Tkinter Event Binding

In this tutorial, you’ll learn about the Tkinter event binding mechanism.

Introduction to the Tkinter Event Binding

Assigning a function to an event of a widget is known as event binding. The assigned function is invoked automatically when the event occurs.

Unlike the command option, not all Tkinter widgets support it, so Tkinter provides an alternative way for event binding via the bind() method.

Using the bind() Method

The general syntax of the bind() method is:

widget.bind(event, handler, add=None)

When an event occurs in the widget, Tkinter will automatically invoke the handler with the event details. You can register additional handlers by passing '+' to the add argument, allowing multiple event handlers for the same event.

Tkinter Event Binding Examples

Example 1: Binding a Function to a Key Event

Here’s how to bind a function to the Return key pressed event of a button:

import tkinter as tk
from tkinter import ttk

def return_pressed(event):
    print('Return key pressed.')

root = tk.Tk()
btn = ttk.Button(root, text='Save')
btn.bind('', return_pressed)

btn.focus()
btn.pack(expand=True)
root.mainloop()

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Example 2: Registering Multiple Handlers

This example shows how to use the bind() method to register multiple handlers for the same event:

import tkinter as tk
from tkinter import ttk

def return_pressed(event):
    print('Return key pressed.')

def log(event):
    print(event)

root = tk.Tk()
btn = ttk.Button(root, text='Save')
btn.bind('', return_pressed)
btn.bind('', log, add='+')

btn.focus()
btn.pack(expand=True)
root.mainloop()

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Event Patterns

Tkinter uses event patterns to map event names with handlers. For example, <Return> denotes the Return key pressed.

The syntax for event patterns is:

<modifier-type-detail>

Modifiers can include:

• Alt: The Alt key is held
• Control: The Ctrl key is held
• Shift: The Shift key is held
• Any: Applies to the keypress of any key, e.g., <Any-KeyPress>

Binding Events to the Root Window

You can also bind an event to the top-level window:

root.bind('<Return>', handler)

Unbinding Events

If you want to undo the effect of an earlier binding, use the unbind() method:

btn.unbind('<Return>')

Conclusion

In this tutorial, you learned about Tkinter event binding and how to use the bind() method to create responsive applications. You also explored binding events to both individual widgets and the root window, and how to manage multiple handlers for the same event.