tail.py

import sys
import linecache
import os

if os.path.isfile(sys.argv[1]):
   try:
       f = open(sys.argv[1], 'r')
   except IOError as e:
       print 'File does not exist'
   isFile = True
else:
    f = sys.stdin
    g = f.readlines()
    isFile = False

#optimize for memory
length = 0
for line in f:
    length += 1

f.close()

if isFile:
    mark = length - abs(int(sys.argv[2])) + 1
    for i in range(mark, length+1):
        sys.stdout.write(linecache.getline(sys.argv[1], i))
else:
    mark = length - abs(int(sys.argv[1]))
    for i in range(mark, length + 1):
        sys.stdout.write(g[i])