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<H1><A NAME="SECTION007400000000000000000">
5.4 <tt class="module">whrandom</tt> --
Pseudo-random number generator</A>
</H1>
<P>
<P>
This module implements a Wichmann-Hill pseudo-random number generator
class that is also named <tt class="class">whrandom</tt>. Instances of the
<tt class="class">whrandom</tt> class conform to the Random Number Generator
interface described in section <A href="rng-objects.html#rng-objects" tppabs="http://www.python.org/doc/current/lib/rng-objects.html#rng-objects">5.3.1</A>. They also offer the
following method, specific to the Wichmann-Hill algorithm:
<P>
<dl><dt><b><a name='l2h-747'><tt class='method'>seed</tt></a></b> (<big>[</big><var>x, y, z</var><big>]</big>)
<dd>
Initializes the random number generator from the integers <var>x</var>,
<var>y</var> and <var>z</var>. When the module is first imported, the random
number is initialized using values derived from the current time.
If <var>x</var>, <var>y</var>, and <var>z</var> are either omitted or <code>0</code>, the
seed will be computed from the current system time. If one or two
of the parameters are <code>0</code>, but not all three, the zero values
are replaced by ones. This causes some apparently different seeds
to be equal, with the corresponding result on the pseudo-random
series produced by the generator.
</dl>
<P>
<dl><dt><b><a name='l2h-748'><tt class='function'>choice</tt></a></b> (<var>seq</var>)
<dd>
Chooses a random element from the non-empty sequence <var>seq</var> and returns it.
</dl>
<P>
<dl><dt><b><a name='l2h-749'><tt class='function'>randint</tt></a></b> (<var>a, b</var>)
<dd>
Returns a random integer <var>N</var> such that <code><var>a</var><=<var>N</var><=<var>b</var></code>.
</dl>
<P>
<dl><dt><b><a name='l2h-750'><tt class='function'>random</tt></a></b> ()
<dd>
Returns the next random floating point number in the range [0.0 ... 1.0).
</dl>
<P>
<dl><dt><b><a name='l2h-751'><tt class='function'>seed</tt></a></b> (<var>x, y, z</var>)
<dd>
Initializes the random number generator from the integers <var>x</var>,
<var>y</var> and <var>z</var>. When the module is first imported, the random
number is initialized using values derived from the current time.
</dl>
<P>
<dl><dt><b><a name='l2h-752'><tt class='function'>uniform</tt></a></b> (<var>a, b</var>)
<dd>
Returns a random real number <var>N</var> such that <code><var>a</var><=<var>N</var><<var>b</var></code>.
</dl>
<P>
When imported, the <tt class="module">whrandom</tt> module also creates an instance of
the <tt class="class">whrandom</tt> class, and makes the methods of that instance
available at the module level. Therefore one can write either
<code>N = whrandom.random()</code> or:
<P>
<dl><dd><pre class="verbatim">
generator = whrandom.whrandom()
N = generator.random()
</pre></dl>
<P>
Note that using separate instances of the generator leads to
independent sequences of pseudo-random numbers.
<P>
<div class='seealso'>
<p class='heading'><b>See Also:</b></p>
<dl compact class="seemodule">
<dt>Module <b><tt class='module'><a href="module-random.html" tppabs="http://www.python.org/doc/current/lib/module-random.html">random</a></tt>:</b>
<dd>Generators for various random distributions and
documentation for the Random Number Generator
interface.
</dl>
<div class="seetext"><p>Wichmann, B. A. & Hill, I. D., ``Algorithm AS 183:
An efficient and portable pseudo-random number generator'',
<em class='citetitle'
>Applied Statistics</em> 31 (1982) 188-190.</div>
</div>
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