[Tutor] Simple Question...

[R. Alan Monroe]

> the file. It must be capable of returning the first line, the last
> line, and anything in between.

Your fortune file was a bit hard to debug with since many lines were
blank. I'll attach the test file I ended up using.

Repeatedly opening/closing the file in question is murder, in a tight
loop. Doing an os.path.getsize() is pretty slow too. If you do both of
those on the outside of the tight loop, it really speeds up.


C:\coding\python>python randomline.py
4.13174830879 (open/close the file each time)
2.369336885 (open the file outside the loop)
0.68840117948 (open and get size outside the loop)

Times given are for 20000 iterations on a 2.4ghz laptop.

Alan
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import os.path
import random
import time


def getrandomline1(filename):
    size = os.path.getsize(filename)
    testfile = open(filename, 'r')
    firstline = testfile.readline()
    secondline = testfile.readline()

    retval=""
    while len(retval) < 1:
        randpos = random.randint(1, size)
        if randpos <= len(firstline):
            retval = firstline
        else:
            testfile.seek(randpos)
            if randpos <= len(firstline) + len(secondline):
                testfile.seek(1-len(secondline), 1)
            testfile.readline()
            retval = testfile.readline()
        
    testfile.close()
    return (randpos, retval.strip())

def getrandomline2(filename, testfile):
    size = os.path.getsize(filename)
    testfile.seek(0)
    firstline = testfile.readline()
    secondline = testfile.readline()

    retval=""
    while len(retval) < 1:
        randpos = random.randint(1, size)
        if randpos <= len(firstline):
            retval = firstline
        else:
            testfile.seek(randpos)
            if randpos <= len(firstline) + len(secondline):
                testfile.seek(1-len(secondline), 1)
            testfile.readline()
            retval = testfile.readline()
        
    return (randpos, retval.strip())

def getrandomline3(filename, testfile, size):
    testfile.seek(0)
    firstline = testfile.readline()
    secondline = testfile.readline()

    retval=""
    while len(retval) < 1:
        randpos = random.randint(1, size)
        if randpos <= len(firstline):
            retval = firstline
        else:
            testfile.seek(randpos)
            if randpos <= len(firstline) + len(secondline):
                testfile.seek(1-len(secondline), 1)
            testfile.readline()
            retval = testfile.readline()
        
    return (randpos, retval.strip())


starttime=time.clock()
for x in range(20000):
    randline=getrandomline1('test.txt')
endtime=time.clock()
print endtime-starttime


filehandle = open('test.txt', 'r')
starttime=time.clock()
for x in range(20000):
    randline=getrandomline2('test.txt', filehandle)
endtime=time.clock()
filehandle.close()
print endtime-starttime


filehandle = open('test.txt', 'r')
filesize = os.path.getsize('test.txt')
starttime=time.clock()
for x in range(20000):
    randline=getrandomline3('test.txt', filehandle, filesize)
endtime=time.clock()
filehandle.close()
print endtime-starttime