-
Notifications
You must be signed in to change notification settings - Fork 1
Expand file tree
/
Copy pathpython-xlib_10.html
More file actions
161 lines (144 loc) · 7.14 KB
/
python-xlib_10.html
File metadata and controls
161 lines (144 loc) · 7.14 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Created on September 16, 2020 by texi2html 5.0
texi2html was written by:
Lionel Cons <Lionel.Cons@cern.ch> (original author)
Karl Berry <karl@freefriends.org>
Olaf Bachmann <obachman@mathematik.uni-kl.de>
and many others.
Maintained by: Many creative people.
Send bugs and suggestions to <texi2html-bug@nongnu.org>
-->
<head>
<title>The Python X Library: 5.1 Getting Events</title>
<meta name="description" content="The Python X Library: 5.1 Getting Events">
<meta name="keywords" content="The Python X Library: 5.1 Getting Events">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="texi2html 5.0">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
pre.display {font-family: serif}
pre.format {font-family: serif}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: serif; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: serif; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:pre}
span.nolinebreak {white-space:pre}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>
</head>
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Getting-Events"></a>
<table class="header" cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Beginning of this chapter or previous chapter"> << </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Previous section in reading order"> < </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Up section"> Up </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_11.html#Selecting-Events" title="Next section in reading order"> > </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_14.html#X-Objects" title="Next chapter"> >> </a>]</td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left">[<a href="python-xlib.html#Top" title="Cover (top) of document">Top</a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
<td valign="middle" align="left">[Index]</td>
<td valign="middle" align="left">[<a href="python-xlib_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<hr>
<a name="Getting-Events-1"></a>
<h2 class="section">5.1 Getting Events</h2>
<p>Events can be sent at any time, not necessarily when the client is ready
to receive an event. Therefore they must be stored temporarily from that
they are read from the network until the client is ready to handle them.
Read but unhandled events are stored on an event queue in the Display
object. There are two functions to access this queue:
</p>
<dl>
<dt><a name="index-next_005fevent-on-Display"></a>Method on Display: <strong>next_event</strong><em> ( )</em></dt>
<dd>
<p>Return the next event in the event queue. If the event queue is empty,
block until an event is read from the network, and return that one.
</p>
</dd></dl>
<dl>
<dt><a name="index-pending_005fevents-on-Display"></a>Method on Display: <strong>pending_events</strong><em> ( )</em></dt>
<dd>
<p>Return the number of events which can be returned without blocking.
</p>
</dd></dl>
<p>A trivial event loop would simply loop infinitely, waiting for an
event and then handling it. It could look like this:
</p>
<div class="example">
<pre class="example">while 1:
event = disp.next_event()
handle_event(event)
</pre></div>
<p>However, most applications need more control, e.g. to simultaneously
handle a network connection or at regular intervals schedule timeouts.
The module <code>select</code> is often used for this. <code>Display</code> objects
can be used with <code>select</code>, since they have the required
<code>fileno()</code> method. When <code>select</code> indicates that a
<code>Display</code> object is ready for reading, that means that the server
has sent some data to the client. That alone doesn’t guarantee that an
entire event has arrived, so one must first use <code>pending_events()</code>
to make sure that <code>next_event()</code> will return without blocking. A
simple event loop which waits for events or a one-second timeout looks
like this:
</p>
<div class="example">
<pre class="example">while 1:
# Wait for display to send something, or a timeout of one second
readable, w, e = select.select([disp], [], [], 1)
# if no files are ready to be read, it's an timeout
if not readable:
handle_timeout()
# if display is readable, handle as many events as have been received
elif disp in readable:
i = disp.pending_events()
while i > 0:
event = disp.next_event()
handle_event(event)
i = i - 1
# loop around to wait for more things to happen
</pre></div>
<hr>
<table class="header" cellpadding="1" cellspacing="1" border="0">
<tr><td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Beginning of this chapter or previous chapter"> << </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Previous section in reading order"> < </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_9.html#Event-Handling" title="Up section"> Up </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_11.html#Selecting-Events" title="Next section in reading order"> > </a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_14.html#X-Objects" title="Next chapter"> >> </a>]</td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left"> </td>
<td valign="middle" align="left">[<a href="python-xlib.html#Top" title="Cover (top) of document">Top</a>]</td>
<td valign="middle" align="left">[<a href="python-xlib_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
<td valign="middle" align="left">[Index]</td>
<td valign="middle" align="left">[<a href="python-xlib_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
</tr></table>
<p>
<font size="-1">
This document was generated on <i>September 16, 2020</i> using <a href="http://www.nongnu.org/texi2html/"><i>texi2html 5.0</i></a>.
</font>
<br>
</p>
</body>
</html>