import Tkinter

class MainWindow(Tkinter.Tk):
    def __init__(self):
        Tkinter.Tk.__init__(self)

        self.lb = Tkinter.Listbox(self, selectmode=Tkinter.MULTIPLE)
        self.lb.pack()
        for x in range(10):
            self.lb.insert(Tkinter.END, str(x+5))

        self.bind('<Return>', self.cb_curselection)

    def cb_curselection(self, event=None):
        print(repr(self.lb.curselection()))


root = MainWindow()
root.mainloop()