Python tkinter entry event

Tkinter Event Binding

Summary: 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 called event binding. When the event occurs, the assigned function is invoked automatically.

In the previous tutorial, you learned how to bind a function to an event of a widget via the command option. However, not all Tkinter widgets support the command option.

Therefore, Tkinter provides you with an alternative way for event binding via the bind() method. The following shows the general syntax of the bind() method:

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

When an event occurs in the widget , Tkinter will invoke the handler automatically with the event detail.

If you want to register an additional handler, you can pass the ‘+’ to the add argument. It means that you can have multiple event handlers that respond to the same event.

Tkinter event binding examples

The following program illustrates how to bind the return_pressed function to the Return key pressed event of the ‘Save’ 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()Code language: Python (python)

In this example, the following statement calls the bind() method on the button widget to bind the Return key pressed event:

btn.bind('Return>', return_pressed)Code language: HTML, XML (xml)

The following example illustrates 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()Code language: Python (python)

When you move the focus to the button and press the Return key, Tkinter automatically invokes the return_pressed and log functions.

The following binds the log() function to the Return key pressed event of the ‘Save’ button:

btn.bind('', log, add='+')Code language: Python (python)

In this statement, the third argument add=’+’ registered additional handler, which is the log() function.

If you don’t specify the add=’+’ argument, the bind() method will replace the existing handler ( return_pressed ) by the new one ( log ).

Event patterns

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

The following shows the general syntax of an event pattern:

modifier-type-detail>Code language: HTML, XML (xml)

In this syntax, an event is surrounded by angle brackets ( <> ). Inside the angle brackets, there are zero or more modifiers, an event type, and detailed information about the event.

For example, the denotes a keyboard press of the key A . and represents a keypress of Alt + Ctrl + Delete .

The following section shows the most commonly used event modifiers, event types, and event details.

1) Event modifiers

The following table lists the most commonly used event modifiers:

Event Modifier	Meaning
Alt	The Alt key is held
Control	The Ctrl key is held
Shift	The Shift key is held
Any	This modifier makes an event type general. For example, the event pattern applies to the keypress of any key.

Event types

The following table shows the most commonly used event types:

Type	Name	Description
36	Activate	The state option of a widget changes from inactive to active.
4	Button	One mouse button is pressed
5	ButtonRelease	One mouse button is released
22	Configure	The size of the widget is changed
37	Deactivate	The state option of a widget changes from active to inactive.
17	Destroy	A widget is being destroyed.
7	Enter	The mouse pointer is moved into a visible part of a widget.
12	Expose	Some part of the widget or application is visible after having been covered up by another window.
9	FocusIn	The input focus was moved into a widget.
10	FocusOut	The input focus was moved out of a widget.
2	KeyPress	A key is pressed.
3	KeyRelease	A key is released
8	Leave	The mouse pointer is moved out of a widget.
19	Map	A widget is being placed on a container e.g., calling the pack() or grid() method.
6	Motion	The mouse pointer is moved entirely within a widget.
38	MouseWheel	The user moved the mouse wheel up or down.
18	Unmap	A widget is being unmapped and is no longer visible, for example when calling the grid_remove() method on the widget.
15	Visibility	At least some part of the application window becomes visible on the screen.

Event Detail

The following table shows several ways to name keys:

.keysym	.keycode	.keysym_num	Key
Alt_L	64	65513	The left-hand alt key
Alt_R	113	65514	The right-hand alt key
BackSpace	22	65288	backspace
Cancel	110	65387	break
Caps_Lock	66	65549	CapsLock
Control_L	37	65507	The left-hand control key
Control_R	109	65508	The right-hand control key
Delete	107	65535	Delete
Down	104	65364	↓
End	103	65367	end
Escape	9	65307	esc
Execute	111	65378	SysReq
F1	67	65470	Function key F1
F2	68	65471	Function key F2
Fi	66+i	65469+i	Function key Fi
F12	96	65481	Function key F12
Home	97	65360	home
Insert	106	65379	insert
Left	100	65361	←
Linefeed	54	106	Linefeed (control-J)
KP_0	90	65438	0 on the keypad
KP_1	87	65436	1 on the keypad
KP_2	88	65433	2 on the keypad
KP_3	89	65435	3 on the keypad
KP_4	83	65430	4 on the keypad
KP_5	84	65437	5 on the keypad
KP_6	85	65432	6 on the keypad
KP_7	79	65429	7 on the keypad
KP_8	80	65431	8 on the keypad
KP_9	81	65434	9 on the keypad
KP_Add	86	65451	+ on the keypad
KP_Begin	84	65437	The center key (same key as 5) on the keypad
KP_Decimal	91	65439	Decimal ( . ) on the keypad
KP_Delete	91	65439	delete on the keypad
KP_Divide	112	65455	/ on the keypad
KP_Down	88	65433	↓ on the keypad
KP_End	87	65436	end on the keypad
KP_Enter	108	65421	enter on the keypad
KP_Home	79	65429	home on the keypad
KP_Insert	90	65438	insert on the keypad
KP_Left	83	65430	← on the keypad
KP_Multiply	63	65450	× on the keypad
KP_Next	89	65435	PageDown on the keypad
KP_Prior	81	65434	PageUp on the keypad
KP_Right	85	65432	→ on the keypad
KP_Subtract	82	65453	— on the keypad
KP_Up	80	65431	↑ on the keypad
Next	105	65366	PageDown
Num_Lock	77	65407	NumLock
Pause	110	65299	pause
Print	111	65377	PrintScrn
Prior	99	65365	PageUp
Return	36	65293	Enter key
Right	102	65363	→
Scroll_Lock	78	65300	ScrollLock
Shift_L	50	65505	The left-hand shift key
Shift_R	62	65506	The right-hand shift key
Tab	23	65289	The tab key

Binding events to root window

So far, you have learned how to bind an event to a particular widget. Tkinter also allows you to bind an event to the top-level window.

In this case, the syntax for the bind() is the same except that you can call it on the root window like this:

root.bind('Return>', handler)Code language: HTML, XML (xml)

The levels of binding

In the previous example, you have learned how to bind an event to a particular instance of a widget. This is called an instance-level binding.

Tkinter also allows you to bind an event to all the instances of a widget. For example, you can bind the event to all the textboxes in a program:

root.bind_class('Entry', '', paste)Code language: JavaScript (javascript)

By the way, you use the Entry widget to create a textbox in Tkinter.

This is called class-level binding because you bind the event to a class instead of an instance.

Unbinding events

Sometimes, you may want to undo the effect of an earlier binding. To do it, you can use the unbind() method:

widget.unbind(event)Code language: CSS (css)

The following example unbinds the event from the btn button:

btn.unbind('Return>')Code language: HTML, XML (xml)

Summary

• Use the bind() method to bind an event to a widget.
• Tkinter supports both instance-level and class-level bindings.

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