[Tutor] Simple Question...

R. Alan Monroe amonroe at columbus.rr.com
Sat Oct 16 22:52:16 CEST 2004

>         This will work perfectly if your file is small enough to fit in your
> computer's memory. If you want a function that does this on large 
> files, you'll have to use something in those lines:

> import random

> def randomLineFromBigFile(fileName, numLines):
>         whatLine = random.randint(1, numLines)  # choose a random line number
>         source = open(fileName, 'r')
>         i = 0
>         for line in source:
>                 i += 1
>                 if i == whatLine: return line
>         return None

>         This function uses very little (and a constant amount of) memory. The 
> downside is that you have to know the total number of lines in the file 
> (that's the numLines argument) before calling it. It's not a very hard 
> thing to do.

Wouldn't it be much quicker to do something like this?

import os.path
import random

size = os.path.getsize('test.txt')
print size

randline = random.randint(1, size)
print randline

testfile = open('test.txt', 'r')
print testfile.readline()  #read what is likely half a line
print testfile.readline()  #read the next whole line

You'd just need to add some exception handling in the event you tried
to read off the end of the file.


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