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| 17 | <title>5.10 whrandom -- Pseudo-random number generator</title> | |
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| 54 | ||
| 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> | |
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