class - python beginner: interaction of classes -

what problem in below code? think due last argument throws exception when calling menubar?

the app supposed simple text editor , want have menu declaration in separate class. when run script, textfield gets generated successfully, without menubar. when quit application, following error message occurs.

""" traceback (most recent call last):   file "editor_play.py", line 41, in <module>     menu = menubar(window, textfield.text)   file "editor_play.py", line 20, in __init__     menubar = menu(window)   file "/system/library/frameworks/python.framework/versions/2.7/lib/python2.7/lib-tk/tkinter.py", line 2580, in __init__   file "/system/library/frameworks/python.framework/versions/2.7/lib/python2.7/lib-tk/tkinter.py", line 1974, in __init__ _tkinter.tclerror: isn't tk applicationnull main window """  tkinter import * import tkfiledialog  class textfield(object):   def __init__(self, window):     self.window = window     window.title("text editor")     self.scrollbar = scrollbar(window)     self.scrollbar.pack(side="right",fill="y")     self.text = text(window,yscrollcommand=self.scrollbar.set)     self.scrollbar.config(command=self.text.yview)     self.text.pack()     window.mainloop()   class menubar(object):      def __init__(self, window, text):     self.window = window     self.text = text     menubar = menu(window)     filemenu = menu(menubar)     filemenu.add_command(label="load",command=self.load)     filemenu.add_command(label="save as",command=self.saveas)     menubar.add_cascade(label="file",menu=filemenu)     window.config(menu=menubar)    def load(self):     self.file = tkfiledialog.askopenfile()     self.text.delete(1.0, end)     if self.file:       self.text.insert(1.0, self.file.read())    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 started after other statements in program. when create menu, main window destroyed.

    self.scrollbar.config(command=self.text.yview)     self.text.pack()     window.mainloop()    # remove line  ...  window =  tk()             textfield = textfield(window) menu = menubar(window, textfield.text) window.mainloop()    # <----