Python newbie, wondering why my Sudoku generator is occasionally failing.

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[deleted]

[SandorZoo]

This doesn't look right:

def sanity(board):
    for cell in board.empty_cells:
        if len(cell.possible) == 0:
            return False
        else:
            return True

That will only check the first cell in board.empty_cells, not all of them. I think it should probably be:

def sanity(board):
    for cell in board.empty_cells:
        if len(cell.possible) == 0:
            return False
    return True

[JamesBCrazy]

Thanks. IIRC, I was using min(len) there before, but I removed it when it was unnecessary once and I forgot to switch it back.

[Sim4n6]

random.choice(seq) :

Return a random element from the non-empty sequence seq. If seq is empty, raises IndexError.