Being able to react to events is one of the most basic but important topics in GUI application development since it determines how users can interact with the program.

Pressing keys of the keyboard and clicking on items with the mouse are some common types of events, which are automatically handled in some Tkinter classes. For instance, this behavior is already implemented on the command option of the Button widget class, which invokes the specified callback function.

Some events can get triggered without user interaction, such as changing the input focus programmatically from one widget to another.