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Interface</a></li>111<li><a class="reference internal" href="#examples">Examples</a></li>112</ul>113</li>114</ul>115 116 </div>117 <div>118 <h4>Previous topic</h4>119 <p class="topless"><a href="pstats.html"120 title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pstats</span></code> — Statistics for profilers</a></p>121 </div>122 <div>123 <h4>Next topic</h4>124 <p class="topless"><a href="trace.html"125 title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">trace</span></code> — Trace or track Python statement execution</a></p>126 </div>127 <script>128 document.addEventListener('DOMContentLoaded', () => {129 const title = document.querySelector('meta[property="og:title"]').content;130 const elements = document.querySelectorAll('.improvepage');131 const pageurl = window.location.href.split('?')[0];132 elements.forEach(element => {133 const url = new URL(element.href.split('?')[0].replace("-nojs", 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notranslate"><span class="pre">timeit</span></code> — Measure execution time of small code snippets</a></li>191 <li class="right">192 193 194 <div class="inline-search" role="search">195 <form class="inline-search" action="../search.html" method="get">196 <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box">197 <input type="submit" value="Go">198 </form>199 </div>200 |201 </li>202 <li class="right">203<label class="theme-selector-label">204 Theme205 <select class="theme-selector" oninput="activateTheme(this.value)">206 <option value="auto" selected>Auto</option>207 <option value="light">Light</option>208 <option value="dark">Dark</option>209 </select>210</label> |</li>211 212 </ul>213 </div> 214 215 <div class="document">216 <div class="documentwrapper">217 <div class="bodywrapper">218 <div class="body" role="main">219 220 <section id="module-timeit">221<span id="timeit-measure-execution-time-of-small-code-snippets"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code> — Measure execution time of small code snippets<a class="headerlink" href="#module-timeit" title="Link to this heading">¶</a></h1>222<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/main/Lib/timeit.py">Lib/timeit.py</a></p>223<hr class="docutils" id="index-0" />224<p>This module provides a simple way to time small bits of Python code. It has both225a <a class="reference internal" href="#timeit-command-line-interface"><span class="std std-ref">Command-Line Interface</span></a> as well as a <a class="reference internal" href="#python-interface"><span class="std std-ref">callable</span></a>226one. It avoids a number of common traps for measuring execution times.227See also Tim Peters’ introduction to the “Algorithms” chapter in the second228edition of <em>Python Cookbook</em>, published by O’Reilly.</p>229<section id="basic-examples">230<h2>Basic Examples<a class="headerlink" href="#basic-examples" title="Link to this heading">¶</a></h2>231<p>The following example shows how the <a class="reference internal" href="#timeit-command-line-interface"><span class="std std-ref">Command-Line Interface</span></a>232can be used to compare three different expressions:</p>233<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"'-'.join(str(n) for n in range(100))"</span>234<span class="go">10000 loops, best of 5: 30.2 usec per loop</span>235<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"'-'.join([str(n) for n in range(100)])"</span>236<span class="go">10000 loops, best of 5: 27.5 usec per loop</span>237<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"'-'.join(map(str, range(100)))"</span>238<span class="go">10000 loops, best of 5: 23.2 usec per loop</span>239</pre></div>240</div>241<p>This can be achieved from the <a class="reference internal" href="#python-interface"><span class="std std-ref">Python Interface</span></a> with:</p>242<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>243<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'"-".join(str(n) for n in range(100))'</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">10000</span><span class="p">)</span>244<span class="go">0.3018611848820001</span>245<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'"-".join([str(n) for n in range(100)])'</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">10000</span><span class="p">)</span>246<span class="go">0.2727368790656328</span>247<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'"-".join(map(str, range(100)))'</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">10000</span><span class="p">)</span>248<span class="go">0.23702679807320237</span>249</pre></div>250</div>251<p>A callable can also be passed from the <a class="reference internal" href="#python-interface"><span class="std std-ref">Python Interface</span></a>:</p>252<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="k">lambda</span><span class="p">:</span> <span class="s2">"-"</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="nb">str</span><span class="p">,</span> <span class="nb">range</span><span class="p">(</span><span class="mi">100</span><span class="p">))),</span> <span class="n">number</span><span class="o">=</span><span class="mi">10000</span><span class="p">)</span>253<span class="go">0.19665591977536678</span>254</pre></div>255</div>256<p>Note however that <a class="reference internal" href="#timeit.timeit" title="timeit.timeit"><code class="xref py py-func docutils literal notranslate"><span class="pre">timeit()</span></code></a> will automatically determine the number of257repetitions only when the command-line interface is used. In the258<a class="reference internal" href="#timeit-examples"><span class="std std-ref">Examples</span></a> section you can find more advanced examples.</p>259</section>260<section id="python-interface">261<span id="id1"></span><h2>Python Interface<a class="headerlink" href="#python-interface" title="Link to this heading">¶</a></h2>262<p>The module defines three convenience functions and a public class:</p>263<dl class="py function">264<dt class="sig sig-object py" id="timeit.timeit">265<span class="sig-prename descclassname"><span class="pre">timeit.</span></span><span class="sig-name descname"><span class="pre">timeit</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stmt='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">setup='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timer=<default</span> <span class="pre">timer></span></span></em>, <em class="sig-param"><span class="n"><span class="pre">number=1000000</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">globals=None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.timeit" title="Link to this definition">¶</a></dt>266<dd><p>Create a <a class="reference internal" href="#timeit.Timer" title="timeit.Timer"><code class="xref py py-class docutils literal notranslate"><span class="pre">Timer</span></code></a> instance with the given statement, <em>setup</em> code and267<em>timer</em> 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"><span class="pre">timeit()</span></code></a> method with <em>number</em> executions.268The optional <em>globals</em> argument specifies a namespace in which to execute the269code.</p>270<div class="versionchanged">271<p><span class="versionmodified changed">Changed in version 3.5: </span>The optional <em>globals</em> parameter was added.</p>272</div>273</dd></dl>274 275<dl class="py function">276<dt class="sig sig-object py" id="timeit.repeat">277<span class="sig-prename descclassname"><span class="pre">timeit.</span></span><span class="sig-name descname"><span class="pre">repeat</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stmt='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">setup='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timer=<default</span> <span class="pre">timer></span></span></em>, <em class="sig-param"><span class="n"><span class="pre">repeat=5</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">number=1000000</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">globals=None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.repeat" title="Link to this definition">¶</a></dt>278<dd><p>Create a <a class="reference internal" href="#timeit.Timer" title="timeit.Timer"><code class="xref py py-class docutils literal notranslate"><span class="pre">Timer</span></code></a> instance with the given statement, <em>setup</em> code and279<em>timer</em> 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"><span class="pre">repeat()</span></code></a> method with the given <em>repeat</em>280count and <em>number</em> executions. The optional <em>globals</em> argument specifies a281namespace in which to execute the code.</p>282<div class="versionchanged">283<p><span class="versionmodified changed">Changed in version 3.5: </span>The optional <em>globals</em> parameter was added.</p>284</div>285<div class="versionchanged">286<p><span class="versionmodified changed">Changed in version 3.7: </span>Default value of <em>repeat</em> changed from 3 to 5.</p>287</div>288</dd></dl>289 290<dl class="py function">291<dt class="sig sig-object py" id="timeit.default_timer">292<span class="sig-prename descclassname"><span class="pre">timeit.</span></span><span class="sig-name descname"><span class="pre">default_timer</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#timeit.default_timer" title="Link to this definition">¶</a></dt>293<dd><p>The default timer, which is always time.perf_counter(), returns float seconds.294An alternative, time.perf_counter_ns, returns integer nanoseconds.</p>295<div class="versionchanged">296<p><span class="versionmodified changed">Changed in version 3.3: </span><a class="reference internal" href="time.html#time.perf_counter" title="time.perf_counter"><code class="xref py py-func docutils literal notranslate"><span class="pre">time.perf_counter()</span></code></a> is now the default timer.</p>297</div>298</dd></dl>299 300<dl class="py class">301<dt class="sig sig-object py" id="timeit.Timer">302<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">timeit.</span></span><span class="sig-name descname"><span class="pre">Timer</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stmt='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">setup='pass'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timer=<timer</span> <span class="pre">function></span></span></em>, <em class="sig-param"><span class="n"><span class="pre">globals=None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer" title="Link to this definition">¶</a></dt>303<dd><p>Class for timing execution speed of small code snippets.</p>304<p>The constructor takes a statement to be timed, an additional statement used305for setup, and a timer function. Both statements default to <code class="docutils literal notranslate"><span class="pre">'pass'</span></code>;306the timer function is platform-dependent (see the module doc string).307<em>stmt</em> and <em>setup</em> may also contain multiple statements separated by <code class="docutils literal notranslate"><span class="pre">;</span></code>308or newlines, as long as they don’t contain multi-line string literals. The309statement will by default be executed within timeit’s namespace; this behavior310can be controlled by passing a namespace to <em>globals</em>.</p>311<p>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"><span class="pre">timeit()</span></code></a>312method. The <a class="reference internal" href="#timeit.Timer.repeat" title="timeit.Timer.repeat"><code class="xref py py-meth docutils literal notranslate"><span class="pre">repeat()</span></code></a> and <a class="reference internal" href="#timeit.Timer.autorange" title="timeit.Timer.autorange"><code class="xref py py-meth docutils literal notranslate"><span class="pre">autorange()</span></code></a> methods are convenience313methods to call <code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code> multiple times.</p>314<p>The execution time of <em>setup</em> is excluded from the overall timed execution run.</p>315<p>The <em>stmt</em> and <em>setup</em> parameters can also take objects that are callable316without arguments. This will embed calls to them in a timer function that317will 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"><span class="pre">timeit()</span></code></a>. Note that the timing overhead is a318little larger in this case because of the extra function calls.</p>319<div class="versionchanged">320<p><span class="versionmodified changed">Changed in version 3.5: </span>The optional <em>globals</em> parameter was added.</p>321</div>322<dl class="py method">323<dt class="sig sig-object py" id="timeit.Timer.timeit">324<span class="sig-name descname"><span class="pre">timeit</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">number</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">1000000</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.timeit" title="Link to this definition">¶</a></dt>325<dd><p>Time <em>number</em> executions of the main statement. This executes the setup326statement once, and then returns the time it takes to execute the main327statement a number of times. The default timer returns seconds as a float.328The argument is the number of times through the loop, defaulting to one329million. The main statement, the setup statement and the timer function330to be used are passed to the constructor.</p>331<div class="admonition note">332<p class="admonition-title">Note</p>333<p>By default, <code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code> temporarily turns off <a class="reference internal" href="../glossary.html#term-garbage-collection"><span class="xref std std-term">garbage334collection</span></a> during the timing. The advantage of this approach is that335it makes independent timings more comparable. The disadvantage is336that GC may be an important component of the performance of the337function being measured. If so, GC can be re-enabled as the first338statement in the <em>setup</em> string. For example:</p>339<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">timeit</span><span class="o">.</span><span class="n">Timer</span><span class="p">(</span><span class="s1">'for i in range(10): oct(i)'</span><span class="p">,</span> <span class="s1">'gc.enable()'</span><span class="p">)</span><span class="o">.</span><span class="n">timeit</span><span class="p">()</span>340</pre></div>341</div>342</div>343</dd></dl>344 345<dl class="py method">346<dt class="sig sig-object py" id="timeit.Timer.autorange">347<span class="sig-name descname"><span class="pre">autorange</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">callback</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.autorange" title="Link to this definition">¶</a></dt>348<dd><p>Automatically determine 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"><span class="pre">timeit()</span></code></a>.</p>349<p>This is a convenience function that calls <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code></a> repeatedly350so that the total time >= 0.2 second, returning the eventual351(number of loops, time taken for that number of loops). It calls352<code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code> with increasing numbers from the sequence 1, 2, 5,35310, 20, 50, … until the time taken is at least 0.2 seconds.</p>354<p>If <em>callback</em> is given and is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, it will be called after355each trial with two arguments: <code class="docutils literal notranslate"><span class="pre">callback(number,</span> <span class="pre">time_taken)</span></code>.</p>356<div class="versionadded">357<p><span class="versionmodified added">Added in version 3.6.</span></p>358</div>359</dd></dl>360 361<dl class="py method">362<dt class="sig sig-object py" id="timeit.Timer.repeat">363<span class="sig-name descname"><span class="pre">repeat</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">repeat</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">5</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">number</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">1000000</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.repeat" title="Link to this definition">¶</a></dt>364<dd><p>Call <a class="reference internal" href="#timeit.Timer.timeit" title="timeit.Timer.timeit"><code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code></a> a few times.</p>365<p>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"><span class="pre">timeit()</span></code></a> repeatedly,366returning a list of results. The first argument specifies how many times367to call <code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code>. The second argument specifies the <em>number</em>368argument for <code class="xref py py-meth docutils literal notranslate"><span class="pre">timeit()</span></code>.</p>369<div class="admonition note">370<p class="admonition-title">Note</p>371<p>It’s tempting to calculate mean and standard deviation from the result372vector and report these. However, this is not very useful.373In a typical case, the lowest value gives a lower bound for how fast374your machine can run the given code snippet; higher values in the375result vector are typically not caused by variability in Python’s376speed, but by other processes interfering with your timing accuracy.377So the <a class="reference internal" href="functions.html#min" title="min"><code class="xref py py-func docutils literal notranslate"><span class="pre">min()</span></code></a> of the result is probably the only number you378should be interested in. After that, you should look at the entire379vector and apply common sense rather than statistics.</p>380</div>381<div class="versionchanged">382<p><span class="versionmodified changed">Changed in version 3.7: </span>Default value of <em>repeat</em> changed from 3 to 5.</p>383</div>384</dd></dl>385 386<dl class="py method">387<dt class="sig sig-object py" id="timeit.Timer.print_exc">388<span class="sig-name descname"><span class="pre">print_exc</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.print_exc" title="Link to this definition">¶</a></dt>389<dd><p>Helper to print a traceback from the timed code.</p>390<p>Typical use:</p>391<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">t</span> <span class="o">=</span> <span class="n">Timer</span><span class="p">(</span><span class="o">...</span><span class="p">)</span> <span class="c1"># outside the try/except</span>392<span class="k">try</span><span class="p">:</span>393 <span class="n">t</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="o">...</span><span class="p">)</span> <span class="c1"># or t.repeat(...)</span>394<span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span>395 <span class="n">t</span><span class="o">.</span><span class="n">print_exc</span><span class="p">()</span>396</pre></div>397</div>398<p>The advantage over the standard traceback is that source lines in the399compiled template will be displayed. The optional <em>file</em> argument directs400where 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"><span class="pre">sys.stderr</span></code></a>.</p>401</dd></dl>402 403</dd></dl>404 405</section>406<section id="command-line-interface">407<span id="timeit-command-line-interface"></span><h2>Command-Line Interface<a class="headerlink" href="#command-line-interface" title="Link to this heading">¶</a></h2>408<p>When called as a program from the command line, the following form is used:</p>409<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">python</span> <span class="o">-</span><span class="n">m</span> <span class="n">timeit</span> <span class="p">[</span><span class="o">-</span><span class="n">n</span> <span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">r</span> <span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">u</span> <span class="n">U</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">s</span> <span class="n">S</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">p</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">v</span><span class="p">]</span> <span class="p">[</span><span class="o">-</span><span class="n">h</span><span class="p">]</span> <span class="p">[</span><span class="n">statement</span> <span class="o">...</span><span class="p">]</span>410</pre></div>411</div>412<p>Where the following options are understood:</p>413<dl class="std option">414<dt class="sig sig-object std" id="cmdoption-timeit-n">415<span id="cmdoption-timeit-number"></span><span class="sig-name descname"><span class="pre">-n</span></span><span class="sig-prename descclassname"> <span class="pre">N</span></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--number</span></span><span class="sig-prename descclassname"><span class="pre">=N</span></span><a class="headerlink" href="#cmdoption-timeit-n" title="Link to this definition">¶</a></dt>416<dd><p>how many times to execute ‘statement’</p>417</dd></dl>418 419<dl class="std option">420<dt class="sig sig-object std" id="cmdoption-timeit-r">421<span id="cmdoption-timeit-repeat"></span><span class="sig-name descname"><span class="pre">-r</span></span><span class="sig-prename descclassname"> <span class="pre">N</span></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--repeat</span></span><span class="sig-prename descclassname"><span class="pre">=N</span></span><a class="headerlink" href="#cmdoption-timeit-r" title="Link to this definition">¶</a></dt>422<dd><p>how many times to repeat the timer (default 5)</p>423</dd></dl>424 425<dl class="std option">426<dt class="sig sig-object std" id="cmdoption-timeit-s">427<span id="cmdoption-timeit-setup"></span><span class="sig-name descname"><span class="pre">-s</span></span><span class="sig-prename descclassname"> <span class="pre">S</span></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--setup</span></span><span class="sig-prename descclassname"><span class="pre">=S</span></span><a class="headerlink" href="#cmdoption-timeit-s" title="Link to this definition">¶</a></dt>428<dd><p>statement to be executed once initially (default <code class="docutils literal notranslate"><span class="pre">pass</span></code>)</p>429</dd></dl>430 431<dl class="std option">432<dt class="sig sig-object std" id="cmdoption-timeit-p">433<span id="cmdoption-timeit-process"></span><span class="sig-name descname"><span class="pre">-p</span></span><span class="sig-prename descclassname"></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--process</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-timeit-p" title="Link to this definition">¶</a></dt>434<dd><p>measure process time, not wallclock time, using <a class="reference internal" href="time.html#time.process_time" title="time.process_time"><code class="xref py py-func docutils literal notranslate"><span class="pre">time.process_time()</span></code></a>435instead of <a class="reference internal" href="time.html#time.perf_counter" title="time.perf_counter"><code class="xref py py-func docutils literal notranslate"><span class="pre">time.perf_counter()</span></code></a>, which is the default</p>436<div class="versionadded">437<p><span class="versionmodified added">Added in version 3.3.</span></p>438</div>439</dd></dl>440 441<dl class="std option">442<dt class="sig sig-object std" id="cmdoption-timeit-u">443<span id="cmdoption-timeit-unit"></span><span class="sig-name descname"><span class="pre">-u</span></span><span class="sig-prename descclassname"></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--unit</span></span><span class="sig-prename descclassname"><span class="pre">=U</span></span><a class="headerlink" href="#cmdoption-timeit-u" title="Link to this definition">¶</a></dt>444<dd><p>specify a time unit for timer output; can select <code class="docutils literal notranslate"><span class="pre">nsec</span></code>, <code class="docutils literal notranslate"><span class="pre">usec</span></code>, <code class="docutils literal notranslate"><span class="pre">msec</span></code>, or <code class="docutils literal notranslate"><span class="pre">sec</span></code></p>445<div class="versionadded">446<p><span class="versionmodified added">Added in version 3.5.</span></p>447</div>448</dd></dl>449 450<dl class="std option">451<dt class="sig sig-object std" id="cmdoption-timeit-v">452<span id="cmdoption-timeit-verbose"></span><span class="sig-name descname"><span class="pre">-v</span></span><span class="sig-prename descclassname"></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--verbose</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-timeit-v" title="Link to this definition">¶</a></dt>453<dd><p>print raw timing results; repeat for more digits precision</p>454</dd></dl>455 456<dl class="std option">457<dt class="sig sig-object std" id="cmdoption-timeit-h">458<span id="cmdoption-timeit-help"></span><span class="sig-name descname"><span class="pre">-h</span></span><span class="sig-prename descclassname"></span><span class="sig-prename descclassname"><span class="pre">,</span> </span><span class="sig-name descname"><span class="pre">--help</span></span><span class="sig-prename descclassname"></span><a class="headerlink" href="#cmdoption-timeit-h" title="Link to this definition">¶</a></dt>459<dd><p>print a short usage message and exit</p>460</dd></dl>461 462<p>A multi-line statement may be given by specifying each line as a separate463statement argument; indented lines are possible by enclosing an argument in464quotes and using leading spaces. Multiple <a class="reference internal" href="#cmdoption-timeit-s"><code class="xref std std-option docutils literal notranslate"><span class="pre">-s</span></code></a> options are treated465similarly.</p>466<p>If <a class="reference internal" href="#cmdoption-timeit-n"><code class="xref std std-option docutils literal notranslate"><span class="pre">-n</span></code></a> is not given, a suitable number of loops is calculated by trying467increasing numbers from the sequence 1, 2, 5, 10, 20, 50, … until the total468time is at least 0.2 seconds.</p>469<p><a class="reference internal" href="#timeit.default_timer" title="timeit.default_timer"><code class="xref py py-func docutils literal notranslate"><span class="pre">default_timer()</span></code></a> measurements can be affected by other programs running on470the same machine, so the best thing to do when accurate timing is necessary is471to 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"><span class="pre">-r</span></code></a>472option is good for this; the default of 5 repetitions is probably enough in473most cases. You can use <a class="reference internal" href="time.html#time.process_time" title="time.process_time"><code class="xref py py-func docutils literal notranslate"><span class="pre">time.process_time()</span></code></a> to measure CPU time.</p>474<div class="admonition note">475<p class="admonition-title">Note</p>476<p>There is a certain baseline overhead associated with executing a pass statement.477The code here doesn’t try to hide it, but you should be aware of it. The478baseline overhead can be measured by invoking the program without arguments,479and it might differ between Python versions.</p>480</div>481</section>482<section id="examples">483<span id="timeit-examples"></span><h2>Examples<a class="headerlink" href="#examples" title="Link to this heading">¶</a></h2>484<p>It is possible to provide a setup statement that is executed only once at the beginning:</p>485<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span>-s<span class="w"> </span><span class="s2">"text = 'sample string'; char = 'g'"</span><span class="w"> </span><span class="s2">"char in text"</span>486<span class="go">5000000 loops, best of 5: 0.0877 usec per loop</span>487<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span>-s<span class="w"> </span><span class="s2">"text = 'sample string'; char = 'g'"</span><span class="w"> </span><span class="s2">"text.find(char)"</span>488<span class="go">1000000 loops, best of 5: 0.342 usec per loop</span>489</pre></div>490</div>491<p>In the output, there are three fields. The loop count, which tells you how many492times the statement body was run per timing loop repetition. The repetition493count (‘best of 5’) which tells you how many times the timing loop was494repeated, and finally the time the statement body took on average within the495best repetition of the timing loop. That is, the time the fastest repetition496took divided by the loop count.</p>497<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>498<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'char in text'</span><span class="p">,</span> <span class="n">setup</span><span class="o">=</span><span class="s1">'text = "sample string"; char = "g"'</span><span class="p">)</span>499<span class="go">0.41440500499993504</span>500<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'text.find(char)'</span><span class="p">,</span> <span class="n">setup</span><span class="o">=</span><span class="s1">'text = "sample string"; char = "g"'</span><span class="p">)</span>501<span class="go">1.7246671520006203</span>502</pre></div>503</div>504<p>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"><span class="pre">Timer</span></code></a> class and its methods:</p>505<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>506<span class="gp">>>> </span><span class="n">t</span> <span class="o">=</span> <span class="n">timeit</span><span class="o">.</span><span class="n">Timer</span><span class="p">(</span><span class="s1">'char in text'</span><span class="p">,</span> <span class="n">setup</span><span class="o">=</span><span class="s1">'text = "sample string"; char = "g"'</span><span class="p">)</span>507<span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">timeit</span><span class="p">()</span>508<span class="go">0.3955516149999312</span>509<span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">repeat</span><span class="p">()</span>510<span class="go">[0.40183617287970225, 0.37027556854118704, 0.38344867356679524, 0.3712595970846668, 0.37866875250654886]</span>511</pre></div>512</div>513<p>The following examples show how to time expressions that contain multiple lines.514Here 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"><span class="pre">hasattr()</span></code></a> vs. <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a>/<a class="reference internal" href="../reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">except</span></code></a>515to test for missing and present object attributes:</p>516<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"try:"</span><span class="w"> </span><span class="s2">" str.__bool__"</span><span class="w"> </span><span class="s2">"except AttributeError:"</span><span class="w"> </span><span class="s2">" pass"</span>517<span class="go">20000 loops, best of 5: 15.7 usec per loop</span>518<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"if hasattr(str, '__bool__'): pass"</span>519<span class="go">50000 loops, best of 5: 4.26 usec per loop</span>520 521<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"try:"</span><span class="w"> </span><span class="s2">" int.__bool__"</span><span class="w"> </span><span class="s2">"except AttributeError:"</span><span class="w"> </span><span class="s2">" pass"</span>522<span class="go">200000 loops, best of 5: 1.43 usec per loop</span>523<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s2">"if hasattr(int, '__bool__'): pass"</span>524<span class="go">100000 loops, best of 5: 2.23 usec per loop</span>525</pre></div>526</div>527<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>528<span class="gp">>>> </span><span class="c1"># attribute is missing</span>529<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"""</span><span class="se">\</span>530<span class="gp">... </span><span class="s2">try:</span>531<span class="gp">... </span><span class="s2"> str.__bool__</span>532<span class="gp">... </span><span class="s2">except AttributeError:</span>533<span class="gp">... </span><span class="s2"> pass</span>534<span class="gp">... </span><span class="s2">"""</span>535<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="n">stmt</span><span class="o">=</span><span class="n">s</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">100000</span><span class="p">)</span>536<span class="go">0.9138244460009446</span>537<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"if hasattr(str, '__bool__'): pass"</span>538<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="n">stmt</span><span class="o">=</span><span class="n">s</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">100000</span><span class="p">)</span>539<span class="go">0.5829014980008651</span>540<span class="gp">>>></span>541<span class="gp">>>> </span><span class="c1"># attribute is present</span>542<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"""</span><span class="se">\</span>543<span class="gp">... </span><span class="s2">try:</span>544<span class="gp">... </span><span class="s2"> int.__bool__</span>545<span class="gp">... </span><span class="s2">except AttributeError:</span>546<span class="gp">... </span><span class="s2"> pass</span>547<span class="gp">... </span><span class="s2">"""</span>548<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="n">stmt</span><span class="o">=</span><span class="n">s</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">100000</span><span class="p">)</span>549<span class="go">0.04215312199994514</span>550<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"if hasattr(int, '__bool__'): pass"</span>551<span class="gp">>>> </span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="n">stmt</span><span class="o">=</span><span class="n">s</span><span class="p">,</span> <span class="n">number</span><span class="o">=</span><span class="mi">100000</span><span class="p">)</span>552<span class="go">0.08588060699912603</span>553</pre></div>554</div>555<p>To give the <code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code> module access to functions you define, you can pass a556<em>setup</em> parameter which contains an import statement:</p>557<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">test</span><span class="p">():</span>558<span class="w"> </span><span class="sd">"""Stupid test function"""</span>559 <span class="n">L</span> <span class="o">=</span> <span class="p">[</span><span class="n">i</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">100</span><span class="p">)]</span>560 561<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>562 <span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>563 <span class="nb">print</span><span class="p">(</span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s2">"test()"</span><span class="p">,</span> <span class="n">setup</span><span class="o">=</span><span class="s2">"from __main__ import test"</span><span class="p">))</span>564</pre></div>565</div>566<p>Another option is to pass <a class="reference internal" href="functions.html#globals" title="globals"><code class="xref py py-func docutils literal notranslate"><span class="pre">globals()</span></code></a> to the <em>globals</em> parameter, which will cause the code567to be executed within your current global namespace. This can be more convenient568than individually specifying imports:</p>569<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span><span class="w"> </span><span class="nf">f</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>570 <span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span>571<span class="k">def</span><span class="w"> </span><span class="nf">g</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>572 <span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">4</span>573<span class="k">def</span><span class="w"> </span><span class="nf">h</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>574 <span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">8</span>575 576<span class="kn">import</span><span class="w"> </span><span class="nn">timeit</span>577<span class="nb">print</span><span class="p">(</span><span class="n">timeit</span><span class="o">.</span><span class="n">timeit</span><span class="p">(</span><span class="s1">'[func(42) for func in (f,g,h)]'</span><span class="p">,</span> <span class="nb">globals</span><span class="o">=</span><span class="nb">globals</span><span class="p">()))</span>578</pre></div>579</div>580</section>581</section>582 583 584 <div class="clearer"></div>585 </div>586 </div>587 </div>588 <div class="sphinxsidebar" role="navigation" aria-label="Main">589 <div class="sphinxsidebarwrapper">590 <div>591 <h3><a href="../contents.html">Table of Contents</a></h3>592 <ul>593<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code> — Measure execution time of small code snippets</a><ul>594<li><a class="reference internal" href="#basic-examples">Basic Examples</a></li>595<li><a class="reference internal" href="#python-interface">Python Interface</a></li>596<li><a class="reference internal" href="#command-line-interface">Command-Line Interface</a></li>597<li><a class="reference internal" href="#examples">Examples</a></li>598</ul>599</li>600</ul>601 602 </div>603 <div>604 <h4>Previous topic</h4>605 <p class="topless"><a href="pstats.html"606 title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pstats</span></code> — Statistics for profilers</a></p>607 </div>608 <div>609 <h4>Next topic</h4>610 <p class="topless"><a href="trace.html"611 title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">trace</span></code> — Trace or track Python statement execution</a></p>612 </div>613 <script>614 document.addEventListener('DOMContentLoaded', () => {615 const title = document.querySelector('meta[property="og:title"]').content;616 const elements = document.querySelectorAll('.improvepage');617 const pageurl = window.location.href.split('?')[0];618 elements.forEach(element => {619 const url = new URL(element.href.split('?')[0].replace("-nojs", ""));620 url.searchParams.set('pagetitle', title);621 url.searchParams.set('pageurl', pageurl);622 url.searchParams.set('pagesource', "library/timeit.rst");623 element.href = url.toString();624 });625 });626 </script>627 <div role="note" aria-label="source link">628 <h3>This page</h3>629 <ul class="this-page-menu">630 <li><a href="../bugs.html">Report a bug</a></li>631 <li><a class="improvepage" href="../improve-page-nojs.html">Improve this page</a></li>632 <li>633 <a href="https://github.com/python/cpython/blob/main/Doc/library/timeit.rst?plain=1"634 rel="nofollow">Show source635 </a>636 </li>637 638 </ul>639 </div>640 </div>641<div id="sidebarbutton" title="Collapse sidebar">642<span>«</span>643</div>644 645 </div>646 <div class="clearer"></div>647 </div> 648 <div class="related" role="navigation" aria-label="Related">649 <h3>Navigation</h3>650 <ul>651 <li class="right" style="margin-right: 10px">652 <a href="../genindex.html" title="General Index"653 >index</a></li>654 <li class="right" >655 <a href="../py-modindex.html" title="Python Module Index"656 >modules</a> |</li>657 <li class="right" >658 <a href="trace.html" title="trace — Trace or track Python statement execution"659 >next</a> |</li>660 <li class="right" >661 <a href="pstats.html" title="pstats — Statistics for profilers"662 >previous</a> |</li>663 664 <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; 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