Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 1 | :mod:`timeit` --- Measure execution time of small code snippets |
| 2 | =============================================================== |
| 3 | |
| 4 | .. module:: timeit |
| 5 | :synopsis: Measure the execution time of small code snippets. |
| 6 | |
Terry Jan Reedy | fa089b9 | 2016-06-11 15:02:54 -0400 | [diff] [blame] | 7 | **Source code:** :source:`Lib/timeit.py` |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 8 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 9 | .. index:: |
| 10 | single: Benchmarking |
| 11 | single: Performance |
| 12 | |
Raymond Hettinger | a199368 | 2011-01-27 01:20:32 +0000 | [diff] [blame] | 13 | -------------- |
| 14 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 15 | This module provides a simple way to time small bits of Python code. It has both |
Martin Panter | 00ccacc | 2016-04-16 04:59:38 +0000 | [diff] [blame] | 16 | a :ref:`timeit-command-line-interface` as well as a :ref:`callable <python-interface>` |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 17 | one. It avoids a number of common traps for measuring execution times. |
| 18 | See also Tim Peters' introduction to the "Algorithms" chapter in the *Python |
| 19 | Cookbook*, published by O'Reilly. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 20 | |
| 21 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 22 | Basic Examples |
| 23 | -------------- |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 24 | |
Martin Panter | 00ccacc | 2016-04-16 04:59:38 +0000 | [diff] [blame] | 25 | The following example shows how the :ref:`timeit-command-line-interface` |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 26 | can be used to compare three different expressions: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 27 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 28 | .. code-block:: sh |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 29 | |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 30 | $ python3 -m timeit '"-".join(str(n) for n in range(100))' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 31 | 10000 loops, best of 5: 30.2 usec per loop |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 32 | $ python3 -m timeit '"-".join([str(n) for n in range(100)])' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 33 | 10000 loops, best of 5: 27.5 usec per loop |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 34 | $ python3 -m timeit '"-".join(map(str, range(100)))' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 35 | 10000 loops, best of 5: 23.2 usec per loop |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 36 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 37 | This can be achieved from the :ref:`python-interface` with:: |
| 38 | |
| 39 | >>> import timeit |
| 40 | >>> timeit.timeit('"-".join(str(n) for n in range(100))', number=10000) |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 41 | 0.3018611848820001 |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 42 | >>> timeit.timeit('"-".join([str(n) for n in range(100)])', number=10000) |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 43 | 0.2727368790656328 |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 44 | >>> timeit.timeit('"-".join(map(str, range(100)))', number=10000) |
Ezio Melotti | 591176e | 2014-08-04 17:01:16 +0300 | [diff] [blame] | 45 | 0.23702679807320237 |
| 46 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 47 | |
| 48 | Note however that :mod:`timeit` will automatically determine the number of |
| 49 | repetitions only when the command-line interface is used. In the |
| 50 | :ref:`timeit-examples` section you can find more advanced examples. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 51 | |
| 52 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 53 | .. _python-interface: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 54 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 55 | Python Interface |
| 56 | ---------------- |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 57 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 58 | The module defines three convenience functions and a public class: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 59 | |
| 60 | |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 61 | .. function:: timeit(stmt='pass', setup='pass', timer=<default timer>, number=1000000, globals=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 62 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 63 | Create a :class:`Timer` instance with the given statement, *setup* code and |
| 64 | *timer* function and run its :meth:`.timeit` method with *number* executions. |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 65 | The optional *globals* argument specifies a namespace in which to execute the |
| 66 | code. |
| 67 | |
| 68 | .. versionchanged:: 3.5 |
| 69 | The optional *globals* parameter was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 70 | |
| 71 | |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 72 | .. function:: repeat(stmt='pass', setup='pass', timer=<default timer>, repeat=3, number=1000000, globals=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 73 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 74 | Create a :class:`Timer` instance with the given statement, *setup* code and |
| 75 | *timer* function and run its :meth:`.repeat` method with the given *repeat* |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 76 | count and *number* executions. The optional *globals* argument specifies a |
| 77 | namespace in which to execute the code. |
Sandro Tosi | e6c3462 | 2012-04-24 18:11:46 +0200 | [diff] [blame] | 78 | |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 79 | .. versionchanged:: 3.5 |
| 80 | The optional *globals* parameter was added. |
Sandro Tosi | e6c3462 | 2012-04-24 18:11:46 +0200 | [diff] [blame] | 81 | |
| 82 | .. function:: default_timer() |
| 83 | |
Georg Brandl | 67c1444 | 2012-05-01 11:59:36 +0200 | [diff] [blame] | 84 | The default timer, which is always :func:`time.perf_counter`. |
Sandro Tosi | e6c3462 | 2012-04-24 18:11:46 +0200 | [diff] [blame] | 85 | |
Ezio Melotti | 4443762 | 2012-10-02 06:01:16 +0300 | [diff] [blame] | 86 | .. versionchanged:: 3.3 |
| 87 | :func:`time.perf_counter` is now the default timer. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 88 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 89 | |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 90 | .. class:: Timer(stmt='pass', setup='pass', timer=<timer function>, globals=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 91 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 92 | Class for timing execution speed of small code snippets. |
| 93 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 94 | The constructor takes a statement to be timed, an additional statement used |
| 95 | for setup, and a timer function. Both statements default to ``'pass'``; |
| 96 | the timer function is platform-dependent (see the module doc string). |
| 97 | *stmt* and *setup* may also contain multiple statements separated by ``;`` |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 98 | or newlines, as long as they don't contain multi-line string literals. The |
| 99 | statement will by default be executed within timeit's namespace; this behavior |
| 100 | can be controlled by passing a namespace to *globals*. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 101 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 102 | To measure the execution time of the first statement, use the :meth:`.timeit` |
Steven D'Aprano | 09f4f71 | 2016-08-15 01:27:03 +1000 | [diff] [blame] | 103 | method. The :meth:`.repeat` and :meth:`.autorange` methods are convenience |
| 104 | methods to call :meth:`.timeit` multiple times. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 105 | |
Andrew Kuchling | 333518e | 2015-04-21 19:43:33 -0400 | [diff] [blame] | 106 | The execution time of *setup* is excluded from the overall timed execution run. |
| 107 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 108 | The *stmt* and *setup* parameters can also take objects that are callable |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 109 | without arguments. This will embed calls to them in a timer function that |
Ezio Melotti | a3ccb23 | 2012-09-20 06:13:38 +0300 | [diff] [blame] | 110 | will then be executed by :meth:`.timeit`. Note that the timing overhead is a |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 111 | little larger in this case because of the extra function calls. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 112 | |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 113 | .. versionchanged:: 3.5 |
| 114 | The optional *globals* parameter was added. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 115 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 116 | .. method:: Timer.timeit(number=1000000) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 117 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 118 | Time *number* executions of the main statement. This executes the setup |
| 119 | statement once, and then returns the time it takes to execute the main |
| 120 | statement a number of times, measured in seconds as a float. |
| 121 | The argument is the number of times through the loop, defaulting to one |
| 122 | million. The main statement, the setup statement and the timer function |
| 123 | to be used are passed to the constructor. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 124 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 125 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 126 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 127 | By default, :meth:`.timeit` temporarily turns off :term:`garbage |
| 128 | collection` during the timing. The advantage of this approach is that |
| 129 | it makes independent timings more comparable. This disadvantage is |
| 130 | that GC may be an important component of the performance of the |
| 131 | function being measured. If so, GC can be re-enabled as the first |
| 132 | statement in the *setup* string. For example:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 133 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 134 | timeit.Timer('for i in range(10): oct(i)', 'gc.enable()').timeit() |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 135 | |
| 136 | |
Steven D'Aprano | 09f4f71 | 2016-08-15 01:27:03 +1000 | [diff] [blame] | 137 | .. method:: Timer.autorange(callback=None) |
| 138 | |
| 139 | Automatically determine how many times to call :meth:`.timeit`. |
| 140 | |
| 141 | This is a convenience function that calls :meth:`.timeit` repeatedly |
| 142 | so that the total time >= 0.2 second, returning the eventual |
| 143 | (number of loops, time taken for that number of loops). It calls |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 144 | :meth:`.timeit` with increasing numbers from the sequence 1, 2, 5, |
| 145 | 10, 20, 50, ... until the time taken is at least 0.2 second. |
Steven D'Aprano | 09f4f71 | 2016-08-15 01:27:03 +1000 | [diff] [blame] | 146 | |
Serhiy Storchaka | 989db5c | 2016-10-19 16:37:13 +0300 | [diff] [blame] | 147 | If *callback* is given and is not ``None``, it will be called after |
Steven D'Aprano | 09f4f71 | 2016-08-15 01:27:03 +1000 | [diff] [blame] | 148 | each trial with two arguments: ``callback(number, time_taken)``. |
| 149 | |
Steven D'Aprano | a0d3eef | 2016-08-15 02:47:49 +1000 | [diff] [blame] | 150 | .. versionadded:: 3.6 |
| 151 | |
Steven D'Aprano | 09f4f71 | 2016-08-15 01:27:03 +1000 | [diff] [blame] | 152 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 153 | .. method:: Timer.repeat(repeat=3, number=1000000) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 154 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 155 | Call :meth:`.timeit` a few times. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 156 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 157 | This is a convenience function that calls the :meth:`.timeit` repeatedly, |
| 158 | returning a list of results. The first argument specifies how many times |
| 159 | to call :meth:`.timeit`. The second argument specifies the *number* |
| 160 | argument for :meth:`.timeit`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 161 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 162 | .. note:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 163 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 164 | It's tempting to calculate mean and standard deviation from the result |
| 165 | vector and report these. However, this is not very useful. |
| 166 | In a typical case, the lowest value gives a lower bound for how fast |
| 167 | your machine can run the given code snippet; higher values in the |
| 168 | result vector are typically not caused by variability in Python's |
| 169 | speed, but by other processes interfering with your timing accuracy. |
| 170 | So the :func:`min` of the result is probably the only number you |
| 171 | should be interested in. After that, you should look at the entire |
| 172 | vector and apply common sense rather than statistics. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 173 | |
| 174 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 175 | .. method:: Timer.print_exc(file=None) |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 176 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 177 | Helper to print a traceback from the timed code. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 178 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 179 | Typical use:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 180 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 181 | t = Timer(...) # outside the try/except |
| 182 | try: |
| 183 | t.timeit(...) # or t.repeat(...) |
Andrew Svetlov | 4739561 | 2012-11-02 22:07:26 +0200 | [diff] [blame] | 184 | except Exception: |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 185 | t.print_exc() |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 186 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 187 | The advantage over the standard traceback is that source lines in the |
| 188 | compiled template will be displayed. The optional *file* argument directs |
| 189 | where the traceback is sent; it defaults to :data:`sys.stderr`. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 190 | |
| 191 | |
Martin Panter | 00ccacc | 2016-04-16 04:59:38 +0000 | [diff] [blame] | 192 | .. _timeit-command-line-interface: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 193 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 194 | Command-Line Interface |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 195 | ---------------------- |
| 196 | |
| 197 | When called as a program from the command line, the following form is used:: |
| 198 | |
Victor Stinner | 3d7feb9 | 2016-10-18 17:18:21 +0200 | [diff] [blame] | 199 | python -m timeit [-n N] [-r N] [-u U] [-s S] [-h] [statement ...] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 200 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 201 | Where the following options are understood: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 202 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 203 | .. program:: timeit |
| 204 | |
| 205 | .. cmdoption:: -n N, --number=N |
| 206 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 207 | how many times to execute 'statement' |
| 208 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 209 | .. cmdoption:: -r N, --repeat=N |
| 210 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 211 | how many times to repeat the timer (default 3) |
| 212 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 213 | .. cmdoption:: -s S, --setup=S |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 214 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 215 | statement to be executed once initially (default ``pass``) |
| 216 | |
Georg Brandl | 67c1444 | 2012-05-01 11:59:36 +0200 | [diff] [blame] | 217 | .. cmdoption:: -p, --process |
| 218 | |
| 219 | measure process time, not wallclock time, using :func:`time.process_time` |
| 220 | instead of :func:`time.perf_counter`, which is the default |
| 221 | |
| 222 | .. versionadded:: 3.3 |
| 223 | |
Robert Collins | 302dbc6 | 2015-03-18 09:54:50 +1300 | [diff] [blame] | 224 | .. cmdoption:: -u, --unit=U |
| 225 | |
Victor Stinner | c3e40f8 | 2016-10-18 17:42:48 +0200 | [diff] [blame] | 226 | specify a time unit for timer output; can select nsec, usec, msec, or sec |
Robert Collins | 302dbc6 | 2015-03-18 09:54:50 +1300 | [diff] [blame] | 227 | |
| 228 | .. versionadded:: 3.5 |
| 229 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 230 | .. cmdoption:: -v, --verbose |
| 231 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 232 | print raw timing results; repeat for more digits precision |
| 233 | |
Éric Araujo | 713d303 | 2010-11-18 16:38:46 +0000 | [diff] [blame] | 234 | .. cmdoption:: -h, --help |
| 235 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 236 | print a short usage message and exit |
| 237 | |
| 238 | A multi-line statement may be given by specifying each line as a separate |
| 239 | statement argument; indented lines are possible by enclosing an argument in |
| 240 | quotes and using leading spaces. Multiple :option:`-s` options are treated |
| 241 | similarly. |
| 242 | |
| 243 | If :option:`-n` is not given, a suitable number of loops is calculated by trying |
| 244 | successive powers of 10 until the total time is at least 0.2 seconds. |
| 245 | |
Georg Brandl | 67c1444 | 2012-05-01 11:59:36 +0200 | [diff] [blame] | 246 | :func:`default_timer` measurements can be affected by other programs running on |
| 247 | the same machine, so the best thing to do when accurate timing is necessary is |
| 248 | to repeat the timing a few times and use the best time. The :option:`-r` |
| 249 | option is good for this; the default of 3 repetitions is probably enough in |
| 250 | most cases. You can use :func:`time.process_time` to measure CPU time. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 251 | |
| 252 | .. note:: |
| 253 | |
| 254 | There is a certain baseline overhead associated with executing a pass statement. |
| 255 | The code here doesn't try to hide it, but you should be aware of it. The |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 256 | baseline overhead can be measured by invoking the program without arguments, |
| 257 | and it might differ between Python versions. |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 258 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 259 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 260 | .. _timeit-examples: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 261 | |
| 262 | Examples |
| 263 | -------- |
| 264 | |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 265 | It is possible to provide a setup statement that is executed only once at the beginning: |
| 266 | |
| 267 | .. code-block:: sh |
| 268 | |
| 269 | $ python -m timeit -s 'text = "sample string"; char = "g"' 'char in text' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 270 | 5000000 loops, best of 5: 0.0877 usec per loop |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 271 | $ python -m timeit -s 'text = "sample string"; char = "g"' 'text.find(char)' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 272 | 1000000 loops, best of 5: 0.342 usec per loop |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 273 | |
| 274 | :: |
| 275 | |
| 276 | >>> import timeit |
| 277 | >>> timeit.timeit('char in text', setup='text = "sample string"; char = "g"') |
| 278 | 0.41440500499993504 |
| 279 | >>> timeit.timeit('text.find(char)', setup='text = "sample string"; char = "g"') |
| 280 | 1.7246671520006203 |
| 281 | |
| 282 | The same can be done using the :class:`Timer` class and its methods:: |
| 283 | |
| 284 | >>> import timeit |
| 285 | >>> t = timeit.Timer('char in text', setup='text = "sample string"; char = "g"') |
| 286 | >>> t.timeit() |
| 287 | 0.3955516149999312 |
| 288 | >>> t.repeat() |
| 289 | [0.40193588800002544, 0.3960157959998014, 0.39594301399984033] |
| 290 | |
| 291 | |
| 292 | The following examples show how to time expressions that contain multiple lines. |
| 293 | Here we compare the cost of using :func:`hasattr` vs. :keyword:`try`/:keyword:`except` |
| 294 | to test for missing and present object attributes: |
| 295 | |
| 296 | .. code-block:: sh |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 297 | |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 298 | $ python -m timeit 'try:' ' str.__bool__' 'except AttributeError:' ' pass' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 299 | 20000 loops, best of 5: 15.7 usec per loop |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 300 | $ python -m timeit 'if hasattr(str, "__bool__"): pass' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 301 | 50000 loops, best of 5: 4.26 usec per loop |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 302 | |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 303 | $ python -m timeit 'try:' ' int.__bool__' 'except AttributeError:' ' pass' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 304 | 200000 loops, best of 5: 1.43 usec per loop |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 305 | $ python -m timeit 'if hasattr(int, "__bool__"): pass' |
Serhiy Storchaka | d3ff784 | 2016-10-23 15:17:05 +0300 | [diff] [blame^] | 306 | 100000 loops, best of 5: 2.23 usec per loop |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 307 | |
| 308 | :: |
| 309 | |
| 310 | >>> import timeit |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 311 | >>> # attribute is missing |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 312 | >>> s = """\ |
| 313 | ... try: |
| 314 | ... str.__bool__ |
| 315 | ... except AttributeError: |
| 316 | ... pass |
| 317 | ... """ |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 318 | >>> timeit.timeit(stmt=s, number=100000) |
| 319 | 0.9138244460009446 |
| 320 | >>> s = "if hasattr(str, '__bool__'): pass" |
| 321 | >>> timeit.timeit(stmt=s, number=100000) |
| 322 | 0.5829014980008651 |
| 323 | >>> |
| 324 | >>> # attribute is present |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 325 | >>> s = """\ |
| 326 | ... try: |
| 327 | ... int.__bool__ |
| 328 | ... except AttributeError: |
| 329 | ... pass |
| 330 | ... """ |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 331 | >>> timeit.timeit(stmt=s, number=100000) |
| 332 | 0.04215312199994514 |
| 333 | >>> s = "if hasattr(int, '__bool__'): pass" |
| 334 | >>> timeit.timeit(stmt=s, number=100000) |
| 335 | 0.08588060699912603 |
| 336 | |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 337 | |
| 338 | To give the :mod:`timeit` module access to functions you define, you can pass a |
Ezio Melotti | a3ccb23 | 2012-09-20 06:13:38 +0300 | [diff] [blame] | 339 | *setup* parameter which contains an import statement:: |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 340 | |
| 341 | def test(): |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 342 | """Stupid test function""" |
Collin Winter | c79461b | 2007-09-01 23:34:30 +0000 | [diff] [blame] | 343 | L = [i for i in range(100)] |
Georg Brandl | 116aa62 | 2007-08-15 14:28:22 +0000 | [diff] [blame] | 344 | |
Senthil Kumaran | 2e01535 | 2011-08-06 13:37:04 +0800 | [diff] [blame] | 345 | if __name__ == '__main__': |
Ezio Melotti | d0fe3e5 | 2012-10-02 05:35:39 +0300 | [diff] [blame] | 346 | import timeit |
| 347 | print(timeit.timeit("test()", setup="from __main__ import test")) |
Antoine Pitrou | ef3b9ed | 2014-08-22 23:13:50 -0400 | [diff] [blame] | 348 | |
| 349 | Another option is to pass :func:`globals` to the *globals* parameter, which will cause the code |
| 350 | to be executed within your current global namespace. This can be more convenient |
| 351 | than individually specifying imports:: |
| 352 | |
| 353 | def f(x): |
| 354 | return x**2 |
| 355 | def g(x): |
| 356 | return x**4 |
| 357 | def h(x): |
| 358 | return x**8 |
| 359 | |
| 360 | import timeit |
| 361 | print(timeit.timeit('[func(42) for func in (f,g,h)]', globals=globals())) |