title: 'NoneType' object has no attribute 'children'
body: <p>I have a bunch of problems here. When I run code, it creates a window as should. But when I try to close it, I get "'NoneType' object has no attribute 'children'". Also, when writing text in boxes, text appeares in all three boxes. What am I doing wrong?</p>
  
  <pre><code>from Tkinter import *
  
  class Window(Frame):
      def __init__(self, master=None):
          self.root = Tk()
          Frame.__init__(self, master)
          self.master = master
          self.init_window()
          self.root.geometry("400x300")
          self.root.mainloop()
  
      def init_window(self):
          self.root.title("GUI")
          self.ins = StringVar
          self.dele = StringVar
          self.upd = StringVar
          self.b1 = Button(self.root, text='insert(name,info,date)')
          self.b1.grid(row=0,column=0)
          self.b2 = Button(self.root, text='delete')
          self.b2.grid(row=1, column=0)
          self.b3 = Button(self.root, text='update')
          self.b3.grid(row=2, column=0)
          self.e1 = Entry(self.root, textvariable=self.ins)
          self.e1.grid(row=0, column=1)
          self.e2 = Entry(self.root, textvariable=self.dele)
          self.e2.grid(row=1, column=1)
          self.e3 = Entry(self.root, textvariable=self.upd)
          self.e3.grid(row=2, column=1)
          a = self.e1.get()
          b = self.e2.get()
          c = self.e3.get()
  
  Window()
  </code></pre>
  
  <p><a href="http://i.stack.imgur.com/hMaQo.png" rel="nofollow">Here is the screenshot</a></p>