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<title>16.1.6.7 Bindings and Events
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16.1.6.7 Bindings and Events
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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:
<div class=
"verbatim"><pre>
def bind(self, sequence, func, add=''):
<DT><STRONG>sequence
</STRONG></DT>
<DD>is a string that denotes the target kind of event. (See the bind
man page and page
201 of John Ousterhout's book for details).
<DT><STRONG>func
</STRONG></DT>
<DD>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
<var>callbacks
</var>.)
<DT><STRONG>add
</STRONG></DT>
<DD>is optional, either
"<tt class="samp
"></tt>" or
"<tt class="samp
">+</tt>". Passing an empty string
denotes that this binding is to replace any other bindings that this
event is associated with. Preceeding with a
"<tt class="samp
">+</tt>" means that this
function is to be added to the list of functions bound to this event type.
<div class=
"verbatim"><pre>
def turnRed(self, event):
event.widget[
"activeforeground"] =
"red"
self.button.bind(
"<Enter>", self.turnRed)
Notice how the widget field of the event is being accessed in the
<tt class=
"method">turnRed()
</tt> 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.
<div class=
"verbatim"><pre>
Tk Tkinter Event Field Tk Tkinter Event Field
-- ------------------- -- -------------------
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