title: Since the rectangle is not a button, then how can I create a callback function to print('something') after clicking on that rectangle?
body: <p>I have a rectangle in a canvas. Since the rectangle is not a button, then how can I create a callback function to print('something') after clicking on that rectangle?</p>
  <p>In a button I can use <code>on_release</code> to call a function, but in rectangle how should I call a function after clicking on that rectangle?</p>
  <pre class="lang-py prettyprint-override"><code>import kivy
  from kivy.app import App
  from kivy.lang import Builder
  from kivy.uix.widget import Widget
  #from kivy.graphics import *
  from kivy.core.window import Window
  from kivy.uix.screenmanager import ScreenManager, Screen
  from kivy.animation import Animation
  from kivy.uix.button import Button
  from kivy.uix.gridlayout import GridLayout
  from kivy.clock import Clock
   
  
  Builder.load_string('''
    
   
  &lt;main&gt;:
        
       
      RelativeLayout :
           
          size: root.width,root.height
  
           
          canvas:
          
              Color:
                  rgba:196/255, 195/255, 49/255,1
              Rectangle:
                  size:470,root.height
             
  ''')
  
  
  
  
  class main(Screen):
       pass
      
          
   
  class test(App):
      def build(self):
         
          sm = sm = ScreenManager()
          sm.add_widget(main(name='main'))
          Window.clearcolor=(55/255, 77/255, 33/255)
          return sm 
  
  if __name__=='__main__':
      test().run()
  </code></pre>