Generates a...generator? To lazily generate nqueens solutions

nqueens_gen.py

def threatened(pos, past, n):
    for i in range(len(past)):
        if past[i] == pos or abs(pos - past[i]) == len(past) - i:
            return True
    return False

def nqueens(n, past=None):
    if past == None:
        for i in range(n):
            yield from nqueens(n, [i+1])
    else:
        if len(past) == n:
            yield past[:]
        else:
            for pos in range(1,n+1):
                if not threatened(pos, past, n):
                    yield from nqueens(n,past + [pos])

nq = nqueens(8)

print(len(list(nq)))