title: How to make Tkinter checkbuttons work individually and default as checked
body: <p>I am trying to have a series of checkboxes which can be selected or not selected - then when the user presses the button, the letters allocated to the checkboxes should be added to an inputted string and then printed.</p>
  
  <p>I am having 2 major problems;</p>
  
  <ol>
  <li><p>The when the user presses a checkbox, all of the checkboxes are selected.</p></li>
  <li><p>I would like to have the default being that all of them as checked, but I cannot find how to do this. If this cannot be answered, it is less important than the 1st problem, and hence doesn't matter as much.</p></li>
  </ol>
  
  <p>This is my code so far;</p>
  
  <p>import Tkinter</p>
  
  <p>class MENU():</p>
  
  <pre><code>def __init__(self,NewData):
      self.SCREEN = Tkinter.Tk()
      self.NewData = NewData
      self.Selection = {"A":1,"B":1,"C":1,"D":1}     
      self.A = Tkinter.Checkbutton(self.SCREEN,text="A",variable=self.Selection["A"]).pack()
      self.B = Tkinter.Checkbutton(self.SCREEN,text="B",variable=self.Selection["B"]).pack()
      self.C = Tkinter.Checkbutton(self.SCREEN,text="C",variable=self.Selection["C"]).pack()
      self.D = Tkinter.Checkbutton(self.SCREEN,text="D",variable=self.Selection["D"]).pack()
  
      self.BtnFinish = Tkinter.Button(self.SCREEN,text="Finish selection",command=self.FinishSelection)
      self.BtnFinish.pack()
  
      self.SCREEN.mainloop()
  
  def FinishSelection(self):
      SelectionString = ""
      for n in self.Selection:
          if self.Selection[n]:
              SelectionString+=n
      self.NewData+="\nQuestions\n"+SelectionString+"\n"
      print self.NewData
  </code></pre>
  
  <p>MENU("")</p>
  
  <p>If it matters at all, this is for Python 2.7.3. Additionally, my thanks, and also apologies to those of you who likely have to point out something incredibly obvious/basic, which, as a beginner for Tkinter, I have not realised.</p>