def primes_upto(limit: int):
    """Generate prime numbers < *limit*.""" 
    # Sieve of Eratosthene
    is_prime = [True] * limit 
    for n in range(2, limit):
        if is_prime[n]:
            yield n  # found prime number
            for c in range(n*n, limit, n):  # start with square, less values are marked already
                is_prime[c] = False # mark composites

  if __name__ == "__main__":                
    from itertools import islice
    
    print(*islice(primes_upto(100), 10)) # -> 2 3 5 7 11 13 17 19 23 29