from Tkinter import *
globalFilename = ""
class Master:
    def __init__(self, top):
        self.filename = ""
        frame_e = Frame(top)
        frame_e.pack()
        self.t_filename = StringVar()

        entry = Entry(frame_e, textvariable=self.t_filename, bg="white")
        entry.pack()
        entry.focus_force()

        saveButton = Button(frame_e, text="Save", command=self.on_button)
        saveButton.pack(side=BOTTOM, anchor=S)


    def on_button(self):
        self.filename = self.t_filename.get()
        print self.filename
        root.quit()
        root.destroy()


root = Tk()
root.geometry("100x100+100+50")

M = Master(root)
print M.filename
root.mainloop( )
print M.filename
globalFilename = M.filename
print globalFilename