execution time
David Hláčik
#! /usr/bin/python
import random
import bucket2
data = [ random.randint(1,25) for i in range(5)]
print "random data : %s" % data
print "result: %s" %bucket2.sort(data)
How to write a test script which will outputs execution time for
bucket2.sort(data) ?
Thanks in advance!
Bruno Desthuilliers
Andreas Kostyrka
> Hi guys,
>
> #! /usr/bin/python
>
> import random
> import bucket2
>
> data = [ random.randint(1,25) for i in range(5)]
> print "random data : %s" % data
> print "result: %s" %bucket2.sort(data)
>
> How to write a test script which will outputs execution time for
> bucket2.sort(data) ?
Well:
import time
starttime = time.time()
....
endtime = time.time()
print "Whatever .... does, it took %5.3fs to do." % (endtime - starttime)
Alternativly take a look at the timeit standard module.
Andreas
>
> Thanks in advance!
> --
> http://mail.python.org/mailman/listinfo/python-list
Steven D'Aprano
> On Sun, Dec 14, 2008 at 05:03:38PM +0100, David Hláčik wrote:
>> Hi guys,
>>
>> #! /usr/bin/python
>>
>> import random
>> import bucket2
>>
>> data = [ random.randint(1,25) for i in range(5)] print "random data :
>> %s" % data
>> print "result: %s" %bucket2.sort(data)
>>
>> How to write a test script which will outputs execution time for
>> bucket2.sort(data) ?
>
> Well:
>
> import time
>
> starttime = time.time()
>
> ....
>
> endtime = time.time()
> print "Whatever .... does, it took %5.3fs to do." % (endtime -
> starttime)
Is subject to lots of timing errors for small code snippets. Sorting five
numbers is (probably) going to be very quick, so the random timing errors
will probably be larger than the time it actually takes to sort!
Just for reference, here's the size of errors from timing naively on my
machine:
def timer(alist):
from time import time
t = time()
alist.sort()
return time() - t
def make_list():
from random import random
return [random() for i in range(5)]
data = [timer(make_list()) for i in range(100)]
mean = sum(data)/len(data)
average_error = sum(abs(x-mean) for x in data)/len(data)
print "The average timing is %f seconds." % mean
print "The average error is %f seconds." % average_error
print "Percentage error: %f%%" % (average_error/mean*100)
And here is the output:
The average timing is 0.000050 seconds.
The average error is 0.000089 seconds.
Percentage error: 177.953157%
What this tells us is that the likely error in any one timing of a small
code snippet using time.time() directly is so large that it is useless
for anything other than the most crude measurements. Using time() on its
own is a good example of "measure with micrometer, mark with chalk, cut
with axe". This is precisely the problem the timeit module is written to
solve.
> Alternativly take a look at the timeit standard module.
I'd reverse that recommendation: start with the timeit module first, and
if and only if it is unsuitable, consider writing your own solution.
--
Steven