You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
329 lines
11 KiB
329 lines
11 KiB
:mod:`timeit` --- Measure execution time of small code snippets
|
|
===============================================================
|
|
|
|
.. module:: timeit
|
|
:synopsis: Measure the execution time of small code snippets.
|
|
|
|
|
|
.. versionadded:: 2.3
|
|
|
|
.. index::
|
|
single: Benchmarking
|
|
single: Performance
|
|
|
|
**Source code:** :source:`Lib/timeit.py`
|
|
|
|
--------------
|
|
|
|
This module provides a simple way to time small bits of Python code. It has both
|
|
a :ref:`timeit-command-line-interface` as well as a :ref:`callable <python-interface>`
|
|
one. It avoids a number of common traps for measuring execution times.
|
|
See also Tim Peters' introduction to the "Algorithms" chapter in the *Python
|
|
Cookbook*, published by O'Reilly.
|
|
|
|
|
|
Basic Examples
|
|
--------------
|
|
|
|
The following example shows how the :ref:`timeit-command-line-interface`
|
|
can be used to compare three different expressions:
|
|
|
|
.. code-block:: sh
|
|
|
|
$ python -m timeit '"-".join(str(n) for n in range(100))'
|
|
10000 loops, best of 3: 40.3 usec per loop
|
|
$ python -m timeit '"-".join([str(n) for n in range(100)])'
|
|
10000 loops, best of 3: 33.4 usec per loop
|
|
$ python -m timeit '"-".join(map(str, range(100)))'
|
|
10000 loops, best of 3: 25.2 usec per loop
|
|
|
|
This can be achieved from the :ref:`python-interface` with::
|
|
|
|
>>> import timeit
|
|
>>> timeit.timeit('"-".join(str(n) for n in range(100))', number=10000)
|
|
0.8187260627746582
|
|
>>> timeit.timeit('"-".join([str(n) for n in range(100)])', number=10000)
|
|
0.7288308143615723
|
|
>>> timeit.timeit('"-".join(map(str, range(100)))', number=10000)
|
|
0.5858950614929199
|
|
|
|
Note however that :mod:`timeit` will automatically determine the number of
|
|
repetitions only when the command-line interface is used. In the
|
|
:ref:`timeit-examples` section you can find more advanced examples.
|
|
|
|
|
|
.. _python-interface:
|
|
|
|
Python Interface
|
|
----------------
|
|
|
|
The module defines three convenience functions and a public class:
|
|
|
|
|
|
.. function:: timeit(stmt='pass', setup='pass', timer=<default timer>, number=1000000)
|
|
|
|
Create a :class:`Timer` instance with the given statement, *setup* code and
|
|
*timer* function and run its :meth:`.timeit` method with *number* executions.
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
.. function:: repeat(stmt='pass', setup='pass', timer=<default timer>, repeat=3, number=1000000)
|
|
|
|
Create a :class:`Timer` instance with the given statement, *setup* code and
|
|
*timer* function and run its :meth:`.repeat` method with the given *repeat*
|
|
count and *number* executions.
|
|
|
|
.. versionadded:: 2.6
|
|
|
|
|
|
.. function:: default_timer()
|
|
|
|
Define a default timer, in a platform-specific manner. On Windows,
|
|
:func:`time.clock` has microsecond granularity, but :func:`time.time`'s
|
|
granularity is 1/60th of a second. On Unix, :func:`time.clock` has 1/100th of
|
|
a second granularity, and :func:`time.time` is much more precise. On either
|
|
platform, :func:`default_timer` measures wall clock time, not the CPU
|
|
time. This means that other processes running on the same computer may
|
|
interfere with the timing.
|
|
|
|
|
|
.. class:: Timer(stmt='pass', setup='pass', timer=<timer function>)
|
|
|
|
Class for timing execution speed of small code snippets.
|
|
|
|
The constructor takes a statement to be timed, an additional statement used
|
|
for setup, and a timer function. Both statements default to ``'pass'``;
|
|
the timer function is platform-dependent (see the module doc string).
|
|
*stmt* and *setup* may also contain multiple statements separated by ``;``
|
|
or newlines, as long as they don't contain multi-line string literals.
|
|
|
|
To measure the execution time of the first statement, use the :meth:`.timeit`
|
|
method. The :meth:`.repeat` method is a convenience to call :meth:`.timeit`
|
|
multiple times and return a list of results.
|
|
|
|
.. versionchanged:: 2.6
|
|
The *stmt* and *setup* parameters can now also take objects that are
|
|
callable without arguments. This will embed calls to them in a timer
|
|
function that will then be executed by :meth:`.timeit`. Note that the
|
|
timing overhead is a little larger in this case because of the extra
|
|
function calls.
|
|
|
|
|
|
.. method:: Timer.timeit(number=1000000)
|
|
|
|
Time *number* executions of the main statement. This executes the setup
|
|
statement once, and then returns the time it takes to execute the main
|
|
statement a number of times, measured in seconds as a float.
|
|
The argument is the number of times through the loop, defaulting to one
|
|
million. The main statement, the setup statement and the timer function
|
|
to be used are passed to the constructor.
|
|
|
|
.. note::
|
|
|
|
By default, :meth:`.timeit` temporarily turns off :term:`garbage
|
|
collection` during the timing. The advantage of this approach is that
|
|
it makes independent timings more comparable. This disadvantage is
|
|
that GC may be an important component of the performance of the
|
|
function being measured. If so, GC can be re-enabled as the first
|
|
statement in the *setup* string. For example::
|
|
|
|
timeit.Timer('for i in xrange(10): oct(i)', 'gc.enable()').timeit()
|
|
|
|
|
|
.. method:: Timer.repeat(repeat=3, number=1000000)
|
|
|
|
Call :meth:`.timeit` a few times.
|
|
|
|
This is a convenience function that calls the :meth:`.timeit` repeatedly,
|
|
returning a list of results. The first argument specifies how many times
|
|
to call :meth:`.timeit`. The second argument specifies the *number*
|
|
argument for :meth:`.timeit`.
|
|
|
|
.. note::
|
|
|
|
It's tempting to calculate mean and standard deviation from the result
|
|
vector and report these. However, this is not very useful.
|
|
In a typical case, the lowest value gives a lower bound for how fast
|
|
your machine can run the given code snippet; higher values in the
|
|
result vector are typically not caused by variability in Python's
|
|
speed, but by other processes interfering with your timing accuracy.
|
|
So the :func:`min` of the result is probably the only number you
|
|
should be interested in. After that, you should look at the entire
|
|
vector and apply common sense rather than statistics.
|
|
|
|
|
|
.. method:: Timer.print_exc(file=None)
|
|
|
|
Helper to print a traceback from the timed code.
|
|
|
|
Typical use::
|
|
|
|
t = Timer(...) # outside the try/except
|
|
try:
|
|
t.timeit(...) # or t.repeat(...)
|
|
except:
|
|
t.print_exc()
|
|
|
|
The advantage over the standard traceback is that source lines in the
|
|
compiled template will be displayed. The optional *file* argument directs
|
|
where the traceback is sent; it defaults to :data:`sys.stderr`.
|
|
|
|
|
|
.. _timeit-command-line-interface:
|
|
|
|
Command-Line Interface
|
|
----------------------
|
|
|
|
When called as a program from the command line, the following form is used::
|
|
|
|
python -m timeit [-n N] [-r N] [-s S] [-t] [-c] [-h] [statement ...]
|
|
|
|
Where the following options are understood:
|
|
|
|
.. program:: timeit
|
|
|
|
.. cmdoption:: -n N, --number=N
|
|
|
|
how many times to execute 'statement'
|
|
|
|
.. cmdoption:: -r N, --repeat=N
|
|
|
|
how many times to repeat the timer (default 3)
|
|
|
|
.. cmdoption:: -s S, --setup=S
|
|
|
|
statement to be executed once initially (default ``pass``)
|
|
|
|
.. cmdoption:: -t, --time
|
|
|
|
use :func:`time.time` (default on all platforms but Windows)
|
|
|
|
.. cmdoption:: -c, --clock
|
|
|
|
use :func:`time.clock` (default on Windows)
|
|
|
|
.. cmdoption:: -v, --verbose
|
|
|
|
print raw timing results; repeat for more digits precision
|
|
|
|
.. cmdoption:: -h, --help
|
|
|
|
print a short usage message and exit
|
|
|
|
A multi-line statement may be given by specifying each line as a separate
|
|
statement argument; indented lines are possible by enclosing an argument in
|
|
quotes and using leading spaces. Multiple :option:`-s` options are treated
|
|
similarly.
|
|
|
|
If :option:`-n` is not given, a suitable number of loops is calculated by trying
|
|
successive powers of 10 until the total time is at least 0.2 seconds.
|
|
|
|
:func:`default_timer` measurations can be affected by other programs running on
|
|
the same machine, so
|
|
the best thing to do when accurate timing is necessary is to repeat
|
|
the timing a few times and use the best time. The :option:`-r` option is good
|
|
for this; the default of 3 repetitions is probably enough in most cases. On
|
|
Unix, you can use :func:`time.clock` to measure CPU time.
|
|
|
|
.. note::
|
|
|
|
There is a certain baseline overhead associated with executing a pass statement.
|
|
The code here doesn't try to hide it, but you should be aware of it. The
|
|
baseline overhead can be measured by invoking the program without arguments, and
|
|
it might differ between Python versions. Also, to fairly compare older Python
|
|
versions to Python 2.3, you may want to use Python's :option:`!-O`
|
|
option (see :ref:`Optimizations <using-on-optimizations>`) for
|
|
the older versions to avoid timing ``SET_LINENO`` instructions.
|
|
|
|
|
|
.. _timeit-examples:
|
|
|
|
Examples
|
|
--------
|
|
|
|
It is possible to provide a setup statement that is executed only once at the beginning:
|
|
|
|
.. code-block:: sh
|
|
|
|
$ python -m timeit -s 'text = "sample string"; char = "g"' 'char in text'
|
|
10000000 loops, best of 3: 0.0877 usec per loop
|
|
$ python -m timeit -s 'text = "sample string"; char = "g"' 'text.find(char)'
|
|
1000000 loops, best of 3: 0.342 usec per loop
|
|
|
|
::
|
|
|
|
>>> import timeit
|
|
>>> timeit.timeit('char in text', setup='text = "sample string"; char = "g"')
|
|
0.41440500499993504
|
|
>>> timeit.timeit('text.find(char)', setup='text = "sample string"; char = "g"')
|
|
1.7246671520006203
|
|
|
|
The same can be done using the :class:`Timer` class and its methods::
|
|
|
|
>>> import timeit
|
|
>>> t = timeit.Timer('char in text', setup='text = "sample string"; char = "g"')
|
|
>>> t.timeit()
|
|
0.3955516149999312
|
|
>>> t.repeat()
|
|
[0.40193588800002544, 0.3960157959998014, 0.39594301399984033]
|
|
|
|
|
|
The following examples show how to time expressions that contain multiple lines.
|
|
Here we compare the cost of using :func:`hasattr` vs. :keyword:`try`/:keyword:`except`
|
|
to test for missing and present object attributes:
|
|
|
|
.. code-block:: sh
|
|
|
|
$ python -m timeit 'try:' ' str.__nonzero__' 'except AttributeError:' ' pass'
|
|
100000 loops, best of 3: 15.7 usec per loop
|
|
$ python -m timeit 'if hasattr(str, "__nonzero__"): pass'
|
|
100000 loops, best of 3: 4.26 usec per loop
|
|
|
|
$ python -m timeit 'try:' ' int.__nonzero__' 'except AttributeError:' ' pass'
|
|
1000000 loops, best of 3: 1.43 usec per loop
|
|
$ python -m timeit 'if hasattr(int, "__nonzero__"): pass'
|
|
100000 loops, best of 3: 2.23 usec per loop
|
|
|
|
::
|
|
|
|
>>> import timeit
|
|
>>> # attribute is missing
|
|
>>> s = """\
|
|
... try:
|
|
... str.__nonzero__
|
|
... except AttributeError:
|
|
... pass
|
|
... """
|
|
>>> timeit.timeit(stmt=s, number=100000)
|
|
0.9138244460009446
|
|
>>> s = "if hasattr(str, '__bool__'): pass"
|
|
>>> timeit.timeit(stmt=s, number=100000)
|
|
0.5829014980008651
|
|
>>>
|
|
>>> # attribute is present
|
|
>>> s = """\
|
|
... try:
|
|
... int.__nonzero__
|
|
... except AttributeError:
|
|
... pass
|
|
... """
|
|
>>> timeit.timeit(stmt=s, number=100000)
|
|
0.04215312199994514
|
|
>>> s = "if hasattr(int, '__bool__'): pass"
|
|
>>> timeit.timeit(stmt=s, number=100000)
|
|
0.08588060699912603
|
|
|
|
To give the :mod:`timeit` module access to functions you define, you can pass a
|
|
*setup* parameter which contains an import statement::
|
|
|
|
def test():
|
|
"""Stupid test function"""
|
|
L = []
|
|
for i in range(100):
|
|
L.append(i)
|
|
|
|
if __name__ == '__main__':
|
|
import timeit
|
|
print(timeit.timeit("test()", setup="from __main__ import test"))
|