今天学python遇到个问题，教程页面：https://www.liaoxuefeng.com/wiki/1016959663602400/1017318207388128，在做作业的时候，使用其中一个网友的代码，魔改了一下

def triangles():
    L = [1]
    while True:
        # print(L)
        yield L
        for x in range(1, len(L)):
            L[-x] = L[-x] + L[-x - 1]
        # print(L)
        L=L+[1]
        # print(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
results = []
for t in triangles():
    results.append(t)
    n = n + 1
    if n == 10:
        break

for t in results:
    print(t)

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!')

结果是测试失败，然后就做了如下修改，把过程打印了一下

for t in triangles():
    print('step',n+1,':',t)
    print('result is',results)
    results.append(t)
    print('result now is', results)
    n = n + 1
    if n == 10:
        break

打印结果发现

step 3 : [1, 2, 1]
result is [[1], [1, 2]]
result now is [[1], [1, 2], [1, 2, 1]]
step 4 : [1, 3, 3, 1]
result is [[1], [1, 2], [1, 3, 3]]
result now is [[1], [1, 2], [1, 3, 3], [1, 3, 3, 1]]
step 5 : [1, 4, 6, 4, 1]
result is [[1], [1, 2], [1, 3, 3], [1, 4, 6, 4]]
result now is [[1], [1, 2], [1, 3, 3], [1, 4, 6, 4], [1, 4, 6, 4, 1]]

仔细看会发现，第四步的时候，results[2]的值其实发生了变化，[1, 2, 1]变成了[1, 3, 3]，看上去这个列表并不是append了一个数组进去，而且append了一个数组的指针进去。

修改办法1,：把triangles方法中的

yield L
# 改为以下
yield list(L)

修改办法2：把问题中的

results.append(t)
# 改为以下
results.append(t.copy)

反正就是不能直接指向那个原方法中的L，否则会产生问题……如有高手，望解答更深层次的原因。