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<TITLE> Description of Objects in VPython</TITLE>
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<H1 CLASS="Heading-1"> <font color="#0000A0">Keyboard Interactions</font></H1>
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<P CLASS="Normal">If<span class="attribute"> scene.kb.keys</span> is nonzero,
one or more keyboard events have been stored, waiting to be processed.</P>
<P CLASS="Normal">Executing <span class="attribute">key</span> <span class="attribute">=</span>
<span class="attribute">scene.kb.getkey()</span> obtains a keyboard input
and removes it from the input queue. If there are no events waiting to be
processed, getkey() waits until a key is pressed.</P>
<P CLASS="Normal">If len(key) == 1, the input is a single printable character
such as 'b' or 'B' or new line ('\n') or tab ('\t'). Otherwise key is a multicharacter
string such as 'escape' or 'backspace' or 'f3'. For such inputs, the ctrl,
alt, and shift keys are prepended to the key name. For example, if you hold
down the shift key and press F3, key will be the character string 'shift+f3',
which you can test for explicitly. If you hold down all three modifier keys,
you get 'ctrl+alt+shift+f3'; the order is always ctrl, alt, shift.</P>
<P CLASS="Normal">Here is a test routine that let's you type text into a label:</P>
<P CLASS="Normal"> </P>
<p class="program"><span class="program">prose = label() # initially blank text</span></p>
<p class="program">while 1: </p>
<p class="program"> if scene.kb.keys: # is there an event
waiting to be processed?</p>
<p class="program"> <span class="program">s
= scene.kb.getkey() # obtain keyboard information</span></p>
<p class="program"> <span class="program">if
len(s) == 1:</span> </p>
<p class="program"> <span class="program">prose.text
+= s # append new character</span></p>
<p class="program"> <span class="program">elif
(s == 'backspace' or s == 'delete') and len(prose.text) > 0: </span> </p>
<p class="program"> <span class="program">prose.text
= prose.text[:-1] # erase one letter</span></p>
<p class="program"> <span class="program">elif
s == 'shift+delete':</span> </p>
<p class="program"> <span class="program">prose.text
= '' # erase all the text</span></p>
<p class="program"> </p>
<P CLASS="Normal">Note that <a href="mouse.html">mouse events</a> also provide
information about the ctrl, alt, and shift keys, which may be used to modify
mouse actions.</P>
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