一、用在数组

>>> a = [[1,3],[2,4],[3,5]]  
>>> a = array(a)  
>>> a.flatten()  
array([1, 3, 2, 4, 3, 5]) 

二、用在列表

如果直接用flatten函数会出错

>>> a = [[1,3],[2,4],[3,5]]  
>>> a.flatten()  
  
Traceback (most recent call last):  
  File "<pyshell#10>", line 1, in <module>  
    a.flatten()  
AttributeError: 'list' object has no attribute 'flatten'  

正确的用法

>>> a = [[1,3],[2,4],[3,5],["abc","def"]]  
>>> a1 = [y for x in a for y in x]  
>>> a1  
[1, 3, 2, 4, 3, 5, 'abc', 'def']  

或者（不理解）

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>>> a = [[1,3],[2,4],[3,5],["abc","def"]]  
>>> flatten = lambda x: [y for l in x for y in flatten(l)] if type(x) is list else [x]  
>>> flatten(a)  
[1, 3, 2, 4, 3, 5, 'abc', 'def']  

三、用在矩阵

>>> a = [[1,3],[2,4],[3,5]]  
>>> a = mat(a)  
>>> y = a.flatten()  
>>> y  
matrix([[1, 3, 2, 4, 3, 5]])  
>>> y = a.flatten().A  
>>> y  
array([[1, 3, 2, 4, 3, 5]])  
>>> shape(y)  
(1, 6)  
>>> shape(y[0])  
(6,)  
>>> y = a.flatten().A[0]  
>>> y  
array([1, 3, 2, 4, 3, 5])