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17 | <title>5.10 whrandom -- Pseudo-random number generator</title> | |
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55 | <H1><A NAME="SECTION0071000000000000000000"> | |
56 | 5.10 <tt class="module">whrandom</tt> -- | |
57 | Pseudo-random number generator</A> | |
58 | </H1> | |
59 | ||
60 | <P> | |
61 | <A NAME="module-whrandom"></A> | |
62 | ||
63 | <P> | |
64 | <div class="versionnote"><b>Deprecated since release 2.1.</b> | |
65 | Use <tt class="module"><a href="module-random.html">random</a></tt> instead.</div><p></p> | |
66 | ||
67 | <P> | |
68 | <span class="note"><b class="label">Note:</b> | |
69 | This module was an implementation detail of the | |
70 | <tt class="module"><a href="module-random.html">random</a></tt> module in releases of Python prior to 2.1. It is | |
71 | no longer used. Please do not use this module directly; use | |
72 | <tt class="module"><a href="module-random.html">random</a></tt> instead.</span> | |
73 | ||
74 | <P> | |
75 | This module implements a Wichmann-Hill pseudo-random number generator | |
76 | class that is also named <tt class="class">whrandom</tt>. Instances of the | |
77 | <tt class="class">whrandom</tt> class conform to the Random Number Generator | |
78 | interface described in the docs for the <tt class="module"><a href="module-random.html">random</a></tt> module. | |
79 | They also offer the | |
80 | following method, specific to the Wichmann-Hill algorithm: | |
81 | ||
82 | <P> | |
83 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
84 | <td><nobr><b><tt id='l2h-1323' xml:id='l2h-1323' class="method">seed</tt></b>(</nobr></td> | |
85 | <td><var></var><big>[</big><var>x, y, z</var><big>]</big><var></var>)</td></tr></table></dt> | |
86 | <dd> | |
87 | Initializes the random number generator from the integers <var>x</var>, | |
88 | <var>y</var> and <var>z</var>. When the module is first imported, the random | |
89 | number is initialized using values derived from the current time. | |
90 | If <var>x</var>, <var>y</var>, and <var>z</var> are either omitted or <code>0</code>, the | |
91 | seed will be computed from the current system time. If one or two | |
92 | of the parameters are <code>0</code>, but not all three, the zero values | |
93 | are replaced by ones. This causes some apparently different seeds | |
94 | to be equal, with the corresponding result on the pseudo-random | |
95 | series produced by the generator. | |
96 | </dl> | |
97 | ||
98 | <P> | |
99 | Other supported methods include: | |
100 | ||
101 | <P> | |
102 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
103 | <td><nobr><b><tt id='l2h-1324' xml:id='l2h-1324' class="function">choice</tt></b>(</nobr></td> | |
104 | <td><var>seq</var>)</td></tr></table></dt> | |
105 | <dd> | |
106 | Chooses a random element from the non-empty sequence <var>seq</var> and returns it. | |
107 | </dl> | |
108 | ||
109 | <P> | |
110 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
111 | <td><nobr><b><tt id='l2h-1325' xml:id='l2h-1325' class="function">randint</tt></b>(</nobr></td> | |
112 | <td><var>a, b</var>)</td></tr></table></dt> | |
113 | <dd> | |
114 | Returns a random integer <var>N</var> such that <code><var>a</var><=<var>N</var><=<var>b</var></code>. | |
115 | </dl> | |
116 | ||
117 | <P> | |
118 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
119 | <td><nobr><b><tt id='l2h-1326' xml:id='l2h-1326' class="function">random</tt></b>(</nobr></td> | |
120 | <td><var></var>)</td></tr></table></dt> | |
121 | <dd> | |
122 | Returns the next random floating point number in the range [0.0 ... 1.0). | |
123 | </dl> | |
124 | ||
125 | <P> | |
126 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
127 | <td><nobr><b><tt id='l2h-1327' xml:id='l2h-1327' class="function">seed</tt></b>(</nobr></td> | |
128 | <td><var>x, y, z</var>)</td></tr></table></dt> | |
129 | <dd> | |
130 | Initializes the random number generator from the integers <var>x</var>, | |
131 | <var>y</var> and <var>z</var>. When the module is first imported, the random | |
132 | number is initialized using values derived from the current time. | |
133 | </dl> | |
134 | ||
135 | <P> | |
136 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
137 | <td><nobr><b><tt id='l2h-1328' xml:id='l2h-1328' class="function">uniform</tt></b>(</nobr></td> | |
138 | <td><var>a, b</var>)</td></tr></table></dt> | |
139 | <dd> | |
140 | Returns a random real number <var>N</var> such that <code><var>a</var><=<var>N</var><<var>b</var></code>. | |
141 | </dl> | |
142 | ||
143 | <P> | |
144 | When imported, the <tt class="module">whrandom</tt> module also creates an instance of | |
145 | the <tt class="class">whrandom</tt> class, and makes the methods of that instance | |
146 | available at the module level. Therefore one can write either | |
147 | <code>N = whrandom.random()</code> or: | |
148 | ||
149 | <P> | |
150 | <div class="verbatim"><pre> | |
151 | generator = whrandom.whrandom() | |
152 | N = generator.random() | |
153 | </pre></div> | |
154 | ||
155 | <P> | |
156 | Note that using separate instances of the generator leads to | |
157 | independent sequences of pseudo-random numbers. | |
158 | ||
159 | <P> | |
160 | <div class="seealso"> | |
161 | <p class="heading">See Also:</p> | |
162 | ||
163 | <dl compact="compact" class="seemodule"> | |
164 | <dt>Module <b><tt class="module"><a href="module-random.html">random</a></tt>:</b> | |
165 | <dd>Generators for various random distributions and | |
166 | documentation for the Random Number Generator | |
167 | interface. | |
168 | </dl> | |
169 | <div class="seetext"><p>Wichmann, B. A. & Hill, I. D., ``Algorithm AS 183: | |
170 | An efficient and portable pseudo-random number generator'', | |
171 | <em class="citetitle" | |
172 | >Applied Statistics</em> 31 (1982) 188-190.</p></div> | |
173 | </div> | |
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