Decorator Recipe: Event Binding in Tkinter

Step 3

The “command” callback for the Button class is a special case of event handling in Tkinter. All other event handling goes through the Widget.bind method, which is used like this:

def onselect(evt):
    # Note here that Tkinter passes an event object to onselect()
    w = evt.widget
    index = int(w.curselection()[0])
    value = w.get(index)
    print 'You selected item %d: "%s"' % (index, value)

lb = Listbox(frame, name='lb')
lb.bind('<<ListboxSelect>>', onselect)

Create a decorator function called bind, which accepts two arguments: the first argument is a widget object, the second is an event descriptor string (e.g. ‘<<ListboxSelect>>’).

from Tkinter import *

def bind(widget, event):
    """Write the body of this function"""

if __name__ == '__main__':
    frame = Frame()
    frame.master.title("Event binding with decorators")
    frame.pack()

    lb = Listbox(frame, name='lb')
    for s in ['One', 'Two', 'Three', 'Four']:
        lb.insert(END, s)
    lb.pack()

    @bind(lb, '<<ListboxSelect>>')
    def onselect(evt):
        w = evt.widget
        index = int(w.curselection()[0])
        value = w.get(index)
        print 'You selected item %d: "%s"' % (index, value)

    frame.mainloop()

Expected output:

Hints

1. The bind function needs to return a function.
2. The function returned by bind also returns a function.
3. The function returned by bind is a decorator.
4. You will need to use a closure.
5. Your solution might contain the following statement: widget.bind(event, func).

Solution: solutions/tkinter3.py

Go back