gistfile1.py

# N is the range in which you find all primes
N = 10000

# initialize an array of flags
is_prime = [1 for num in xrange(N)]
is_prime[0] = 0 # this is because indexing starts at zero
is_prime[1] = 0 # one is not a prime, but don't mark all of its multiples!

def set_prime(num):
    "num is a prime; set all of its multiples in is_prime to zero"
    for x in xrange(num*2, N, num):
        is_prime[x] = 0

# iterate over all integers up to N and update the is_prime array accordingly
for num in xrange(N):
    if is_prime[num] == 1:
        set_prime(num)

primes = [num for num in xrange(N) if is_prime[num]]