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Code Editor : timeit.html

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 <section id="module-timeit">
<h1>26.6. <a class="reference internal" href="#module-timeit" title="timeit: Measure the execution time of small code snippets."><code class="xref py py-mod docutils literal notranslate">timeit</code></a> — Measure execution time of small code snippets<a class="headerlink" href="#module-timeit" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 2.3.
</div>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/2.7/Lib/timeit.py">Lib/timeit.py</a>
<hr class="docutils" />
This module provides a simple way to time small bits of Python code. It has both
a <a class="reference internal" href="#timeit-command-line-interface">Command-Line Interface</a> as well as a <a class="reference internal" href="#python-interface">callable</a>
one. It avoids a number of common traps for measuring execution times.
See also Tim Peters’ introduction to the “Algorithms” chapter in the Python
Cookbook, published by O’Reilly.
<section id="basic-examples">
<h2>26.6.1. Basic Examples<a class="headerlink" href="#basic-examples" title="Permalink to this headline">¶</a></h2>
The following example shows how the <a class="reference internal" href="#timeit-command-line-interface">Command-Line Interface</a>
can be used to compare three different expressions:
<div class="highlight-sh notranslate"><div class="highlight"><pre>$ python -m timeit &#39;&quot;-&quot;.join(str(n) for n in range(100))&#39;
10000 loops, best of 3: 40.3 usec per loop
$ python -m timeit &#39;&quot;-&quot;.join([str(n) for n in range(100)])&#39;
10000 loops, best of 3: 33.4 usec per loop
$ python -m timeit &#39;&quot;-&quot;.join(map(str, range(100)))&#39;
10000 loops, best of 3: 25.2 usec per loop
</pre></div>
</div>
This can be achieved from the <a class="reference internal" href="#python-interface">Python Interface</a> with:
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import timeit
&gt;&gt;&gt; timeit.timeit(&#39;&quot;-&quot;.join(str(n) for n in range(100))&#39;, number=10000)
0.8187260627746582
&gt;&gt;&gt; timeit.timeit(&#39;&quot;-&quot;.join([str(n) for n in range(100)])&#39;, number=10000)
0.7288308143615723
&gt;&gt;&gt; timeit.timeit(&#39;&quot;-&quot;.join(map(str, range(100)))&#39;, number=10000)
0.5858950614929199
</pre></div>
</div>
Note however that <a class="reference internal" href="#module-timeit" title="timeit: Measure the execution time of small code snippets."><code class="xref py py-mod docutils literal notranslate">timeit</code></a> will automatically determine the number of
repetitions only when the command-line interface is used. In the
<a class="reference internal" href="#timeit-examples">Examples</a> section you can find more advanced examples.
</section>
<section id="python-interface">
<h2>26.6.2. Python Interface<a class="headerlink" href="#python-interface" title="Permalink to this headline">¶</a></h2>
The module defines three convenience functions and a public class:
<dl class="py function">
<dt class="sig sig-object py" id="timeit.timeit">
timeit.timeit(stmt='pass', setup='pass', timer=&lt;default timer&gt;, number=1000000)<a class="headerlink" href="#timeit.timeit" title="Permalink to this definition">¶</a></dt>
<dd>Create a <a class="reference internal" href="#timeit.Timer" title="timeit.Timer"><code class="xref py py-class docutils literal notranslate">Timer</code></a> instance with the given statement, setup code and
timer function and run its <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a> method with number executions.
<div class="versionadded">
New in version 2.6.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="timeit.repeat">
timeit.repeat(stmt='pass', setup='pass', timer=&lt;default timer&gt;, repeat=3, number=1000000)<a class="headerlink" href="#timeit.repeat" title="Permalink to this definition">¶</a></dt>
<dd>Create a <a class="reference internal" href="#timeit.Timer" title="timeit.Timer"><code class="xref py py-class docutils literal notranslate">Timer</code></a> instance with the given statement, setup code and
timer function and run its <a class="reference internal" href="#timeit.Timer.repeat" title="timeit.Timer.repeat"><code class="xref py py-meth docutils literal notranslate">repeat()</code></a> method with the given repeat
count and number executions.
<div class="versionadded">
New in version 2.6.
</div>
</dd></dl>

<dl class="py function">
<dt class="sig sig-object py" id="timeit.default_timer">
timeit.default_timer()<a class="headerlink" href="#timeit.default_timer" title="Permalink to this definition">¶</a></dt>
<dd>Define a default timer, in a platform-specific manner. On Windows,
<a class="reference internal" href="time.html#time.clock" title="time.clock"><code class="xref py py-func docutils literal notranslate">time.clock()</code></a> has microsecond granularity, but <a class="reference internal" href="time.html#time.time" title="time.time"><code class="xref py py-func docutils literal notranslate">time.time()</code></a>’s
granularity is 1/60th of a second. On Unix, <a class="reference internal" href="time.html#time.clock" title="time.clock"><code class="xref py py-func docutils literal notranslate">time.clock()</code></a> has 1/100th of
a second granularity, and <a class="reference internal" href="time.html#time.time" title="time.time"><code class="xref py py-func docutils literal notranslate">time.time()</code></a> is much more precise. On either
platform, <a class="reference internal" href="#timeit.default_timer" title="timeit.default_timer"><code class="xref py py-func docutils literal notranslate">default_timer()</code></a> measures wall clock time, not the CPU
time. This means that other processes running on the same computer may
interfere with the timing.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="timeit.Timer">
class timeit.Timer(stmt='pass', setup='pass', timer=&lt;timer function&gt;)<a class="headerlink" href="#timeit.Timer" title="Permalink to this definition">¶</a></dt>
<dd>Class for timing execution speed of small code snippets.
The constructor takes a statement to be timed, an additional statement used
for setup, and a timer function. Both statements default to <code class="docutils literal notranslate">'pass'</code>;
the timer function is platform-dependent (see the module doc string).
stmt and setup may also contain multiple statements separated by <code class="docutils literal notranslate">;</code>
or newlines, as long as they don’t contain multi-line string literals.
To measure the execution time of the first statement, use the <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a>
method. The <a class="reference internal" href="#timeit.Timer.repeat" title="timeit.Timer.repeat"><code class="xref py py-meth docutils literal notranslate">repeat()</code></a> method is a convenience to call <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a>
multiple times and return a list of results.
<div class="versionchanged">
Changed in version 2.6: The stmt and setup parameters can now also take objects that are
callable without arguments. This will embed calls to them in a timer
function that will then be executed by <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a>. Note that the
timing overhead is a little larger in this case because of the extra
function calls.
</div>
<dl class="py method">
<dt class="sig sig-object py" id="timeit.Timer.timeit">
timeit(number=1000000)<a class="headerlink" href="#timeit.Timer.timeit" title="Permalink to this definition">¶</a></dt>
<dd>Time number executions of the main statement. This executes the setup
statement once, and then returns the time it takes to execute the main
statement a number of times, measured in seconds as a float.
The argument is the number of times through the loop, defaulting to one
million. The main statement, the setup statement and the timer function
to be used are passed to the constructor.
<div class="admonition note">
Note
By default, <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a> temporarily turns off <a class="reference internal" href="../glossary.html#term-garbage-collection">garbage
collection</a> during the timing. The advantage of this approach is that
it makes independent timings more comparable. This disadvantage is
that GC may be an important component of the performance of the
function being measured. If so, GC can be re-enabled as the first
statement in the setup string. For example:
<div class="highlight-default notranslate"><div class="highlight"><pre>timeit.Timer(&#39;for i in xrange(10): oct(i)&#39;, &#39;gc.enable()&#39;).timeit()
</pre></div>
</div>
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="timeit.Timer.repeat">
repeat(repeat=3, number=1000000)<a class="headerlink" href="#timeit.Timer.repeat" title="Permalink to this definition">¶</a></dt>
<dd>Call <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a> a few times.
This is a convenience function that calls the <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a> repeatedly,
returning a list of results. The first argument specifies how many times
to call <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a>. The second argument specifies the number
argument for <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate">timeit()</code></a>.
<div class="admonition note">
Note
It’s tempting to calculate mean and standard deviation from the result
vector and report these. However, this is not very useful.
In a typical case, the lowest value gives a lower bound for how fast
your machine can run the given code snippet; higher values in the
result vector are typically not caused by variability in Python’s
speed, but by other processes interfering with your timing accuracy.
So the <a class="reference internal" href="functions.html#min" title="min"><code class="xref py py-func docutils literal notranslate">min()</code></a> of the result is probably the only number you
should be interested in. After that, you should look at the entire
vector and apply common sense rather than statistics.
</div>
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="timeit.Timer.print_exc">
print_exc(file=None)<a class="headerlink" href="#timeit.Timer.print_exc" title="Permalink to this definition">¶</a></dt>
<dd>Helper to print a traceback from the timed code.
Typical use:
<div class="highlight-default notranslate"><div class="highlight"><pre>t = Timer(...) # outside the try/except
try:
 t.timeit(...) # or t.repeat(...)
except:
 t.print_exc()
</pre></div>
</div>
The advantage over the standard traceback is that source lines in the
compiled template will be displayed. The optional file argument directs
where the traceback is sent; it defaults to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a>.
</dd></dl>

</dd></dl>

</section>
<section id="command-line-interface">
<h2>26.6.3. Command-Line Interface<a class="headerlink" href="#command-line-interface" title="Permalink to this headline">¶</a></h2>
When called as a program from the command line, the following form is used:
<div class="highlight-default notranslate"><div class="highlight"><pre>python -m timeit [-n N] [-r N] [-s S] [-t] [-c] [-h] [statement ...]
</pre></div>
</div>
Where the following options are understood:
<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-n">
-n N, --number=N<a class="headerlink" href="#cmdoption-timeit-n" title="Permalink to this definition">¶</a></dt>
<dd>how many times to execute ‘statement’
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-r">
-r N, --repeat=N<a class="headerlink" href="#cmdoption-timeit-r" title="Permalink to this definition">¶</a></dt>
<dd>how many times to repeat the timer (default 3)
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-s">
-s S, --setup=S<a class="headerlink" href="#cmdoption-timeit-s" title="Permalink to this definition">¶</a></dt>
<dd>statement to be executed once initially (default <code class="docutils literal notranslate">pass</code>)
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-t">
-t, --time<a class="headerlink" href="#cmdoption-timeit-t" title="Permalink to this definition">¶</a></dt>
<dd>use <a class="reference internal" href="time.html#time.time" title="time.time"><code class="xref py py-func docutils literal notranslate">time.time()</code></a> (default on all platforms but Windows)
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-c">
-c, --clock<a class="headerlink" href="#cmdoption-timeit-c" title="Permalink to this definition">¶</a></dt>
<dd>use <a class="reference internal" href="time.html#time.clock" title="time.clock"><code class="xref py py-func docutils literal notranslate">time.clock()</code></a> (default on Windows)
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-v">
-v, --verbose<a class="headerlink" href="#cmdoption-timeit-v" title="Permalink to this definition">¶</a></dt>
<dd>print raw timing results; repeat for more digits precision
</dd></dl>

<dl class="std cmdoption">
<dt class="sig sig-object std" id="cmdoption-timeit-h">
-h, --help<a class="headerlink" href="#cmdoption-timeit-h" title="Permalink to this definition">¶</a></dt>
<dd>print a short usage message and exit
</dd></dl>

A multi-line statement may be given by specifying each line as a separate
statement argument; indented lines are possible by enclosing an argument in
quotes and using leading spaces. Multiple <a class="reference internal" href="#cmdoption-timeit-s"><code class="xref std std-option docutils literal notranslate">-s</code></a> options are treated
similarly.
If <a class="reference internal" href="#cmdoption-timeit-n"><code class="xref std std-option docutils literal notranslate">-n</code></a> is not given, a suitable number of loops is calculated by trying
successive powers of 10 until the total time is at least 0.2 seconds.
<a class="reference internal" href="#timeit.default_timer" title="timeit.default_timer"><code class="xref py py-func docutils literal notranslate">default_timer()</code></a> measurations can be affected by other programs running on
the same machine, so
the best thing to do when accurate timing is necessary is to repeat
the timing a few times and use the best time. The <a class="reference internal" href="#cmdoption-timeit-r"><code class="xref std std-option docutils literal notranslate">-r</code></a> option is good
for this; the default of 3 repetitions is probably enough in most cases. On
Unix, you can use <a class="reference internal" href="time.html#time.clock" title="time.clock"><code class="xref py py-func docutils literal notranslate">time.clock()</code></a> to measure CPU time.
<div class="admonition note">
Note
There is a certain baseline overhead associated with executing a pass statement.
The code here doesn’t try to hide it, but you should be aware of it. The
baseline overhead can be measured by invoking the program without arguments, and
it might differ between Python versions. Also, to fairly compare older Python
versions to Python 2.3, you may want to use Python’s <code class="xref std std-option docutils literal notranslate">-O</code>
option (see <a class="reference internal" href="../using/cmdline.html#using-on-optimizations">Optimizations</a>) for
the older versions to avoid timing <code class="docutils literal notranslate">SET_LINENO</code> instructions.
</div>
</section>
<section id="examples">
<h2>26.6.4. Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
It is possible to provide a setup statement that is executed only once at the beginning:
<div class="highlight-sh notranslate"><div class="highlight"><pre>$ python -m timeit -s &#39;text = &quot;sample string&quot;; char = &quot;g&quot;&#39; &#39;char in text&#39;
10000000 loops, best of 3: 0.0877 usec per loop
$ python -m timeit -s &#39;text = &quot;sample string&quot;; char = &quot;g&quot;&#39; &#39;text.find(char)&#39;
1000000 loops, best of 3: 0.342 usec per loop
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import timeit
&gt;&gt;&gt; timeit.timeit(&#39;char in text&#39;, setup=&#39;text = &quot;sample string&quot;; char = &quot;g&quot;&#39;)
0.41440500499993504
&gt;&gt;&gt; timeit.timeit(&#39;text.find(char)&#39;, setup=&#39;text = &quot;sample string&quot;; char = &quot;g&quot;&#39;)
1.7246671520006203
</pre></div>
</div>
The same can be done using the <a class="reference internal" href="#timeit.Timer" title="timeit.Timer"><code class="xref py py-class docutils literal notranslate">Timer</code></a> class and its methods:
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import timeit
&gt;&gt;&gt; t = timeit.Timer(&#39;char in text&#39;, setup=&#39;text = &quot;sample string&quot;; char = &quot;g&quot;&#39;)
&gt;&gt;&gt; t.timeit()
0.3955516149999312
&gt;&gt;&gt; t.repeat()
[0.40193588800002544, 0.3960157959998014, 0.39594301399984033]
</pre></div>
</div>
The following examples show how to time expressions that contain multiple lines.
Here we compare the cost of using <a class="reference internal" href="functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> vs. <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate">try</code></a>/<a class="reference internal" href="../reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate">except</code></a>
to test for missing and present object attributes:
<div class="highlight-sh notranslate"><div class="highlight"><pre>$ python -m timeit &#39;try:&#39; &#39; str.__nonzero__&#39; &#39;except AttributeError:&#39; &#39; pass&#39;
100000 loops, best of 3: 15.7 usec per loop
$ python -m timeit &#39;if hasattr(str, &quot;__nonzero__&quot;): pass&#39;
100000 loops, best of 3: 4.26 usec per loop

$ python -m timeit &#39;try:&#39; &#39; int.__nonzero__&#39; &#39;except AttributeError:&#39; &#39; pass&#39;
1000000 loops, best of 3: 1.43 usec per loop
$ python -m timeit &#39;if hasattr(int, &quot;__nonzero__&quot;): pass&#39;
100000 loops, best of 3: 2.23 usec per loop
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import timeit
&gt;&gt;&gt; # attribute is missing
&gt;&gt;&gt; s = &quot;&quot;&quot;\
... try:
... str.__nonzero__
... except AttributeError:
... pass
... &quot;&quot;&quot;
&gt;&gt;&gt; timeit.timeit(stmt=s, number=100000)
0.9138244460009446
&gt;&gt;&gt; s = &quot;if hasattr(str, &#39;__bool__&#39;): pass&quot;
&gt;&gt;&gt; timeit.timeit(stmt=s, number=100000)
0.5829014980008651
&gt;&gt;&gt;
&gt;&gt;&gt; # attribute is present
&gt;&gt;&gt; s = &quot;&quot;&quot;\
... try:
... int.__nonzero__
... except AttributeError:
... pass
... &quot;&quot;&quot;
&gt;&gt;&gt; timeit.timeit(stmt=s, number=100000)
0.04215312199994514
&gt;&gt;&gt; s = &quot;if hasattr(int, &#39;__bool__&#39;): pass&quot;
&gt;&gt;&gt; timeit.timeit(stmt=s, number=100000)
0.08588060699912603
</pre></div>
</div>
To give the <a class="reference internal" href="#module-timeit" title="timeit: Measure the execution time of small code snippets."><code class="xref py py-mod docutils literal notranslate">timeit</code></a> module access to functions you define, you can pass a
setup parameter which contains an import statement:
<div class="highlight-default notranslate"><div class="highlight"><pre>def test():
 &quot;&quot;&quot;Stupid test function&quot;&quot;&quot;
 L = []
 for i in range(100):
 L.append(i)

if __name__ == &#39;__main__&#39;:
 import timeit
 print(timeit.timeit(&quot;test()&quot;, setup=&quot;from __main__ import test&quot;))
</pre></div>
</div>
</section>
</section>

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<li><a class="reference internal" href="#basic-examples">26.6.1. Basic Examples</a></li>
<li><a class="reference internal" href="#python-interface">26.6.2. Python Interface</a></li>
<li><a class="reference internal" href="#command-line-interface">26.6.3. Command-Line Interface</a></li>
<li><a class="reference internal" href="#examples">26.6.4. Examples</a></li>
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