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copied!<p>As per comments, I've updated the code:</p> <pre><code>import time import math def timeit1(): s = time.time() for i in xrange(750000): z=i**.5 print "Took %f seconds" % (time.time() - s) def timeit2(arg=math.sqrt): s = time.time() for i in xrange(750000): z=arg(i) print "Took %f seconds" % (time.time() - s) timeit1() timeit2() </code></pre> <p>Now the <code>math.sqrt</code> function is directly in a local argument, meaning it has the fastest lookup possible. </p> <p><strong>UPDATE:</strong> The python version seems to matter here. I used to think that <code>timeit1</code> would be faster, since when python parses "i**.5" it knows, syntactically, which method to call (<code>__pow__</code> or some variant), so it doesn't have to go through the overhead of lookup that the <code>math.sqrt</code> variant does. But I might be wrong:</p> <p><strong>Python 2.5:</strong> 0.191000 vs. 0.224000</p> <p><strong>Python 2.6:</strong> 0.195000 vs. 0.139000</p> <p>Also psyco seems to deal with <code>math.sqrt</code> better:</p> <p><strong>Python 2.5 + Psyco 2.0:</strong> 0.109000 vs. 0.043000</p> <p><strong>Python 2.6 + Psyco 2.0:</strong> 0.128000 vs. 0.067000</p> <hr> <pre><code>| Interpreter | x**.5, | sqrt, | sqrt faster, % | | | seconds | seconds | | |----------------+---------+---------+----------------| | Python 3.2rc1+ | 0.32 | 0.27 | 19 | | Python 3.1.2 | 0.136 | 0.088 | 55 | | Python 3.0.1 | 0.155 | 0.102 | 52 | | Python 2.7 | 0.132 | 0.079 | 67 | | Python 2.6.6 | 0.121 | 0.075 | 61 | | PyPy 1.4.1 | 0.083 | 0.0159 | 422 | | Jython 2.5.1 | 0.132 | 0.22 | -40 | | Python 2.5.5 | 0.129 | 0.125 | 3 | | Python 2.4.6 | 0.131 | 0.123 | 7 | #+TBLFM: $4=100*($2-$3)/$3;%.0f </code></pre> <p>Table results produced on machine:</p> <pre><code>$ uname -vms Linux #42-Ubuntu SMP Thu Dec 2 02:41:37 UTC 2010 x86_64 $ cat /proc/cpuinfo | grep 'model name' | head -1 model name : Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz </code></pre> <p>To reproduce results:</p> <ul> <li>get source: <a href="https://gist.github.com/783011" rel="noreferrer"><code>git clone git://gist.github.com/783011.git gist-783011</code></a></li> <li>install <a href="http://codespeak.net/tox/" rel="noreferrer"><code>tox</code></a>: <code>pip install tox</code></li> <li>run <code>tox</code> from the directory with <code>tox.ini</code> file.</li> </ul>

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