Check spelling in a text file

spellcheck.py

#!/usr/bin/env python3

import sys, re

if len(sys.argv) not in (2,3):
    sys.stderr.write("Usage: %s dictionnary.txt [file.txt]\n\nChecks spelling of text in input file.\n" % sys.argv[0])
    sys.exit(1)

infile = open(sys.argv[2]) if len(sys.argv)>2 else sys.stdin
inwords = set(map(str.lower, re.split("[^\\w]", infile.read())))

with open(sys.argv[1]) as dictfile:
    realwords = set()
    for w in dictfile: realwords.add(w[:-1])

for word in inwords - realwords:
    print(word)