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Initial commit of OpenSPARC T2 architecture model.
[OpenSPARC-T2-SAM] / sam-t2 / devtools / v9 / html / python / lib / module-timeit.html
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16<title>10.10 timeit -- Measure execution time of small code snippets</title>
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54<H1><A NAME="SECTION00121000000000000000000">
5510.10 <tt class="module">timeit</tt> --
56 Measure execution time of small code snippets</A>
57</H1>
58
59<P>
60<A NAME="module-timeit"></A>
61
62<P>
63
64<span class="versionnote">New in version 2.3.</span>
65
66<a id='l2h-3138' xml:id='l2h-3138'></a>
67
68<P>
69This module provides a simple way to time small bits of Python code.
70It has both command line as well as callable interfaces. It avoids a
71number of common traps for measuring execution times. See also Tim
72Peters' introduction to the ``Algorithms'' chapter in the
73<em class="citetitle"
74 >Python Cookbook</em>, published by O'Reilly.
75
76<P>
77The module defines the following public class:
78
79<P>
80<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
81 <td><nobr><b><span class="typelabel">class</span>&nbsp;<tt id='l2h-3134' xml:id='l2h-3134' class="class">Timer</tt></b>(</nobr></td>
82 <td><var></var><big>[</big><var>stmt=<code>'pass'</code>
83 </var><big>[</big><var>, setup=<code>'pass'</code>
84 </var><big>[</big><var>, timer=&lt;timer function&gt;</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
85<dd>
86Class for timing execution speed of small code snippets.
87
88<P>
89The constructor takes a statement to be timed, an additional statement
90used for setup, and a timer function. Both statements default to
91<code>'pass'</code>; the timer function is platform-dependent (see the
92module doc string). The statements may contain newlines, as long as
93they don't contain multi-line string literals.
94
95<P>
96To measure the execution time of the first statement, use the
97<tt class="method">timeit()</tt> method. The <tt class="method">repeat()</tt> method is a
98convenience to call <tt class="method">timeit()</tt> multiple times and return a list
99of results.
100</dl>
101
102<P>
103<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
104 <td><nobr><b><tt id='l2h-3135' xml:id='l2h-3135' class="method">print_exc</tt></b>(</nobr></td>
105 <td><var></var><big>[</big><var>file=<tt class="constant">None</tt></var><big>]</big><var></var>)</td></tr></table></dt>
106<dd>
107Helper to print a traceback from the timed code.
108
109<P>
110Typical use:
111
112<P>
113<div class="verbatim"><pre>
114 t = Timer(...) # outside the try/except
115 try:
116 t.timeit(...) # or t.repeat(...)
117 except:
118 t.print_exc()
119</pre></div>
120
121<P>
122The advantage over the standard traceback is that source lines in the
123compiled template will be displayed.
124The optional <var>file</var> argument directs where the traceback is sent;
125it defaults to <code>sys.stderr</code>.
126</dl>
127
128<P>
129<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
130 <td><nobr><b><tt id='l2h-3136' xml:id='l2h-3136' class="method">repeat</tt></b>(</nobr></td>
131 <td><var></var><big>[</big><var>repeat<code>=3</code> </var><big>[</big><var>,
132 number<code>=1000000</code></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
133<dd>
134Call <tt class="method">timeit()</tt> a few times.
135
136<P>
137This is a convenience function that calls the <tt class="method">timeit()</tt>
138repeatedly, returning a list of results. The first argument specifies
139how many times to call <tt class="method">timeit()</tt>. The second argument
140specifies the <var>number</var> argument for <tt class="function">timeit()</tt>.
141
142<P>
143<div class="note"><b class="label">Note:</b>
144It's tempting to calculate mean and standard deviation from the result
145vector and report these. However, this is not very useful. In a typical
146case, the lowest value gives a lower bound for how fast your machine can run
147the given code snippet; higher values in the result vector are typically not
148caused by variability in Python's speed, but by other processes interfering
149with your timing accuracy. So the <tt class="function">min()</tt> of the result is
150probably the only number you should be interested in. After that, you
151should look at the entire vector and apply common sense rather than
152statistics.
153</div>
154</dl>
155
156<P>
157<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
158 <td><nobr><b><tt id='l2h-3137' xml:id='l2h-3137' class="method">timeit</tt></b>(</nobr></td>
159 <td><var></var><big>[</big><var>number<code>=1000000</code></var><big>]</big><var></var>)</td></tr></table></dt>
160<dd>
161Time <var>number</var> executions of the main statement.
162This executes the setup statement once, and then
163returns the time it takes to execute the main statement a number of
164times, measured in seconds as a float. The argument is the number of
165times through the loop, defaulting to one million. The main
166statement, the setup statement and the timer function to be used are
167passed to the constructor.
168
169<P>
170<div class="note"><b class="label">Note:</b>
171By default, <tt class="method">timeit()</tt> temporarily turns off garbage collection
172during the timing. The advantage of this approach is that it makes
173independent timings more comparable. This disadvantage is that GC
174may be an important component of the performance of the function being
175measured. If so, GC can be re-enabled as the first statement in the
176<var>setup</var> string. For example:
177<div class="verbatim"><pre>
178 timeit.Timer('for i in xrange(10): oct(i)', 'gc.enable()').timeit()
179</pre></div>
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181</dl>
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231<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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