Python finding prime numbers

prime.py

import math

know_prime_number = [2,3,5,7,11]

for i in range(12,1000):
    notIs = False
    for n in know_prime_number:
        if(n <= math.sqrt(i)):
            if((i % n) == 0):
                notIs = False
                break
            else:
                notIs = True
    if(notIs):
        know_prime_number.append(i)

print("found the following prime numbers")
print(know_prime_number)