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Need to speed up slow executing scripts

The attached scripts I have work but they take a long time to process.  They basically filters the records of a log file for a certain string and writes the records that contain that string to a new file.  I know execution is directly affectted by the size of the oringinal log file but Is there anyway to speed this up?  I have been told that some methods of reading and\ or writting to a file are faster than others.  Is the method that I am using the most efficent?  If not how do I improve it?  

The files that I am filtering are between 20 to 80 MB taking up to 50 seconds.
import os, time

from datetime import datetime, timedelta

def SpecErrLog(File, dt, err, Duration):
    source_file = open(File,"r")
        file1 = File + " " + dt.replace(":","_") + " [" +  err + "]" + str(Duration)
        #file1 = "temptry.txt"
        dest_file = open(file1, 'w')
        Mach, Dt = File.split()
        BeginDay = datetime.strptime("00:00:00.000", '%H:%M:%S.%f')
        EndDay = datetime.strptime("23:59:59.999", '%H:%M:%S.%f')
        dt = datetime.strptime(dt, '%H:%M:%S.%f')
        for line in source_file:
            LineTimeStamp = datetime.strptime(arr[4].strip(), '%H:%M:%S.%f') #timeStamp of sourcefile.
            upperLimit= dt + timedelta(minutes=Duration)
            lowerLimit= dt - timedelta(minutes=Duration)
            if lowerLimit > BeginDay and upperLimit < EndDay: #if all records accurr within the same day.
                if lowerLimit < LineTimeStamp < upperLimit:
        print "finished"
if __name__ == "__main__":

    dt = "09:52:15.710"
    err = "54300"
    SpecErrLog("H108 01-24-2011", dt, err, 30)

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1 Solution
Dave BaldwinFixer of ProblemsCommented:
Here's a page about Python compilers: http://effbot.org/zone/python-compile.htm  That might speed it up.
The link above describes how to package your Python application as an EXE file -- this is not the same as compiling it.  Python files (".py" extension), after passing through the interpreter, will be stored into a byte code representation with a ".pyc" extension.   The packages described are a way to bundle the .pyc files along with related libraries into a single executable with a .EXE extension, but this is just a convenience and does not affect execution speed.  

Standard optimization techniques that apply to any language apply here too.  It's always good to look for loop invariants - values that get calculated every time through the loop even though you get the same result every time.  You have two of them - the calculation for upperLimit and lowerLimit.  Take those two lines out of the loop and put them prior to it.  That should make some kind of difference - maybe not too dramatic, but noticeable.

Another standard optimization technique is to put your most powerful conditionals first.   First you check for lowerLimit and upperLImit being on the same day, then you check the timestamp.  But won't  the limits be on the same day most of the time?  Meaning you'll almost always fall through to the second conditional.  If the timestamp check is much less frequently satisfied, than put it first.  Then you won't fall through to the second comparison so often.   That could be important because I think those comparisons of datetime structs are probably not real efficient.

Speaking of comparing time-structs, you may be able to eliminate doing comparisons against them entirely.  It would be much quicker to compare simply numbers.  If you represented all times as the number of seconds since the January 1st, 1970 (a common convention), then you could compare all dates and times as integers rather than time_structs, which would be much quicker.  

I don't really think the file i/o is your problem.  The standard write statement is quite efficient and I've written plenty of programs that looked a lot like yours which processed files that big quite rapidly.

I hope you find these ideas helpful.  Enjoy!  

In fact, on second thought, I'm not convinced your logic is exactly correct.  You're throwing out lines where the lower limit might be less than the beginning of the day or the upper limit might be greater than the end of the day.  I think what you want to do is change the lower limit calculation so if the lower limit comes out as less than the start of the day, you make it the start of the day; and make an analagous change with the upper limit and the end of the day.  That would allow you to eliminate the beginDay and endDay comparison entirely, as well as eliminating a bug.  I don't think your way would work properly if the initial "dt" parameter is very close to the beginning or the end of the day.
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NevSoFlyAuthor Commented:

I tried your first suggestions and saved about 7 seconds but I am having a hard time trying to convert the times stamp to seconds.  I get an out of range error.  I have looked on the web but can't find another way to convert a datetime to seconds (integer).

I am trying to use your second suggestion but I think I may have to rethink my approach.  The reason is that the log files that I am pulling this data from only contain info for 1 day.  If the LineTimeStamp is less than BeginDay then I will need to open the previous days logs and search them.

So for now I think I will only work with one day and not test for BeginDay or EndDay.
NevSoFlyAuthor Commented:
if you do know of  a way to convert lowerLimit and upperLimit to seconds I'm all ears.
Working with only one day will again improve your efficiency because you will move one more slow conditional check from within to outside the loop.  That should gain you several more seconds.  

Additionally, I missed two more loop invariants!   The calculation of lowerLimit and upperLimit will give the same result every time throuh the loop too.  Those lines can be moved priorto the loop which should gain you even more time.

My suggestion about using seconds was probably my worst idea.  Using seconds will make the comparison faster, but the additional computation involved in doing the conversion might destroy the benefit or even make it worse.  I think you can safely forget about it.

Once you do all the other things we discussed, you'll have a nice tight program and it will be running about as fast as it can.   80 megabytes is not a small fiile and it will take some time under the best of circumstances.   If it gets down to the 30-second range I'd say you were doing pretty good.
NevSoFlyAuthor Commented:
thank you
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