Sort a file by first (or second, or else) column in python

The problem you're having is that you're not turning each line into a list. When you read in the file, you're just getting the whole line as a string. You're then sorting by the first character of each line, and this is always the same character in your input, 'E'.

To just sort by the first column, you need to split the first block off and just read that section. So your key should be this:

for line in sorted(lines, key=lambda line: line.split()[0]):

split will turn your line into a list, and then the first column is taken from that list.

If your input file is tab-separated, you can also use the csv module.

import csv
from operator import itemgetter
reader = csv.reader(open("t.txt"), delimiter="\t")

for line in sorted(reader, key=itemgetter(0)):
    print(line)

sorts by first column.

Change the number in

key=itemgetter(0)

for sorting by a different column.