Checkbutton¶

A checkbutton is like a regular button, with a label and a callback function, but it also holds and displays a binary state.

The Checkbutton object has the following attributes:

parent - the parent object
text - the label to display
command - the callback function
variable - the variable holding the state value
onvalue - the value when in the ON state
offvalue - the value when in the OFF state

The standard checkbutton¶

Here is an example of 3 checkbuttons

The callback function cb writes this to the console:

--- languages ---
English 1
German 0
French fluent

We notice that the default offvalue is 0 and the default onvalue is 1. In our case:

var0 toggles between 0 and 1
var1 toggles between barely and 1
var2 toggles between 0 and fluent

import tkinter as tk

root = tk.Tk()

var0 = tk.StringVar(value='1')
var1 = tk.StringVar(value='0')
var2 = tk.StringVar(value='0')

def cb():
    print('--- languages ---')
    print('English', var0.get())
    print('German', var1.get())
    print('French', var2.get())

tk.Checkbutton(root, text='English', variable=var0, command=cb).pack()
tk.Checkbutton(root, text='German', variable=var1, offvalue='barely', command=cb).pack()
tk.Checkbutton(root, text='French', variable=var2, onvalue='fluent', command=cb).pack()

root.mainloop()

check1.py

Now let us rewrite this program by using lists.

import tkinter as tk

root = tk.Tk()

texts = ['English', 'German', 'French']
vars = [tk.StringVar(value='0'), tk.StringVar(value='0'), tk.StringVar(value='0')]

def cb():
    print('--- languages ---')
    for i, s in enumerate(texts):
        print(s, vars[i].get())

tk.Checkbutton(root, text=texts[0], variable=vars[0], command=cb).pack()
tk.Checkbutton(root, text=texts[1], variable=vars[1], command=cb).pack()
tk.Checkbutton(root, text=texts[2], variable=vars[2], command=cb).pack()

root.mainloop()

check2.py

A better Checkbutton class¶

It’s time now to define a new and better Checkbutton class which can do everything in one line:

Checkbutton('English;German;French', 'print(self.selection)')

the items are declared as a semicolon-separated list
the command is a string to be evaluated in the Checkbutton environment
the items are available in self.items
the selected items are available in self.selection
the selection states are available in self.val

This is the result written to the console for three consecutive selections:

['French']
['German', 'French']
['English', 'German', 'French']

"""Create checkbuttons."""
from tklib import *

app = App()
Checkbutton('English;German;French', 'print(self.selection)')
app.run()

check3.py

Now let’s see how this class is defined