杨辉三角形使用python生成器实现

近日，学习python生成器的过程中遇到一些小问题。 解释器Python3.7.1
本人参照廖雪峰的博客学习，在学到生成器时，课后练习是生成杨辉三角形，网上找到一个思路不错的代码，代码如下：

# -*- coding: utf-8 -*-


def triangles():

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


# 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
results = []
for t in triangles():
    print(t)
    results.append(t)
    n = n + 1
    if n == 10:
        break
print(results)
if results == [
    [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]
]:
    print('测试通过!')
else:
    print('测试失败!')

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]
[[1, 0], [1, 1, 0], [1, 2, 1, 0], [1, 3, 3, 1, 0], [1, 4, 6, 4, 1, 0], [1, 5, 10, 10, 5, 1, 0], [1, 6, 15, 20, 15, 6, 1, 0], [1, 7, 21, 35, 35, 21, 7, 1, 0], [1, 8, 28, 56, 70, 56, 28, 8, 1, 0], [1, 9, 36, 84, 126, 126, 84, 36, 9, 1]]
测试失败!

结果总是测试失败，经过一番查找后，原因在于yield a后紧跟了一句a.append(0)。
直接将a的指向的对象改变了，而 id(a) 没变，results也跟着变了。（即 id(a)=id(results)）

修改后代码完美运行：

# -*- coding: utf-8 -*-

def triangles():

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

成功输出：

[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]
[[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]]
测试通过!