Performs an outer join type deal on two files. Finds lines in A not found in B and lines in B not found in A

outerdiff.py

import sys

def getContents(inFile):
   return sorted(list(set(inFile.read().split("\n"))), key=lambda k: k.lower())

lFileName = raw_input("Enter the first file name: ") if len(sys.argv) < 2 else sys.argv[1]
with open(lFileName, "r") as left:
   leftLines = getContents(left)

rFileName = raw_input("Enter the second file name: ") if len(sys.argv) < 3 else sys.argv[2]
with open(rFileName, "r") as right:
   rightLines = getContents(right)

lineList = []

lineList.extend([lnk for lnk in leftLines if lnk not in rightLines])
lineList.extend([lnk for lnk in rightLines if lnk not in leftLines])


print "\n".join(lineList)