import Tkinter as Tk
import tkSimpleDialog

class Dialog(tkSimpleDialog.Dialog):

    def body(self, master):
        entry = Tk.Entry(master)
        entry.pack()
        return entry

    def apply(self):
    	raise RuntimeError

root = Tk.Tk()

button = Tk.Button(root, text="test", command=lambda: Dialog(root))
button.pack()

root.mainloop()