performance problem with time.strptime()

Nils Rüttershoff nils at ccsg.de
Thu Jul 2 13:30:44 CEST 2009


Hi everyone,

In my free time I translate scripts from open source projects or write
my own, to train my python skills. ATM I convert the aplogmerge.pl from
awstats. It merges multiple apache logfiles and sort the output by the
timestamps of each line.  My first version of this script hasn't a good
performance, so I started profiling. It turned out that the script spend
much time for converting the timestamps of the line into a struct_time
object. Here a code example (Python 2.6.2 on Ubuntu 7.10):

Rec = re.compile(r"^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}\s-\s\d+\s\[(\d{2}/\w+/\d{4}:\d{2}:\d{2}:\d{2})\s\+\d{4}\].*")
Line = '1.2.3.4 - 4459 [02/Jul/2009:01:50:26 +0200] "GET /foo HTTP/1.0" 200 - "-" "www.example.org" "-" "-" "-"'

def strptime():
    m = Rec.match(Line)
    if m:
        date_string = m.group(1)
	# date_string example: '02/Jul/2009:01:50:26'
        return time.strptime(date_string, "%d/%b/%Y:%H:%M:%S")

with timeit this functions takes approximate 125 sec and 29.004.081
function calls (I've configured timeit with 1.000.000 runs). A look at
the output of cProfile told me that more than the half time is spent in
locale.py:

  1000002   11.712    0.000   19.592    0.000 locale.py:316(normalize)

  1000002    3.639    0.000   23.231    0.000 locale.py:382(_parse_localename)

  1000002    5.162    0.000   30.271    0.000 locale.py:481(getlocale)



I studied the time documentation and thought that I had to set TZ in os
environ:

os.environ['TZ'] = 'Europe/Berlin'

time.set()


but that had no effect. I don't know why time.strptime() looks every
time for my locale. Maybe it's a problem with my OS locale... However.
I've introduced a work around, which works perfectly for my problem. For
time comparison I could use any sort of time representation and so I
convert to epoch:

# needed to translate month str to dig repr

Shortmonth = {'Jan' : '01',

              'Feb' : '02',

              'Mar' : '03',

              'Apr' : '04',

              'May' : '05',

              'Jun' : '06',

              'Jul' : '07',

              'Aug' : '08',

              'Sep' : '09',

              'Oct' : '10',

              'Nov' : '11',

              'Dec' : '12'}

Rec = re.compile(r"^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}\s-\s\d+\s\[(?P<day>\d{2})/(?P<month>\w+)/(?P<year>\d{4}):(?P<hour>\d{2}):(?P<min>\d{2}):(?P<sec>\d{2})\s\+\d{4}\].*")

Line = '1.2.3.4 - 4459 [02/Jul/2009:01:50:26 +0200] "GET /foo HTTP/1.0" 200 - "-" "www.example.org" "-" "-" "-"'

def epoch():

    m = Rec.match(Line)

    if m:

        result = m.groupdict()

        date_tuple = (result["year"], Shortmonth[result["month"]], result["day"], result["hour"], result["min"], result["sec"], -1, -1, -1)

        date_tuple = map(int,date_tuple)

        return time.mktime(date_tuple)


with this workaround I had a speed up to 4 times; it tooks only 31 sec
with only 5.000.009 function calls. Maybe this helps some of you, who
had the similar problems with time conversion....

...But one big question remains: Why time.strptime() checks everytime
the locale? had I missed something or could I have a problem with my OS
locale?

With python 3.1 there is no difference, unless that time.strptime() took
approx 12 sec longer... :(

regards, Nils



Here a complete test script:

#!/opt/python/2.6.2/bin/python

import time

import timeit

import cProfile

import re

# needed to tranlate month str to dig repr

Shortmonth = {'Jan' : '01',

              'Feb' : '02',

              'Mar' : '03',

              'Apr' : '04',

              'May' : '05',

              'Jun' : '06',

              'Jul' : '07',

              'Aug' : '08',

              'Sep' : '09',

              'Oct' : '10',

              'Nov' : '11',

              'Dec' : '12'}

Rec1 = re.compile(r"^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}\s-\s\d+\s\[(?P<day>\d{2})/(?P<month>\w+)/(?P<year>\d{4}):(?P<hour>\d{2}):(?P<min>\d{2}):(?P<sec>\d{2})\s\+\d{4}\].*")

Rec2 = re.compile(r"^\d{1,3}.\d{1,3}.\d{1,3}.\d{1,3}\s-\s\d+\s\[(\d{2}/\w+/\d{4}:\d{2}:\d{2}:\d{2})\s\+\d{4}\].*")

Line = '1.2.3.4 - 4459 [02/Jul/2009:01:50:26 +0200] "GET /foo HTTP/1.0" 200 - "-" "www.example.org" "-" "-" "-"'

def epoch():

    m = Rec1.match(Line)

    if m:

        result = m.groupdict()

        date_tuple = (result["year"], Shortmonth[result["month"]], result["day"], result["hour"], result["min"], result["sec"], -1, -1, -1)

        date_tuple = map(int,date_tuple)

        return time.mktime(date_tuple)

def strptime():

    m = Rec2.match(Line)

    if m:

        date_string = m.group(1)

        return time.strptime(date_string, "%d/%b/%Y:%H:%M:%S")

if __name__ == "__main__":

    t1 = timeit.Timer("epoch()","from __main__ import epoch")

    t2 = timeit.Timer("strptime()", "from __main__ import strptime")

    cProfile.run("t1.timeit();print")

    print ""

    cProfile.run("t2.timeit();print")





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