Accessing widgets defined inside the Kv language in your Python code

This recipe will teach you how to access definitions inside the Kv language in your Python code and vice versa.

Getting ready

This recipe will use button, a very common widget that we also used in the last recipe.

How to do it…

This recipe follows as:

1. Make a rule for the widget.
2. Define a button.
3. Give it an ID.
4. Define the label for the button.
5. In the action, call a method in the Python code:

   <MyW>:
       Button:
           id: b1
           text: 'Press to smash'
           on_release: root.b_smash()

6. Create the Python code with the method:

   import kivy
   kivy.require('1.8.0') # replace with your current kivy version !
   
   from kivy.app import App
   from kivy.uix.widget import Widget
   
   class MyW(Widget):
       def b_smash(self):
           self.ids.b1.text = 'Pudding'
   
   class e7App(App):
       def build(self):
           return MyW()
   
   if __name__ == '__main__':
       e7App().run()

How it works…

In the Kv Language file, we have the following in the first line:

<MyW>:

This is the name of the widget, a simple button. The second line is:

Button:

This is the button definition. The third line is:

id: b1

This gives the button an ID b1. The fourth line is:

    text: 'Press to smash'

This makes the initial text on the button 'Press to smash'. The fifth line is:

    on_release: root.b_smash()

The preceding line is making a call to the Python code; it refers the method b_smash() of the root class MyW.

The fifth line in the Python code is:

class MyW(Widget):

This is the definition of the class related to the Widget. The sixth line is:

def b_smash(self):

This defines the method b_smash(), which is accessed by the Kv language file. The seventh line is:

self.ids.b1.text = 'Pudding'

This accesses the widget defined in the Kv language file, specifically the button with its ID, and changes the text displayed in the button to the text Pudding.

See also

If you want to run your interface, take a look at our recipe Running your code, and to get more details about widgets, see the recipes in Chapter 4, Widgets.