sieve.cpp

const int size = 1000000;

int main()
{
  bool li[size] = {false};

  for ( int i = 2; i < size; ++i )
  {
    if ( !li[i] )
    {
      for ( int j = i *2; j < size; j += i )
      {
        li[j] = true;
      }
    }
  }
}

sieve.py

def sieve():
    li = [True for _ in range(1000000)]

    for i in range(2, len(li)):
        if li[i] == True:
            for j in range(i * 2, len(li), i):
                li[j] = False

    return li

sieve()