random.sample(sequence, k)，从指定序列中随机获取指定长度的片断。sample函数不会修改原有序列

numpy.nonzero() Return the indices of the elements that are non-zero.

>>> a = np.array([[1,2,3],[4,5,6],[7,8,9]])>>> a > 3array([[False, False, False],       [ True,  True,  True],       [ True,  True,  True]], dtype=bool)>>> np.nonzero(a > 3)(array([1, 1, 1, 2, 2, 2]), array([0, 1, 2, 0, 1, 2]))