#!/usr/bin/env python
import tkinter as T


class SubWin(T.Toplevel):
    def __init__(self, *args, **kwargs):
        T.Toplevel.__init__(self, *args, **kwargs)
        self.title('Yeah')
        self.geometry('300x50')

        self.label = T.Label(self, text='Hallo Unterfenster.')
        self.label.pack(side=T.TOP)
        
        self.button = T.Button(self, text="Exit", command=self.destroy)
        self.button.pack(side=T.TOP)


class MainWin(T.Tk):
    def __init__(self, *args, **kwargs):
        T.Tk.__init__(self, *args, **kwargs)
        
        self.button = T.Button(self, text="Exit", command=self.destroy)
        self.button.pack(side=T.TOP)
        
        self.button = T.Button(self, text="Subbie", command=self.subbie)
        self.button.pack(side=T.TOP)
        
        self.frame = T.Frame(self, relief='ridge', borderwidth=5)
        self.frame.pack(side=T.TOP, fill='both', expand=1)

    def subbie(self):
        SubWin()


if __name__ == '__main__':
    MainWin().mainloop()