Python -- 生成器

杨辉三角

把每一行看作一个list,试写一个 generator,不断输出下一行的list。 
期待输出： 

[1]
[1, 1]
[1, 2, 1]
[1, 3, 3, 1]
[1, 4, 6, 4. 1]
[1, 5, 10, 10, 5, 1]
[1, 6, 15, 20, 15, 6, 1]
[1, 7, 21, 35, 35, 21, 7, 1]
[1, 8, 28, 56, 70, 56, 28, 8, 1]
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]

代码：

 1 # -*- coding: utf-8 -*-
 2 def triangles():
 3     L = [1]
 4     while True:
 5         yield L
 6         L.append(0)
 7         L = [L[i-1]+L[i] for i in range(len(L))]
 8 n = 0
 9 results = []
10 for t in triangles():
11     print(t)
12     results.append(t)
13     n = n + 1
14     if n == 10:
15         break

理解第7行

Step1： L = [L[i-1]+L[i] for i in [1,0])]

Step2:  L = [(L[-1]+L[0]), (L[0]+L[1]) ]

Step3:  L = [(0+1),(1+0) ] = [1, 1]