erastothenes.py

import itertools
import time


class Sieve:
    primes = [2, 3, 5, 7]
    def __init__(self, end=-1):
        self.end = end

    def __iter__(self):
        for n in itertools.count(start=11):
            if str(n)[-1:] in ['1', '3', '7', '9']: # Yes this is actually faster from 3 primes onwards
                if not any(n % p == 0 for p in self.primes):
                    self.primes.append(n)
                    yield n
            if n == self.end:
                break


if __name__ == "__main__":
    sieve = Sieve(end=100000)
    start = time.time()
    try:
        for prime in sieve:
            pass
    except KeyboardInterrupt:
        pass
    
    print('\nFound {} Primes in {} seconds.'.format(len(sieve.primes), time.time() - start))
    print('Biggest: {}'.format(sieve.primes.pop(-1)))