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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code> --- 测量小代码片段的执行时间</a><ul>
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<section id="module-timeit">
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<span id="timeit-measure-execution-time-of-small-code-snippets"></span><h1><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"><span class="pre">timeit</span></code></a> --- 测量小代码片段的执行时间<a class="headerlink" href="#module-timeit" title="永久链接至标题">¶</a></h1>
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<p><strong>源码：</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/timeit.py">Lib/timeit.py</a></p>
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<hr class="docutils" id="index-0" />
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<p>该模块提供了一种简单的方法来计算一小段 Python 代码的耗时。它有 <a class="reference internal" href="#timeit-command-line-interface"><span class="std std-ref">命令行界面</span></a> 以及一个 <a class="reference internal" href="#python-interface"><span class="std std-ref">可调用</span></a> 方法。它避免了许多用于测量执行时间的常见陷阱。另见 Tim Peters 对 O'Reilly 出版的 <em>Python Cookbook</em> 中“算法”章节的介绍。</p>
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<section id="basic-examples">
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<h2>基本示例<a class="headerlink" href="#basic-examples" title="永久链接至标题">¶</a></h2>
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<p>以下示例显示了如何使用 <a class="reference internal" href="#timeit-command-line-interface"><span class="std std-ref">命令行界面</span></a> 来比较三个不同的表达式：</p>
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<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python3<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'"-".join(str(n) for n in range(100))'</span>
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<span class="go">10000 loops, best of 5: 30.2 usec per loop</span>
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<span class="gp">$ </span>python3<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'"-".join([str(n) for n in range(100)])'</span>
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<span class="go">10000 loops, best of 5: 27.5 usec per loop</span>
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<span class="gp">$ </span>python3<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'"-".join(map(str, range(100)))'</span>
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<span class="go">10000 loops, best of 5: 23.2 usec per loop</span>
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</pre></div>
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</div>
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<p>这可以通过 <a class="reference internal" href="#python-interface"><span class="std std-ref">Python 接口</span></a> 实现</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">timeit</span>
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<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>
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<span class="go">0.3018611848820001</span>
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<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>
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<span class="go">0.2727368790656328</span>
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<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>
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<span class="go">0.23702679807320237</span>
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</pre></div>
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</div>
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<p>从 <a class="reference internal" href="#python-interface"><span class="std std-ref">Python 接口</span></a> 还可以传出一个可调用对象:</p>
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<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>
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<span class="go">0.19665591977536678</span>
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</pre></div>
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</div>
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<p>但请注意 <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> 仅在使用命令行界面时会自动确定重复次数。 在 <a class="reference internal" href="#timeit-examples"><span class="std std-ref">例子</span></a> 一节你可以找到更多的进阶示例。</p>
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</section>
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<section id="python-interface">
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<span id="id1"></span><h2>Python 接口<a class="headerlink" href="#python-interface" title="永久链接至标题">¶</a></h2>
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<p>该模块定义了三个便利函数和一个公共类：</p>
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<dl class="function">
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<dt id="timeit.timeit">
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<code class="sig-prename descclassname">timeit.</code><code class="sig-name descname">timeit</code><span class="sig-paren">(</span><em class="sig-param">stmt='pass'</em>, <em class="sig-param">setup='pass'</em>, <em class="sig-param">timer=<default timer></em>, <em class="sig-param">number=1000000</em>, <em class="sig-param">globals=None</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.timeit" title="永久链接至目标">¶</a></dt>
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<dd><p>使用给定语句、 <em>setup</em> 代码和 <em>timer</em> 函数创建一个 <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> 实例，并执行 <em>number</em> 次其 <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> 方法。可选的 <em>globals</em> 参数指定用于执行代码的命名空间。</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.5 版更改: </span>添加可选参数 <em>globals</em> 。</p>
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</div>
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</dd></dl>
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<dl class="function">
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<dt id="timeit.repeat">
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<code class="sig-prename descclassname">timeit.</code><code class="sig-name descname">repeat</code><span class="sig-paren">(</span><em class="sig-param">stmt='pass'</em>, <em class="sig-param">setup='pass'</em>, <em class="sig-param">timer=<default timer></em>, <em class="sig-param">repeat=5</em>, <em class="sig-param">number=1000000</em>, <em class="sig-param">globals=None</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.repeat" title="永久链接至目标">¶</a></dt>
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<dd><p>使用给定语句、 <em>setup</em> 代码和 <em>timer</em> 函数创建一个 <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> 实例，并使用给定的 <em>repeat</em> 计数和 <em>number</em> 执行运行其 <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> 方法。可选的 <em>globals</em> 参数指定用于执行代码的命名空间。</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.5 版更改: </span>添加可选参数 <em>globals</em> 。</p>
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</div>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.7 版更改: </span><em>repeat</em> 的默认值由 3 更改为 5 。</p>
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</div>
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</dd></dl>
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<dl class="function">
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<dt id="timeit.default_timer">
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<code class="sig-prename descclassname">timeit.</code><code class="sig-name descname">default_timer</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#timeit.default_timer" title="永久链接至目标">¶</a></dt>
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<dd><p>默认的计时器，总是 <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> 。</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.3 版更改: </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> 现在是默认计时器。</p>
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</div>
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</dd></dl>
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<dl class="class">
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<dt id="timeit.Timer">
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<em class="property">class </em><code class="sig-prename descclassname">timeit.</code><code class="sig-name descname">Timer</code><span class="sig-paren">(</span><em class="sig-param">stmt='pass'</em>, <em class="sig-param">setup='pass'</em>, <em class="sig-param">timer=<timer function></em>, <em class="sig-param">globals=None</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer" title="永久链接至目标">¶</a></dt>
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<dd><p>用于小代码片段的计数执行速度的类。</p>
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<p>构造函数接受一个将计时的语句、一个用于设置的附加语句和一个定时器函数。两个语句都默认为 <code class="docutils literal notranslate"><span class="pre">'pass'</span></code> ；计时器函数与平台有关（请参阅模块文档字符串）。 <em>stmt</em> 和 <em>setup</em> 也可能包含多个以 <code class="docutils literal notranslate"><span class="pre">;</span></code> 或换行符分隔的语句，只要它们不包含多行字符串文字即可。该语句默认在 timeit 的命名空间内执行；可以通过将命名空间传递给 <em>globals</em> 来控制此行为。</p>
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<p>要测量第一个语句的执行时间，请使用 <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> 方法。 <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> 和 <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> 方法是方便的方法来调用 <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> 多次。</p>
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<p><em>setup</em> 的执行时间从总体计时执行中排除。</p>
|
||
<p><em>stmt</em> 和 <em>setup</em> 参数也可以使用不带参数的可调用对象。这将在一个计时器函数中嵌入对它们的调用，然后由 <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> 执行。请注意，由于额外的函数调用，在这种情况下，计时开销会略大一些。</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.5 版更改: </span>添加可选参数 <em>globals</em> 。</p>
|
||
</div>
|
||
<dl class="method">
|
||
<dt id="timeit.Timer.timeit">
|
||
<code class="sig-name descname">timeit</code><span class="sig-paren">(</span><em class="sig-param">number=1000000</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.timeit" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>执行 <em>number</em> 次主要语句。这将执行一次 setup 语句，然后返回执行主语句多次所需的时间，以秒为单位测量为浮点数。参数是通过循环的次数，默认为一百万。要使用的主语句、 setup 语句和 timer 函数将传递给构造函数。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>默认情况下， <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> 暂时关闭 <a class="reference internal" href="../glossary.html#term-garbage-collection"><span class="xref std std-term">garbage collection</span></a> 。这种方法的优点在于它使独立时序更具可比性。缺点是GC可能是所测量功能性能的重要组成部分。如果是这样，可以在 <em>setup</em> 字符串中的第一个语句重新启用GC。例如:</p>
|
||
<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>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="timeit.Timer.autorange">
|
||
<code class="sig-name descname">autorange</code><span class="sig-paren">(</span><em class="sig-param">callback=None</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.autorange" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>自动决定调用多少次 <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>
|
||
<p>这是一个便利函数，它反复调用 <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> ，以便总时间 >= 0.2 秒，返回最终（循环次数，循环所用的时间）。它调用 <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> 的次数以序列 1, 2, 5, 10, 20, 50, ... 递增，直到所用的时间至少为0.2秒。</p>
|
||
<p>如果给出 <em>callback</em> 并且不是 <code class="docutils literal notranslate"><span class="pre">None</span></code> ，则在每次试验后将使用两个参数调用它： <code class="docutils literal notranslate"><span class="pre">callback(number,</span> <span class="pre">time_taken)</span></code> 。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.6 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="timeit.Timer.repeat">
|
||
<code class="sig-name descname">repeat</code><span class="sig-paren">(</span><em class="sig-param">repeat=5</em>, <em class="sig-param">number=1000000</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.repeat" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>调用 <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> 几次。</p>
|
||
<p>这是一个方便的函数，它反复调用 <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> ，返回结果列表。第一个参数指定调用 <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> 的次数。第二个参数指定 <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> 的 <em>number</em> 参数。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>从结果向量计算并报告平均值和标准差这些是很诱人的。但是，这不是很有用。在典型情况下，最低值给出了机器运行给定代码段的速度的下限；结果向量中较高的值通常不是由Python的速度变化引起的，而是由于其他过程干扰你的计时准确性。所以结果的 <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> 可能是你应该感兴趣的唯一数字。之后，你应该看看整个向量并应用常识而不是统计。</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">在 3.7 版更改: </span><em>repeat</em> 的默认值由 3 更改为 5 。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="method">
|
||
<dt id="timeit.Timer.print_exc">
|
||
<code class="sig-name descname">print_exc</code><span class="sig-paren">(</span><em class="sig-param">file=None</em><span class="sig-paren">)</span><a class="headerlink" href="#timeit.Timer.print_exc" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>帮助程序从计时代码中打印回溯。</p>
|
||
<p>典型使用:</p>
|
||
<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>
|
||
<span class="k">try</span><span class="p">:</span>
|
||
<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>
|
||
<span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span>
|
||
<span class="n">t</span><span class="o">.</span><span class="n">print_exc</span><span class="p">()</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>与标准回溯相比，优势在于将显示已编译模板中的源行。可选的 <em>file</em> 参数指向发送回溯的位置；它默认为 <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>
|
||
</dd></dl>
|
||
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="command-line-interface">
|
||
<span id="timeit-command-line-interface"></span><h2>命令行界面<a class="headerlink" href="#command-line-interface" title="永久链接至标题">¶</a></h2>
|
||
<p>从命令行调用程序时，使用以下表单:</p>
|
||
<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">h</span><span class="p">]</span> <span class="p">[</span><span class="n">statement</span> <span class="o">...</span><span class="p">]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果了解以下选项：</p>
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-n">
|
||
<code class="sig-name descname">-n</code><code class="sig-prename descclassname"> N</code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--number</code><code class="sig-prename descclassname">=N</code><a class="headerlink" href="#cmdoption-timeit-n" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>执行 '语句' 多少次</p>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-r">
|
||
<code class="sig-name descname">-r</code><code class="sig-prename descclassname"> N</code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--repeat</code><code class="sig-prename descclassname">=N</code><a class="headerlink" href="#cmdoption-timeit-r" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>重复计时器的次数（默认为5）</p>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-s">
|
||
<code class="sig-name descname">-s</code><code class="sig-prename descclassname"> S</code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--setup</code><code class="sig-prename descclassname">=S</code><a class="headerlink" href="#cmdoption-timeit-s" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>最初要执行一次的语句（默认为 <code class="docutils literal notranslate"><span class="pre">pass</span></code> ）</p>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-p">
|
||
<code class="sig-name descname">-p</code><code class="sig-prename descclassname"></code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--process</code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-timeit-p" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>测量进程时间，而不是 wallclock 时间，使用 <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> 而不是 <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> ，这是默认值</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.3 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-u">
|
||
<code class="sig-name descname">-u</code><code class="sig-prename descclassname"></code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--unit</code><code class="sig-prename descclassname">=U</code><a class="headerlink" href="#cmdoption-timeit-u" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>指定定时器输出的时间单位；可以选择 nsec，usec，msec或sec</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.5 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-v">
|
||
<code class="sig-name descname">-v</code><code class="sig-prename descclassname"></code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--verbose</code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-timeit-v" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>打印原始计时结果；重复更多位数精度</p>
|
||
</dd></dl>
|
||
|
||
<dl class="cmdoption">
|
||
<dt id="cmdoption-timeit-h">
|
||
<code class="sig-name descname">-h</code><code class="sig-prename descclassname"></code><code class="sig-prename descclassname">, </code><code class="sig-name descname">--help</code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-timeit-h" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>打印一条简短的使用信息并退出</p>
|
||
</dd></dl>
|
||
|
||
<p>可以通过将每一行指定为单独的语句参数来给出多行语句；通过在引号中包含参数并使用前导空格可以缩进行。多个 <a class="reference internal" href="#cmdoption-timeit-s"><code class="xref std std-option docutils literal notranslate"><span class="pre">-s</span></code></a> 选项的处理方式相似。</p>
|
||
<p>如果未给出 <a class="reference internal" href="#cmdoption-timeit-n"><code class="xref std std-option docutils literal notranslate"><span class="pre">-n</span></code></a>，则会通过尝试按序列 1, 2, 5, 10, 20, 50, ... 递增的数值来计算合适的循环次数，直到总计时间至少为 0.2 秒。</p>
|
||
<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> 测量可能受到在同一台机器上运行的其他程序的影响，因此在需要精确计时时最好的做法是重复几次计时并使用最佳时间。 <a class="reference internal" href="#cmdoption-timeit-r"><code class="xref std std-option docutils literal notranslate"><span class="pre">-r</span></code></a> 选项对此有利；在大多数情况下，默认的 5 次重复可能就足够了。 你可以使用 <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> 来测量CPU时间。</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>执行 pass 语句会产生一定的基线开销。这里的代码不会试图隐藏它，但你应该知道它。可以通过不带参数调用程序来测量基线开销，并且Python版本之间可能会有所不同。</p>
|
||
</div>
|
||
</section>
|
||
<section id="examples">
|
||
<span id="timeit-examples"></span><h2>例子<a class="headerlink" href="#examples" title="永久链接至标题">¶</a></h2>
|
||
<p>可以提供一个在开头只执行一次的 setup 语句：</p>
|
||
<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="s1">'text = "sample string"; char = "g"'</span><span class="w"> </span><span class="s1">'char in text'</span>
|
||
<span class="go">5000000 loops, best of 5: 0.0877 usec per loop</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="s1">'text = "sample string"; char = "g"'</span><span class="w"> </span><span class="s1">'text.find(char)'</span>
|
||
<span class="go">1000000 loops, best of 5: 0.342 usec per loop</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">timeit</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="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>
|
||
<span class="go">0.41440500499993504</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="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>
|
||
<span class="go">1.7246671520006203</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>使用 <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> 类及其方法可以完成同样的操作:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">timeit</span>
|
||
<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>
|
||
<span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">timeit</span><span class="p">()</span>
|
||
<span class="go">0.3955516149999312</span>
|
||
<span class="gp">>>> </span><span class="n">t</span><span class="o">.</span><span class="n">repeat</span><span class="p">()</span>
|
||
<span class="go">[0.40183617287970225, 0.37027556854118704, 0.38344867356679524, 0.3712595970846668, 0.37866875250654886]</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>以下示例显示如何计算包含多行的表达式。 在这里我们对比使用 <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> 与 <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> 的开销来测试缺失与提供对象属性:</p>
|
||
<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="s1">'try:'</span><span class="w"> </span><span class="s1">' str.__bool__'</span><span class="w"> </span><span class="s1">'except AttributeError:'</span><span class="w"> </span><span class="s1">' pass'</span>
|
||
<span class="go">20000 loops, best of 5: 15.7 usec per loop</span>
|
||
<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'if hasattr(str, "__bool__"): pass'</span>
|
||
<span class="go">50000 loops, best of 5: 4.26 usec per loop</span>
|
||
|
||
<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'try:'</span><span class="w"> </span><span class="s1">' int.__bool__'</span><span class="w"> </span><span class="s1">'except AttributeError:'</span><span class="w"> </span><span class="s1">' pass'</span>
|
||
<span class="go">200000 loops, best of 5: 1.43 usec per loop</span>
|
||
<span class="gp">$ </span>python<span class="w"> </span>-m<span class="w"> </span>timeit<span class="w"> </span><span class="s1">'if hasattr(int, "__bool__"): pass'</span>
|
||
<span class="go">100000 loops, best of 5: 2.23 usec per loop</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">timeit</span>
|
||
<span class="gp">>>> </span><span class="c1"># attribute is missing</span>
|
||
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"""</span><span class="se">\</span>
|
||
<span class="gp">... </span><span class="s2">try:</span>
|
||
<span class="gp">... </span><span class="s2"> str.__bool__</span>
|
||
<span class="gp">... </span><span class="s2">except AttributeError:</span>
|
||
<span class="gp">... </span><span class="s2"> pass</span>
|
||
<span class="gp">... </span><span class="s2">"""</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="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>
|
||
<span class="go">0.9138244460009446</span>
|
||
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"if hasattr(str, '__bool__'): pass"</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="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>
|
||
<span class="go">0.5829014980008651</span>
|
||
<span class="gp">>>></span>
|
||
<span class="gp">>>> </span><span class="c1"># attribute is present</span>
|
||
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"""</span><span class="se">\</span>
|
||
<span class="gp">... </span><span class="s2">try:</span>
|
||
<span class="gp">... </span><span class="s2"> int.__bool__</span>
|
||
<span class="gp">... </span><span class="s2">except AttributeError:</span>
|
||
<span class="gp">... </span><span class="s2"> pass</span>
|
||
<span class="gp">... </span><span class="s2">"""</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="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>
|
||
<span class="go">0.04215312199994514</span>
|
||
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="s2">"if hasattr(int, '__bool__'): pass"</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="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>
|
||
<span class="go">0.08588060699912603</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>要让 <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"><span class="pre">timeit</span></code></a> 模块访问你定义的函数，你可以传递一个包含 import 语句的 <em>setup</em> 参数:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">test</span><span class="p">():</span>
|
||
<span class="w"> </span><span class="sd">"""Stupid test function"""</span>
|
||
<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>
|
||
|
||
<span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
|
||
<span class="kn">import</span> <span class="nn">timeit</span>
|
||
<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>
|
||
</pre></div>
|
||
</div>
|
||
<p>另一种选择是将 <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> 传递给 <em>globals</em> 参数，这将导致代码在当前的全局命名空间中执行。这比单独指定 import 更方便</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">f</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span>
|
||
<span class="k">def</span> <span class="nf">g</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">4</span>
|
||
<span class="k">def</span> <span class="nf">h</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="n">x</span><span class="o">**</span><span class="mi">8</span>
|
||
|
||
<span class="kn">import</span> <span class="nn">timeit</span>
|
||
<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>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
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|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeit</span></code> --- 测量小代码片段的执行时间</a><ul>
|
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<li><a class="reference internal" href="#basic-examples">基本示例</a></li>
|
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