title: Tkinter checkbutton bind does not take the updated value
body: <p>I have defined two checkbutton labels: (var is the class I use so that I have access to the variables outside as well)</p>
  
  <pre><code>lby = ttk.Checkbutton(var.frame,text="y-direction",variable=var.vel_y)
  lbz = ttk.Checkbutton(var.frame,text="z-direction",variable=var.vel_z)
  lby.grid(column=1,row=3,sticky=W)
  lbz.grid(column=1,row=4,sticky=W)
  </code></pre>
  
  <p>Now, I bind the user-click on any of the buttons to call a function options_yz().</p>
  
  <pre><code> def options_yz(key):
      print("y"+str(var.vel_y.get()))
      print("z"+str(var.vel_z.get()))
   lby.bind('&lt;Button-1&gt;', options_yz)
   lbz.bind('&lt;Button-1&gt;', options_yz)
  </code></pre>
  
  <p>But it seems to me that the button-click calls the function before changing the value of the variable. Is there any way to call the function after changing the variable?</p>
  
  <p>For example:
  The default values for var.vel_y and var.vel_z are 0. I click on the checkbutton for y-direction. My output is:</p>
  
  <pre><code>y0
  z0
  </code></pre>
  
  <p>My actual output should be:</p>
  
  <pre><code>y1
  z0
  </code></pre>
  
  <p>Next I click on the checkbutton for z-direction. My output is:</p>
  
  <pre><code>y1
  z0
  </code></pre>
  
  <p>My actual output should be:</p>
  
  <pre><code>y1
  z1
  </code></pre>