title: Python Tkinter Text Widget .get method error
body: <p>I'm very new to Python, sort of following Dive into Python 2 and wanted to dabble with some Tkinter programming. I've tried to make a little program that takes 3 sets of words and makes combinations of each word in the 3 sets to make keywords for websites. When I run the script, the GUI appears as expected, but I get the following error when I click on the Create Combinations button</p>
  
  <pre><code>Exception in Tkinter callback
  Traceback (most recent call last):
    File "/usr/lib/python2.6/lib-tk/Tkinter.py", line 1413, in __call__
      return self.func(*args)
    File "combomaker.py", line 34, in makeCombinations
      primaryraw = primaryKeyWordsBox.get()
  AttributeError: 'NoneType' object has no attribute 'get'
  </code></pre>
  
  <p>The code I'm trying to fix</p>
  
  <pre><code>#!/usr/bin/env python
  from Tkinter import *
  
  primaryKeyWordsLabel = None
  primaryKeyWordsBox = None
  secondaryKeyWordsLabel = None
  secondaryKeyWordsBox = None
  tertiaryKeyWordsLabel = None
  tertiaryKeyWordsBox = None
  
  class Application(Frame):
   def __init__(self, master=None, padx = 10, pady= 10):
    Frame.__init__(self, master)
    self.grid()
    self.createWidgets()
  
   def createWidgets(self):
    self.primaryKeyWordsLabel = LabelFrame(text="Primary Key Words", padx=10, pady=10)
    self.primaryKeyWordsLabel.grid()
    self.primaryKeyWordsBox = Text(primaryKeyWordsLabel, autoseparators=True, height=5, undo=True)
    self.primaryKeyWordsBox.grid()
    self.secondaryKeyWordsLabel = LabelFrame(text="Secondary Key Words", padx=10, pady=10)
    self.secondaryKeyWordsLabel.grid()
    self.secondaryKeyWordsBox = Text(secondaryKeyWordsLabel, autoseparators=True, height=5, undo=True)
    self.secondaryKeyWordsBox.grid()
    self.tertiaryKeyWordsLabel = LabelFrame(text="Tertiary Key Words", padx=10, pady=10)
    self.tertiaryKeyWordsLabel.grid()
    self.tertiaryKeyWordsBox = Text(tertiaryKeyWordsLabel, autoseparators=True, height=5, undo=True)
    self.tertiaryKeyWordsBox.grid()
    self.goButton = Button(text="Create Combinations", command=makeCombinations)
    self.goButton.grid()
  
  def makeCombinations():
    primaryraw = primaryKeyWordsBox.get()
    primary = primaryraw.split(', ')
    secondaryraw = secondaryKeyWordsBox.get()
    secondary = secondaryraw.split(', ')
    tertiaryraw = tertiaryKeyWordsBox.get()
    tertiary = tertiaryraw.split(', ')
    output=[]
    filename = "output.txt" 
    for i in range(len(primary)):
     for j in range(len(secondary)):
      for k in range(len(tertiary)):
       rawcombo=str(primary[i])+" "+str(secondary[j])+" "+str(tertiary[k])
       output.append(rawcombo)
    FILE = open(filename, w)
    for combo in output:
     FILE.write(combo+",\n")
    FILE.close()
  app = Application()                    
  app.master.title("Keyword Generator") 
  app.mainloop()    
  </code></pre>
  
  <p>I may have thrown myself into GUI programming too fast, this is my first attempt at any GUI work but not my first time programming.<br>
  Many thanks in advance :)</p>