2.1 A small lexicon of widgets - Part 1

Now we’re ready to present a systematized set of some of the tkinter widgets. We aren’t able to describe all of them, however – it would bloat our course to an unmanageable size. We’re convinced that our collection is large enough to make you familiar with tkinter standards and habits, and at the same time will encourage you to carry out your own experiments and tests.

You already know some of the widgets. In these cases, we’ll limit our descriptions to the necessary minimum.

Each tkinter widget is created by a constructor of its class. The very first argument of the constructor invocation is always the master widget i.e., the widget that owns the newly created object.

widget = Widget(master, option, ... )

The master widget is just the main window in most cases, but can be also a Frame or a LabelFrame (described in the next section).

The constructor accepts a set of arguments that configure the widget. Different widgets use different sets of arguments.

As we mentioned before, all widgets fall into two categories: clickable and non-clickable. We’ll start with the first.

We think the Button doesn’t require any special attention, as we’ve used it many times before. You already know what it looks like and how it works, so we’re going to limit ourselves to enumerating the most usable properties of the widget, along with its specific methods.

Analyze and run the code in the editor – we wrote it to show you some of the button’s properties and methods in action.

import tkinter as tk
 
 
def switch():
    if button_1.cget('state') == tk.DISABLED:
        button_1.config(state=tk.NORMAL)
        button_1.flash()
    else:
        button_1.flash()
        button_1.config(state=tk.DISABLED)
 
 
def mouseover(ev):
    button_1['bg'] = 'green'
 
 
def mouseout(ev):
    button_1['bg'] = 'red'
 
 
window = tk.Tk()
button_1 = tk.Button(window, text="Enabled", bg="red")
button_1.bind("<Enter>", mouseover)
button_1.bind("<Leave>", mouseout)
button_1.pack()
button_2 = tk.Button(window, text="Enable/Disable", command=switch)
button_2.pack()
window.mainloop()

The Checkbutton is a two-state switch that can be ticked (checked) or not; thus, it is a handy tool to represent yes/no user choices.

Let's start with its properties: And now some of its methods:

Take a look at the code in the editor pane. The sample we’ve prepared for you makes use of the checkbutton and does two things:

• counts all the checkbutton’s state changes and stores the result in cnt variable;
• presents the current cnt value and the checkbutton’s state after clicking the Show button.

import tkinter as tk
from tkinter import messagebox
 
 
def count():
    global counter
    counter += 1
 
def show():
    messagebox.showinfo("","counter=" + str(counter) + ",state=" + str(switch.get()))
 
 
window = tk.Tk()
switch = tk.IntVar()
counter = 0
button = tk.Button(window, text="Show", command=show)
button.pack()
checkbutton = tk.Checkbutton(window, text="Tick", variable=switch, command=count)
checkbutton.pack()
window.mainloop()

The next sample shows how the invoke() invocation triggers the checkbutton. Analyze the code.

import tkinter as tk
from tkinter import messagebox
 
 
def count():
    global counter
    counter += 1
 
 
def show():
    messagebox.showinfo("", "counter=" + str(counter) + ",state=" + str(switch.get()))
 
 
window = tk.Tk()
switch = tk.IntVar()
counter = 0
button = tk.Button(window, text="Show", command=show)
button.pack()
checkbutton = tk.Checkbutton(window, text="Tick", variable=switch, command=count)
checkbutton.after(1000, checkbutton.invoke)
checkbutton.pack()
window.mainloop()

The Radiobutton is usable when you group (couple) a number (>1) of these widgets – as only one of them can be mutually selected (checked), it’s a good tool to represent one of many user choices. Assigning the same observable variable to more than one Radiobutton creates a group.

This also means that when two Radiobuttons use different observable variables, they belong to different groups by definition.

rdbutton = Radiobutton(master, option, ...)

Here are some of the Radiobutton’s properties:

Let's start with its properties:

Some of the Radiobutton’s methods are shown here.

Note: there is no toggle() method as a single Radiobutton performs such an operation.

import tkinter as tk
from tkinter import messagebox
 
 
def show():
    messagebox.showinfo("", "radio_1=" + str(radio_1_var.get()) +
                        ",radio_2=" + str(radio_2_var.get()))
 
 
def command_1():
    radio_2_var.set(radio_1_var.get())
 
 
def command_2():
    radio_1_var.set(radio_2_var.get())
 
 
window = tk.Tk()
button = tk.Button(window, text="Show", command=show)
button.pack()
radio_1_var = tk.IntVar()
radio_1_1 = tk.Radiobutton(window, text="pizza", variable=radio_1_var, value=1, command=command_1)
radio_1_1.select()
radio_1_1.pack()
radio_1_2 = tk.Radiobutton(window, text="clams", variable=radio_1_var, value=2, command=command_1)
radio_1_2.pack()
radio_2_var = tk.IntVar()
radio_2_1 = tk.Radiobutton(window, text="FR", variable=radio_2_var, value=2, command=command_2)
radio_2_1.pack()
radio_2_2 = tk.Radiobutton(window, text="IT", variable=radio_2_var, value=1, command=command_2)
radio_2_2.select()
radio_2_2.pack()
window.mainloop()

The program defines two separate Radiobutton groups, consisting of two Radiobuttons. These groups are coupled, as their callbacks change the opposite group to reflect the state of their own group. Thanks to that, you can choose a meal and change country, or you can change country and the meal will select itself automatically.

Let’s say “Goodbye” now – we’ll meet again soon to discuss some non-clickable widgets!