Programming Python, Second Edition

Checkbutton, Radiobutton, and Scale

This section introduces three widget types -- the Checkbutton (a multiple-choice input widget), the Radionbutton (a single-choice device), and the Scale (sometimes known as a “slider”). All are variations on a theme, and somewhat related to simple buttons, so we’ll explore them as a group here. To make these widgets more fun to play with, we’ll reuse the dialogTable module shown in Example 7-8 to provide callbacks for widget selections (callbacks pop up dialog boxes). Along the way, we’ll also use the Tkinter variables we just met to communicate with these widgets’ state settings.

Checkbuttons

The Checkbutton and Radiobutton widgets are designed to be associated with Tkinter variables: pushing the button changes the value of the variable, and setting the variable changes the state of the button it is linked to. In fact, Tkinter variables are central to the operation of these widgets:

• A collection of checkbuttons implements a multiple-choice interface, by assigning each button a variable of its own.

• A collection of radiobuttons imposes a mutually exclusive single-choice model, by giving each button a unique value and the same Tkinter variable.

Both kinds of buttons provide both command and variable options. The command option lets you register a callback to be run immediately on button-press events, much like normal Button widgets. But by associating a Tkinter variable with the variable option, you can also fetch or change widget state at any ...