# tkinter --- Python interface to Tcl/Tk — Bindings and events

> single: bind (widgets) single: events (widgets) The bind method from the widget command allows you to watch for certain events and to have a callback function trigger when that event type occurs.

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single: bind (widgets) single: events (widgets)

The bind method from the widget command allows you to watch for certain events and to have a callback function trigger when that event type occurs. The form of the bind method is

def bind(self, sequence, func, add='')

sequence is a string that denotes the target kind of event. Physical events use the form (for example "" or ""); application-defined virtual events use double angle brackets, as in "&gt;". (See the bind(3tk) man page for details.)

func is a Python function, taking one argument, to be invoked when the event occurs. An Event instance will be passed as the argument. (Functions deployed this way are commonly known as callbacks.)

add is optional, either '' or '+'. Passing an empty string denotes that this binding is to replace any other bindings that this event is associated with. Passing a '+' means that this function is to be added to the list of functions bound to this event type.

def turn_red(self, event): event.widget["activeforeground"] = "red"

self.button.bind("", self.turn_red)

Notice how the widget field of the event is being accessed in the turn_red() callback. This field contains the widget that caught the X event. The following table lists the other event fields you can access, and how they are denoted in Tk, which can be useful when referring to the Tk man pages.

The add parameter above only affects the bindings you make yourself. Every widget also inherits class bindings that implement its standard behavior -- for example a Text widget binds Control-t to transpose two characters. These are described in the bindings section of the widget's Tk man page (such as text(3tk) or entry(3tk)).

Class bindings are processed separately from your own, so binding an event yourself does not replace the default; both run. To suppress an unwanted default binding, bind the event on the widget and return the string "break" from your callback.

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