示例如下:

In [5]: [(i,j) for i in range(10) for j in range(2) ]                                                                                                                                                                                           
Out[5]:  
[(0, 0), 
 (0, 1), 
 (1, 0), 
 (1, 1), 
 (2, 0), 
 (2, 1), 
 (3, 0), 
 (3, 1), 
 (4, 0), 
 (4, 1), 
 (5, 0), 
 (5, 1), 
 (6, 0), 
 (6, 1), 
 (7, 0), 
 (7, 1), 
 (8, 0), 
 (8, 1), 
 (9, 0), 
 (9, 1)] 

for i in range(10)可以看作是一个外循环,for j in range(2)看作是一个内循环