self.foo=tk.StringVar()
        for F in (Screen1,Screen2):
            page_name=F.__name__
            frame=F(parent=container,controller=self)
            self.frames[page_name]=frame
            frame.grid(row=0,column=0,sticky="nsew")
        self.show_frame("Screen1")
    def show_frame(self,page_name):
        frame=self.frames[page_name]
        frame.tkraise()
    def add(self,a,b):
        c=str(int(a)+int(b))
        self.foo.set(c)
        self.show_frame("Screen2")
class Screen1(tk.Frame):
    def __init__(self,parent,controller):
        tk.Frame.__init__(self,parent)
        self.controller=controller
        self.pack(fill="x",expand=1)
        entry1=tk.Entry(self)
        entry1.pack()
        entry2=tk.Entry(self)
        entry2.pack()
        button1=tk.Button(self,text="Lorem",command=lambda: controller.add(entry1.get(),entry2.get()))
        button1.pack()
class Screen2(tk.Frame):
    def __init__(self,parent,controller):
        tk.Frame.__init__(self,parent)
        self.controller=controller
        self.pack(fill="x",expand=1)
        label1=tk.Label(self,textvariable=controller.foo.get())
        label1.pack()

if __name__ == "__main__":
    app = ProgramScreen()
    app.mainloop()