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
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"><HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">
<META NAME="GENERATOR" CONTENT="Adobe FrameMaker 5.5/HTML Export Filter">
<LINK REL="STYLESHEET" HREF="VisualRef.css" CHARSET="ISO-8859-1" TYPE="text/css">
<TITLE> Description of Objects in VPython</TITLE>
</HEAD>
<BODY BGCOLOR="#ffffff">
<DIV CLASS="navigation"><table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A HREF="rate.html"><img src="icons/previous.gif" border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="index.html"><img src="icons/up.gif" border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="vector.html"><img src="icons/next.gif" border="0" height="32"
alt="Next Page" width="32"></A></td>
<td align="center" width="100%">Visual Reference</td>
<td><A HREF="index.html"><img src="icons/contents.gif" border="0" height="32"
alt="Contents" width="32"></A></td>
<td><img src="icons/blank.gif" border="0" height="32"
alt="" width="32"></td>
<td><img src="icons/blank.gif" border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="rate.html">Limiting
the Animation Rate</A> <b class="navlabel">Up:</b> <a class="sectref" HREF="index.html">Contents</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="vector.html">The vector
Object</A> <br>
<hr>
</DIV>
<DIV>
<H1 CLASS="Heading-1"> <font color="#0000A0">Floating Division</font></H1>
</DIV>
<DIV>
<P CLASS="Normal"> By default, Python performs integer division with truncation,
so that 3/4 is 0, not 0.75. This is inconvenient when doing scientific computations,
and can lead to hard-to-find bugs in programs. You can write 3./4., which
is 0.75 by the rules of "floating-point" division. </P>
<P CLASS="Normal">Starting with Python 2.2, you can change the default so that
3/4 is treated as 0.75. Place this at the start of your program:</P>
<P CLASS="Normal"><br>
</P>
<P CLASS="program">from __future__ import division</P>
<P CLASS="Normal"> </P>
<P CLASS="Normal">There are two underscores ("_" and "_")
before "future" and two after. </P>
<P CLASS="Normal">The Visual module converts integers to floating-point numbers
for you when specifying attributes of objects:</P>
<DIV>
<P CLASS="Normal"> <span class="attribute"> object.pos
= (1,2,3)</span> is equivalent to <span class="attribute">object.pos = (1.,2.,3.)
</span></P>
<p CLASS="Normal">A related issue in versions of Python preceding Python 2.2
is that raising an integer to a negative power, as in 10**-2, gives an error.
Instead, use 10. (a floating-point number) and write the expression as 10.**-2
in order to obtain the desired result (0.01 in this case). This is not a
problem in Python 2.2 and later versions.</p>
</DIV>
</DIV>
<br><hr>
<DIV CLASS="navigation"><table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A HREF="rate.html"><img src="icons/previous.gif" border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="index.html"><img src="icons/up.gif" border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="vector.html"><img src="icons/next.gif" border="0" height="32"
alt="Next Page" width="32"></A></td>
<td align="center" width="100%">Visual Reference</td>
<td><A HREF="index.html"><img src="icons/contents.gif" border="0" height="32"
alt="Contents" width="32"></A></td>
<td><img src="icons/blank.gif" border="0" height="32"
alt="" width="32"></td>
<td><img src="icons/blank.gif" border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="rate.html">Limiting
the Animation Rate</A> <b class="navlabel">Up:</b> <a class="sectref" HREF="index.html">Contents</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="vector.html">The vector
Object</A> <br>
<hr>
</DIV>
</BODY>
</HTML>
|
