title: TypeError: callback() takes exactly 2 arguments (0 given)
body: <p>I get this error every time I click a button using Tkinter. I'm not quite sure what it means that 0 arguments are given, because I thought that callback gives two arguments. Traceback of the error:</p>
  
  <pre><code>Exception in Tkinter callback Traceback (most recent call last): 
    File "C:\Python27\lib\lib-tk\Tkinter.py", line 1470, in call return self.func(*args)   
  TypeError: callback() takes exactly 2 arguments (0 given)
  </code></pre>
  
  <p>Here is all my code related to callback</p>
  
  <pre><code>def callback(input_set, user_set):
      user_score = 0
      if len(input_set &amp; user_set) == 0:
          user_score += len(input_set - user_set) * 2
      for multiplier, user_set in enumerate(user_sets, 1):
          user_score += len(input_set &amp; user_set) * multiplier
  
      print "Congratulations, you've scored " + str(user_score) + " points!"
  
  # Creates button to calculate score
  self.button = Tkinter.Button(self, font="Arial", text="Click to get your score", 
                               width = 45, pady = 5, command = callback)
  self.button.grid(column=0, row=3, sticky="", columnspan=2)
  </code></pre>