廖雪峰 python教程 

生成器章节，有一道杨辉的题目。

杨辉三角定义如下：

          1
        1   1
      1   2   1
    1   3   3   1
  1   4   6   4   1
1   5   10  10  5   1

把每一行看做一个list，试写一个generator，不断输出下一行的list：

def triangles():
   L=[1]
   while True:
       yield L
       L.append(0)
       L = [L[i-1]+L[i] for i in range(len(L))]
    

# 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]
n = 0
for t in triangles():
    print(t)
    n = n + 1
    if n == 10:
        break