$ python nline.py

  Output n longest lines from file    
  Syntax: nline.py [n] [filename]

$ cat string.txt

  The quick
  brown fox
  jumps over
  the lazy
  dog

$ python nline.py 2 string.txt

  brown fox
  jumps over 

import sys

# offer command line help, parse command line arguments, 
if len(sys.argv) < 3:
    print "Output n longest lines from file"
    print "Syntax:", sys.argv[0], "[n] [filename]"
    sys.exit(2)
n = int(sys.argv[1])
fname = sys.argv[2]

# attempt to open file
try:
    file = open(fname, "r")
except:
    print "Error: can not open", fname,  "for reading"
    sys.exit(1)

# first pass, detect line length, build list[line #][line length]
list = []
fline_n = 0
while file:
    fline = file.readline()
    if fline == "":
        break;
    list.append((fline_n, len(fline)))
    fline_n = fline_n + 1

# sort by line length, requires swaping values for each list pair
list = [(v, k) for k, v in list]
list.sort()

# determine how many lines to skip in final output
if len(list) <= n:
    o = 0
else:
    o = len(list) - n
# remove one list element for each line to be skipped
while o:
    del list[0]
    o = o - 1
# sort by line number, requires swaping values for each list pair
list = [(v, k) for k, v in list]
list.sort()

# second pass, read file and only output lines that are still included in list
fline_n = 0
list_n = 0
file.seek(0)
while file:
    fline = file.readline()
    if fline == "":
        break;
    if (list_n < n) and (list[list_n][0] == fline_n):
        print fline,
        list_n = list_n + 1
    fline_n = fline_n + 1
file.close()