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55 | <H3><A NAME="SECTION0018167000000000000000"> | |
56 | 16.1.6.7 Bindings and Events</A> | |
57 | </H3> | |
58 | <P> | |
59 | <a id='l2h-4840' xml:id='l2h-4840'></a> | |
60 | ||
61 | <P> | |
62 | The bind method from the widget command allows you to watch for | |
63 | certain events and to have a callback function trigger when that event | |
64 | type occurs. The form of the bind method is: | |
65 | ||
66 | <P> | |
67 | <div class="verbatim"><pre> | |
68 | def bind(self, sequence, func, add=''): | |
69 | </pre></div> | |
70 | where: | |
71 | ||
72 | <P> | |
73 | <DL> | |
74 | <DT><STRONG>sequence</STRONG></DT> | |
75 | <DD>is a string that denotes the target kind of event. (See the bind | |
76 | man page and page 201 of John Ousterhout's book for details). | |
77 | ||
78 | <P> | |
79 | </DD> | |
80 | <DT><STRONG>func</STRONG></DT> | |
81 | <DD>is a Python function, taking one argument, to be invoked when the | |
82 | event occurs. An Event instance will be passed as the argument. | |
83 | (Functions deployed this way are commonly known as <var>callbacks</var>.) | |
84 | ||
85 | <P> | |
86 | </DD> | |
87 | <DT><STRONG>add</STRONG></DT> | |
88 | <DD>is optional, either "<tt class="samp"></tt>" or "<tt class="samp">+</tt>". Passing an empty string | |
89 | denotes that this binding is to replace any other bindings that this | |
90 | event is associated with. Preceeding with a "<tt class="samp">+</tt>" means that this | |
91 | function is to be added to the list of functions bound to this event type. | |
92 | </DD> | |
93 | </DL> | |
94 | ||
95 | <P> | |
96 | For example: | |
97 | <div class="verbatim"><pre> | |
98 | def turnRed(self, event): | |
99 | event.widget["activeforeground"] = "red" | |
100 | ||
101 | self.button.bind("<Enter>", self.turnRed) | |
102 | </pre></div> | |
103 | ||
104 | <P> | |
105 | Notice how the widget field of the event is being accessed in the | |
106 | <tt class="method">turnRed()</tt> callback. This field contains the widget that | |
107 | caught the X event. The following table lists the other event fields | |
108 | you can access, and how they are denoted in Tk, which can be useful | |
109 | when referring to the Tk man pages. | |
110 | ||
111 | <P> | |
112 | <div class="verbatim"><pre> | |
113 | Tk Tkinter Event Field Tk Tkinter Event Field | |
114 | -- ------------------- -- ------------------- | |
115 | %f focus %A char | |
116 | %h height %E send_event | |
117 | %k keycode %K keysym | |
118 | %s state %N keysym_num | |
119 | %t time %T type | |
120 | %w width %W widget | |
121 | %x x %X x_root | |
122 | %y y %Y y_root | |
123 | </pre></div> | |
124 | ||
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