python beginner: interaction of classes

What is the problem in the below code? I think due to the last argument it throws exception when calling menubar?

The app is supposed to be a simple text editor and I want to have the menu declaration in a separate class. When I run the script, the textfield gets generated successfully, but without menubar. When I quit the application, the following error message occurs.

Traceback (most recent call last):
  File "", line 41, in <module>
    menu = Menubar(window, textfield.text)
  File "", line 20, in __init__
    menubar = Menu(window)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/", line 2580, in __init__
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk/", line 1974, in __init__
_tkinter.TclError: this isn't a Tk applicationNULL main window

from Tkinter import *
import tkFileDialog

class Textfield(object):
  def __init__(self, window):
    self.window = window
    window.title("text editor")
    self.scrollbar = Scrollbar(window)
    self.text = Text(window,yscrollcommand=self.scrollbar.set)

class Menubar(object):   
  def __init__(self, window, text):
    self.window = window
    self.text = text
    menubar = Menu(window)
    filemenu = Menu(menubar)
    filemenu.add_command(label="save as",command=self.saveas)

  def load(self):
    self.file = tkFileDialog.askopenfile()
    self.text.delete(1.0, END)
    if self.file:

  def saveas(self):
    self.file = tkFileDialog.asksaveasfile()
    if self.file:
      self.file.write(self.text.get(1.0, END))

window =  Tk()            
textfield = Textfield(window)
menu = Menubar(window, textfield.text)


Main application loop (window.mainloop()) must be started after all the other statements in the program. When you create menu, your main window is already destroyed.

    window.mainloop()    # Remove this line


window =  Tk()            
textfield = Textfield(window)
menu = Menubar(window, textfield.text)
window.mainloop()    # <----

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