a = np.arange(3) # a.shape = (3,) b = a.reshape((3,1)) # b.shape = (3,1) b2 = a.reshape((-1,1)) # b2.shape = (3,1) c = b.reshape((3,)) # c.shape = (3,) c2 = b.reshape((-1,)) # c2.shape = (3,)