Binding levels

In the previous section, you had a look at how to bind an event to an instance of a widget. This can be called an instance-level binding.

However, there may be times when you need to bind events to an entire application. At times, you may want to bind an event to a particular class of widget. Tkinter provides the following levels of binding options for this:

• Application-level binding: Application-level bindings let you use the same binding across all windows and widgets of an application as long as any one window of the application is in focus. The syntax for application-level bindings is as follows:

widget.bind_all(event, callback, add=None)

The typical usage pattern is as follows:

root.bind_all('<F1>', show_help)

Application-level binding here means that, irrespective of the widget that is currently under focus, pressing the F1 key will always trigger the show_help callback as long as the application is in focus.

• Class-level binding: You can also bind events at a particular class level. This is normally used to set the same behavior for all instances of a particular widget class. The syntax for class-level binding is as follows:

w.bind_class(class_name, event, callback, add=None)

The typical usage pattern is as follows:

my_entry.bind_class('Entry', '<Control-V>', paste)

In the preceding example, all the entry widgets will be bound to the <Control-V> event, which will call a method named paste (event).