timeit --- Measure execution time of small code snippetsNew in version 2.3.
Source code: Lib/timeit.py
[UNKNOWN NODE transition]This module provides a simple way to time small bits of Python code. It has both a Command-Line Interface as well as a callable 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.
The following example shows how the Command-Line Interface can be used to compare three different expressions:
$ 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 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 timeit will automatically determine the number of
repetitions only when the command-line interface is used. In the
Examples section you can find more advanced examples.
The module defines three convenience functions and a public class:
timeit.timeit(stmt='pass', setup='pass', timer=<default timer>, number=1000000)[source]
Create a Timer instance with the given statement, setup code and
timer function and run its timeit() method with number executions.
New in version 2.6.
timeit.repeat(stmt='pass', setup='pass', timer=<default timer>, repeat=3, number=1000000)[source]
Create a Timer instance with the given statement, setup code and
timer function and run its repeat() method with the given repeat
count and number executions.
New in version 2.6.
timeit.default_timer()
Define a default timer, in a platform-specific manner. On Windows,
time.clock() has microsecond granularity, but time.time()'s
granularity is 1/60th of a second. On Unix, time.clock() has 1/100th of
a second granularity, and time.time() is much more precise. On either
platform, 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 timeit.Timer(stmt='pass', setup='pass', timer=<timer function>)[source]
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 timeit()
method. The repeat() method is a convenience to call timeit()
multiple times and return a list of results.
Changed in version 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 timeit(). Note that the
timing overhead is a little larger in this case because of the extra
function calls.
timeit(number=1000000)[source]
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, timeit() temporarily turns off 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()
repeat(repeat=3, number=1000000)[source]
Call timeit() a few times.
This is a convenience function that calls the timeit() repeatedly,
returning a list of results. The first argument specifies how many times
to call timeit(). The second argument specifies the number
argument for 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 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.
print_exc(file=None)[source]
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 sys.stderr.
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:
-n N, --number=N
how many times to execute 'statement'
-r N, --repeat=N
how many times to repeat the timer (default 3)
-s S, --setup=S
statement to be executed once initially (default pass)
-t, --time
use time.time() (default on all platforms but Windows)
-c, --clock
use time.clock() (default on Windows)
-v, --verbose
print raw timing results; repeat for more digits precision
-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 -s options are treated
similarly.
If -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.
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 -r option is good
for this; the default of 3 repetitions is probably enough in most cases. On
Unix, you can use 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 -O
option (see Optimizations) for
the older versions to avoid timing SET_LINENO instructions.
It is possible to provide a setup statement that is executed only once at the beginning:
$ 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 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 hasattr() vs. try/except
to test for missing and present object attributes:
$ 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 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"))