title: AttributeError: 'NoneType' object has no attribute 'delete'
body: <p>I have run into this issue and I can't understand why.</p>
  
  <p>I took my code from my application and made this test code so you don't have to go through a bunch of junk to see what I am asking.</p>
  
  <p>I have this working in other code. But after comparing the two, I can't for the life of me figure this out.</p>
  
  <p>In this application, I get the error "AttributeError: 'NoneType' object has no attribute 'delete' ".</p>
  
  <pre><code>import Tkinter as tk
  
  def main():
      mainWindow = tk.Tk()
      v = tk.StringVar()
      entryBox = tk.Entry(mainWindow, textvariable=v).grid(column=0, row=1)
      def test():
          entryBox.delete(0,20)
      testButton = tk.Button(mainWindow, text='Go!', command=test, padx=10).grid(row=2, column=0) 
      tk.mainloop()
  main()
  </code></pre>