goldbach.py

def first_clear(arr, idx):
    for i in range(idx, len(arr)):
        if arr[i] == 0:
            return i
    return -1

def find_all_primes_upto(n):
    sieve = [0] * (n+1)

    i = 2
    while i>-1:
        idx = i
        while i+idx < n+1:
            i += idx
            sieve[i] = 1
        i = first_clear(sieve, idx+1)
    return [i for i in range(2, len(sieve)) if sieve[i]==0]

def find_two_primes_sum_to(n):
    primes = find_all_primes_upto(n)
    d = set()
    for prime in primes:
        other = n - prime
        if other in d:
           return other, prime
        else:
            d.add(prime)
    return None


a = [100, 489932, 1000000, 6788, 234, 1290]

for e in a:
    print (find_two_primes_sum_to(e))