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16 | <title>10.10 timeit -- Measure execution time of small code snippets</title> | |
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54 | <H1><A NAME="SECTION00121000000000000000000"> | |
55 | 10.10 <tt class="module">timeit</tt> -- | |
56 | Measure execution time of small code snippets</A> | |
57 | </H1> | |
58 | ||
59 | <P> | |
60 | <A NAME="module-timeit"></A> | |
61 | ||
62 | <P> | |
63 | ||
64 | <span class="versionnote">New in version 2.3.</span> | |
65 | ||
66 | <a id='l2h-3138' xml:id='l2h-3138'></a> | |
67 | ||
68 | <P> | |
69 | This module provides a simple way to time small bits of Python code. | |
70 | It has both command line as well as callable interfaces. It avoids a | |
71 | number of common traps for measuring execution times. See also Tim | |
72 | Peters' introduction to the ``Algorithms'' chapter in the | |
73 | <em class="citetitle" | |
74 | >Python Cookbook</em>, published by O'Reilly. | |
75 | ||
76 | <P> | |
77 | The module defines the following public class: | |
78 | ||
79 | <P> | |
80 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
81 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-3134' xml:id='l2h-3134' class="class">Timer</tt></b>(</nobr></td> | |
82 | <td><var></var><big>[</big><var>stmt=<code>'pass'</code> | |
83 | </var><big>[</big><var>, setup=<code>'pass'</code> | |
84 | </var><big>[</big><var>, timer=<timer function></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
85 | <dd> | |
86 | Class for timing execution speed of small code snippets. | |
87 | ||
88 | <P> | |
89 | The constructor takes a statement to be timed, an additional statement | |
90 | used for setup, and a timer function. Both statements default to | |
91 | <code>'pass'</code>; the timer function is platform-dependent (see the | |
92 | module doc string). The statements may contain newlines, as long as | |
93 | they don't contain multi-line string literals. | |
94 | ||
95 | <P> | |
96 | To measure the execution time of the first statement, use the | |
97 | <tt class="method">timeit()</tt> method. The <tt class="method">repeat()</tt> method is a | |
98 | convenience to call <tt class="method">timeit()</tt> multiple times and return a list | |
99 | of results. | |
100 | </dl> | |
101 | ||
102 | <P> | |
103 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
104 | <td><nobr><b><tt id='l2h-3135' xml:id='l2h-3135' class="method">print_exc</tt></b>(</nobr></td> | |
105 | <td><var></var><big>[</big><var>file=<tt class="constant">None</tt></var><big>]</big><var></var>)</td></tr></table></dt> | |
106 | <dd> | |
107 | Helper to print a traceback from the timed code. | |
108 | ||
109 | <P> | |
110 | Typical use: | |
111 | ||
112 | <P> | |
113 | <div class="verbatim"><pre> | |
114 | t = Timer(...) # outside the try/except | |
115 | try: | |
116 | t.timeit(...) # or t.repeat(...) | |
117 | except: | |
118 | t.print_exc() | |
119 | </pre></div> | |
120 | ||
121 | <P> | |
122 | The advantage over the standard traceback is that source lines in the | |
123 | compiled template will be displayed. | |
124 | The optional <var>file</var> argument directs where the traceback is sent; | |
125 | it defaults to <code>sys.stderr</code>. | |
126 | </dl> | |
127 | ||
128 | <P> | |
129 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
130 | <td><nobr><b><tt id='l2h-3136' xml:id='l2h-3136' class="method">repeat</tt></b>(</nobr></td> | |
131 | <td><var></var><big>[</big><var>repeat<code>=3</code> </var><big>[</big><var>, | |
132 | number<code>=1000000</code></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> | |
133 | <dd> | |
134 | Call <tt class="method">timeit()</tt> a few times. | |
135 | ||
136 | <P> | |
137 | This is a convenience function that calls the <tt class="method">timeit()</tt> | |
138 | repeatedly, returning a list of results. The first argument specifies | |
139 | how many times to call <tt class="method">timeit()</tt>. The second argument | |
140 | specifies the <var>number</var> argument for <tt class="function">timeit()</tt>. | |
141 | ||
142 | <P> | |
143 | <div class="note"><b class="label">Note:</b> | |
144 | It's tempting to calculate mean and standard deviation from the result | |
145 | vector and report these. However, this is not very useful. In a typical | |
146 | case, the lowest value gives a lower bound for how fast your machine can run | |
147 | the given code snippet; higher values in the result vector are typically not | |
148 | caused by variability in Python's speed, but by other processes interfering | |
149 | with your timing accuracy. So the <tt class="function">min()</tt> of the result is | |
150 | probably the only number you should be interested in. After that, you | |
151 | should look at the entire vector and apply common sense rather than | |
152 | statistics. | |
153 | </div> | |
154 | </dl> | |
155 | ||
156 | <P> | |
157 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> | |
158 | <td><nobr><b><tt id='l2h-3137' xml:id='l2h-3137' class="method">timeit</tt></b>(</nobr></td> | |
159 | <td><var></var><big>[</big><var>number<code>=1000000</code></var><big>]</big><var></var>)</td></tr></table></dt> | |
160 | <dd> | |
161 | Time <var>number</var> executions of the main statement. | |
162 | This executes the setup statement once, and then | |
163 | returns the time it takes to execute the main statement a number of | |
164 | times, measured in seconds as a float. The argument is the number of | |
165 | times through the loop, defaulting to one million. The main | |
166 | statement, the setup statement and the timer function to be used are | |
167 | passed to the constructor. | |
168 | ||
169 | <P> | |
170 | <div class="note"><b class="label">Note:</b> | |
171 | By default, <tt class="method">timeit()</tt> temporarily turns off garbage collection | |
172 | during the timing. The advantage of this approach is that it makes | |
173 | independent timings more comparable. This disadvantage is that GC | |
174 | may be an important component of the performance of the function being | |
175 | measured. If so, GC can be re-enabled as the first statement in the | |
176 | <var>setup</var> string. For example: | |
177 | <div class="verbatim"><pre> | |
178 | timeit.Timer('for i in xrange(10): oct(i)', 'gc.enable()').timeit() | |
179 | </pre></div> | |
180 | </div> | |
181 | </dl> | |
182 | ||
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