Prime numbers searching using Python (with optimizations)

prime-opt.py

def prime(num):
    primes = []
    def is_prime(n):
        limit = int(n**0.5) + 1
        for i in primes:
            if i > limit:
                return True
            elif n % i == 0:
                return False
        return True
    for i in range(2, num):
        if is_prime(i):
            primes.append(i)
    return primes

print prime(1000000)