Detect prime twins in python

prime_neighbours.py

#!/usr/bin/env python

from itertools import izip, tee 
from sys import argv, exit

def pairwise(iter):
    # See: http://docs.python.org/library/itertools.html#recipes
    a, b = tee(iter)
    next(b, None)
    return izip(a, b)

def primes(stop):
    # See: http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
    sieve = [True for i in xrange(stop + 1)] 

    for i in xrange(2, stop + 1): 
        if sieve[i]:
            for j in xrange(i + i, stop + 1, i): 
                sieve[j] = False

    return [i for i in xrange(1, stop + 1) if sieve[i]]

if len(argv) is not 3:
    print 'usage: %s start stop' % argv[0]
    exit(1)

start = max(2, int(argv[1]))
stop = int(argv[2])

for (a, b) in pairwise(primes(stop)):
    if a < start:
        continue

    if b - a == 2:
        print '%d\t%d' % (a, b)