1、要記住，python預設是按行取元素

-1是模糊控制的意思 比如人reshape（-1,2）固定2列 多少行不知道

結果：

2、出錯情況

>>> a = np.array([[1,2,3], [4,5,6]])
>>> np.reshape(a, (3,-1)) # the unspecified value is inferred to be 2
array([[1, 2],
       [3, 4],
       [5, 6]])

>>> np.reshape(a, (-1,-1))
 

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 224, in reshape
    return reshape(newshape, order=order)
ValueError: can only specify one unknown dimension

np.reshape(a, (4,-1
 
))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 224, in reshape    return reshape(newshape, order=order)
ValueError: total size of new array must be