Go to a specific line in python?

Question

i want to go to line 34 in a .txt file and read it how would you do that? In python?

Answer 1

You could just read all the lines and index the line your after.

line = open('filename').readlines()[33]

Answer 2

There's two ways:

1. Read the file, line by line, stop when you've gotten to the line you want
2. Use f.readlines() which will read the entire file into memory, and return it as a list of lines, then extract the 34th item from that list.

Solution 1

Benefit: You only keep, in memory, the specific line you want.

code:

for i in xrange(34):
    line = f.readline();
# when you get here, line will be the 34th line, or None, if there wasn't
# enough lines in the file

Solution 2

Benefit: Much less code
Downside: Reads the entire file into memory
Problem: Will crash if less than 34 elements are present in the list, needs error handling

line = f.readlines()[33]

Answer 3

Use Python Standard Library's linecache module:

line = linecache.getline(thefilename, 33)

should do exactly what you want. You don't even need to open the file -- linecache does it all for you!

Answer 4

for linenum,line in enumerate(open("file")):
    if linenum+1==34: print line.rstrip()

Answer 5

A solution that will not read more of the file than necessary is from itertools import islice

line_number = 34

with open(filename) as f:
    # Adjust index since Python/islice indexes from 0 and the first 
    # line of a file is line 1
    line = next(islice(f, line_number - 1, line_number))

A very straightforward solution is

line_number = 34

with open(filename) as f:
    f.readlines()[line_number - 1]