title: Make clear button backspace by one in python tkinter calculator
body: <p>I am making a calculator in python using tkinter. The calculator works very well apart from one thing. At the moment I have set the calculator to clear the display. I want to make it so that it clears the last number on the display. For example 564 would become 56.</p>
  
  <p>Any help greatly appreciated.</p>
  
  <pre><code>#Import tkinter
  from Tkinter import *
  #Setup quit button
  def quit():
      window.destroy()
  #What happens when you click the button
  def buttonclick(event):
      global calcvalue
      global savedvalue
      global operator
      pressed = ""
      if event.x &gt;10 and event.x &lt;70 and event.y &gt; 50 and event.y &lt; 110 : pressed = 7
      if event.x &gt;10 and event.x &lt;70 and event.y &gt; 120 and event.y &lt; 180 : pressed = 4
      if event.x &gt;10 and event.x &lt;70 and event.y &gt; 190 and event.y &lt; 250 : pressed = 1
      if event.x &gt;10 and event.x &lt;70 and event.y &gt; 260 and event.y &lt; 320 : pressed = 0
      if event.x &gt;80 and event.x &lt;140 and event.y &gt; 50 and event.y &lt; 110 : pressed = 8
      if event.x &gt;80 and event.x &lt;140 and event.y &gt; 120 and event.y &lt; 180 : pressed = 5
      if event.x &gt;80 and event.x &lt;140 and event.y &gt; 190 and event.y &lt; 250 : pressed = 2
      if event.x &gt;150 and event.x &lt;210 and event.y &gt; 50 and event.y &lt; 110 : pressed = 9
      if event.x &gt;150 and event.x &lt;210 and event.y &gt; 120 and event.y &lt; 180 : pressed = 6
      if event.x &gt;150 and event.x &lt;210 and event.y &gt; 190 and event.y &lt; 250 : pressed = 3
      if event.x &gt;80 and event.x &lt;140 and event.y &gt; 260 and event.y &lt; 320 : pressed = "equals"
      if event.x &gt;150 and event.x &lt;210 and event.y &gt; 260 and event.y &lt; 320 : pressed = "clear"
      if event.x &gt;220 and event.x &lt;280 and event.y &gt; 50 and event.y &lt; 110 : pressed = "divide"
      if event.x &gt;220 and event.x &lt;280 and event.y &gt; 120 and event.y &lt; 180 : pressed = "times"
      if event.x &gt;220 and event.x &lt;280 and event.y &gt; 190 and event.y &lt; 250 : pressed = "minus"
      if event.x &gt;220 and event.x &lt;280 and event.y &gt; 260 and event.y &lt; 320 : pressed = "plus"
  
  
      if pressed == 0 or pressed == 1 or pressed == 2 or pressed == 3 or pressed == 4 or pressed == 5 or pressed == 6 or pressed == 7 or pressed == 8 or pressed == 9 :
          calcvalue = calcvalue * 10 + pressed
  
  
      if pressed == "divide" or pressed == "times" or pressed == "minus" or pressed == "plus" :
          operator = pressed
          savedvalue = calcvalue
          calcvalue = 0
  
      if pressed == "equals":
          if operator == "divide": calcvalue =  savedvalue /calcvalue
          if operator == "times": calcvalue =  savedvalue * calcvalue
          if operator == "minus": calcvalue =  savedvalue - calcvalue
          if operator == "plus": calcvalue =  savedvalue + calcvalue
  
      if pressed == "clear":
          calcvalue = 0
  
      displayupdate()
      canvas.update()
  
  #Setup the display
  def displayupdate():
      canvas.create_rectangle(10, 10, 370, 40, fill="white", outline="black")
      canvas.create_text(350, 25,  text=calcvalue,font="Times 20  bold",anchor=E)
  
  #Setup the canvas/window
  def main():
      global window
      global tkinter
      global canvas
      window = Tk()
      window.title("BIG Calculator")
      Button(window, text="Quit",  width=5, command=quit).pack()
      canvas = Canvas(window, width= 380, height=330, bg = 'black')
      canvas.bind("&lt;Button-1&gt;", buttonclick)
  
  #Add the 1 2 3 4 5 6 7 8 9 0 buttons
      canvas.create_rectangle(10, 50, 100, 110, fill="white", outline="black")
      canvas.create_text(45, 80,  text="7",font="Times 30  bold")
  
      canvas.create_rectangle(10, 120, 100, 180, fill="white", outline="black")
      canvas.create_text(45, 150,  text="4",font="Times 30  bold")
  
      canvas.create_rectangle(10, 190, 100, 250, fill="white", outline="black")
      canvas.create_text(45, 220,  text="1",font="Times 30  bold")
  
      canvas.create_rectangle(10, 260, 100, 320, fill="white", outline="black")
      canvas.create_text(45, 290,  text="0",font="Times 30  bold")
  
      canvas.create_rectangle(80, 50, 170, 110, fill="white", outline="black")
      canvas.create_text(115, 80,  text="8",font="Times 30  bold")
  
      canvas.create_rectangle(80, 120, 170, 180, fill="white", outline="black")
      canvas.create_text(115, 150,  text="5",font="Times 30  bold")
  
      canvas.create_rectangle(80, 190, 170, 250, fill="white", outline="black")
      canvas.create_text(115, 220,  text="2",font="Times 30  bold")
  
      canvas.create_rectangle(150, 50, 240, 110, fill="white", outline="black")
      canvas.create_text(185, 80,  text="9",font="Times 30  bold")
  
      canvas.create_rectangle(150, 120, 240, 180, fill="white", outline="black")
      canvas.create_text(185, 150,  text="6",font="Times 30  bold")
  
      canvas.create_rectangle(150, 190, 240, 250, fill="white", outline="black")
      canvas.create_text(185, 220,  text="3",font="Times 30  bold")
  
  #SHow the = c + - x / buttons
      canvas.create_rectangle(80, 260, 170, 320, fill="white", outline="black")
      canvas.create_text(115, 290,  text="=",font="Times 30  bold")
  
      canvas.create_rectangle(150, 260, 240, 320, fill="white", outline="black")
      canvas.create_text(185, 290,  text="C",font="Times 30  bold")
  
      canvas.create_rectangle(220, 50, 370, 110, fill="white", outline="black")
      canvas.create_text(295, 80,  text="Divide",font="Times 30  bold")
  
      canvas.create_rectangle(220, 120, 370, 180, fill="white", outline="black")
      canvas.create_text(295, 150,  text="Times",font="Times 30  bold")
  
      canvas.create_rectangle(220, 190, 370, 250, fill="white", outline="black")
      canvas.create_text(295, 220,  text="Minus",font="Times 30  bold")
  
      canvas.create_rectangle(220, 260, 370, 320, fill="white", outline="black")
      canvas.create_text(295, 290,  text="Plus",font="Times 30  bold")
  
  #Make the whole calculator work
      canvas.create_rectangle(10, 10, 280, 40, fill="white", outline="black")
      global calcvalue
      calcvalue = 0
      displayupdate()
  
      canvas.pack()
      window.mainloop()
  
  
  
  
  
  
  
  main()
  </code></pre>