How to get the 2nd line of a 19GB file - python?

Question

There are >10 million lines in a file and the total file size is 19GB, I need to get only the 2nd line.

Getting a specific line could have been done with a loop:

for i,j in enumerate(open('foobar.txt')):
  if i == 1:
    print j
    break

Or with linecache (but not for large file, since it loads everything to the RAM)

import linecache
print linecache.getline(open('foobar.txt'),2)

or with unix commands and os.popen :

import os
infile = 'foobar.txt'
print os.popen('head -2 '+infile+'|tail -1')

I am exploring more options to get only the 2nd line.

• Is there a way to read until the 2nd \\n and then stop reading? (this way it saves RAM space)
• Is there a way to read until 1GB of the file and then seek for the 2nd line?
• What other way is there to read until the 2nd line?

I assume the question is scalable, given that the x in the xth line that someone is small and the size of the file is >>>.

Answer 1

You can do the same with itertools.islice like this:

import itertools
n = 1
with open('foobar.txt') as f:
    print next(itertools.islice(f, n, n+1))