关于dff[random.choice(get_neighbors((i, j)))] += 1元胞动机的程序

def update_DFF(dff, diff):
    #for cell in diff:
    #    assert walls[cell] > -10
    #     dff[cell] += 1

    dff += diff

    for i, j in it.chain(it.product(range(1, dim_x - 1), range(1, dim_y - 1)), exit_cells):
        for _ in range(int(dff[i, j])):
            if np.random.rand() < delta: # decay
                dff[i, j] -= 1
            elif np.random.rand() < alpha: # diffusion
                dff[i, j] -= 1
                dff[random.choice(get_neighbors((i, j)))] += 1
        assert walls[i, j] > -10 or dff[i, j] == 0, (dff, i, j)
    # dff[:] = np.ones((dim_x, dim_y))
这段程序不太懂，哪位大神帮帮忙，特别是 dff[random.choice(get_neighbors((i, j)))] += 1，assert walls[i, j] > -10 or dff[i, j] == 0, (dff, i, j)这两句，谢谢！