En Sat, 30 Aug 2008 03:15:30 -0300, Steven D'Aprano
<[EMAIL PROTECTED]> escribi�:
On Fri, 29 Aug 2008 21:26:35 -0700, cnb wrote:
def averageGrade(self):
tot = 0
for review in self.reviews:
tot += review.grade
return tot / len(self.reviews)
def av_grade(self):
return sum(review.grade for review in self.reviews) / \
len(self.reviews)
Re-writing the functions so they can be tested alone:
def averageGrade(alist):
tot = 0.0
for x in alist:
tot += x
return tot/len(alist)
def av_grade(alist):
return sum(alist)/len(alist)
from timeit import Timer
# small amount of items
... alist = range(100)
Timer('averageGrade(alist)',
... 'from __main__ import alist, averageGrade').repeat(number=100000)
[3.9559240341186523, 3.4910569190979004, 3.4856188297271729]
Timer('av_grade(alist)',
... 'from __main__ import alist, av_grade').repeat(number=100000)
[2.0255107879638672, 1.0968310832977295, 1.0733180046081543]
The version with sum() is much faster. How about with lots of data?
alist = xrange(1000000)
Timer('averageGrade(alist)',
... 'from __main__ import alist, averageGrade').repeat(number=50)
[17.699107885360718, 18.182793140411377, 18.651514053344727]
Timer('av_grade(alist)',
... 'from __main__ import alist, av_grade').repeat(number=50)
[17.125216007232666, 15.72636890411377, 16.309713840484619]
sum() is still a little faster.
Mmm, in this last test you're measuring the long integer operations
performance (because the sum exceeds largely what can be represented in a
plain integer). Long integers are so slow that the difference between both
loops becomes negligible.
I've tried again using float values:
alist = [float(x) for x in xrange(1000000)]
and got consistent results for any input size (the version using sum() is
about twice as fast as the for loop)
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
