Python Primes

primes.py

#!/usr/bin/env python
import sys
import locale

locale.setlocale(locale.LC_ALL, 'en_US')

def is_prime_brute(n):
    for x in range(2, n / 2 + 1):
        if n % x == 0:
            return False
    return True

def is_prime_sieve(n, primes):
    for x in primes:
        for y in range(2, n / 2 + 1):
            z = x * y
            if z > n:
                break
            if z in primes:
                primes.remove(z)
    return n in primes

def is_prime_sieve2(n, primes):
    x = 2
    while x <= n / 2 + 1:
        if x in primes:
            for y in range(2 * x, n, x):
                if y in primes:
                    primes.remove(y)
        x += 1

def pline(msg, n=30):
    print "=" * n
    print msg
    print "=" * n    

def test(limit, alg):
    primes = range(2,limit)
    pline("using " + alg)

    if alg == 'brute':
        primes = [i for i in primes if is_prime_brute(i)]
    elif alg == 'sieve':
        is_prime_sieve(limit, primes)
    else:
        is_prime_sieve2(limit, primes)

    format = "%" + ("%d" % (len(locale.format("%d", limit, grouping=True)) + 1)) + "d"
    count = 0
    for p in primes:
        if count > 0 and count % 10 == 0:
           print ""
        sys.stdout.write(locale.format(format, p, grouping=True))
        count += 1            
    print ""
    pline("%d primes between 2 and %d" % (count, limit))

test(int(sys.argv[1]), sys.argv[2])