python初學者日記：發現yield中一個類似指針的問題

今天學python遇到個問題，教程頁面：https://www.liaoxuefeng.com/wiki/1016959663602400/1017318207388128，在做作業的時候，使用其中一個網友的代碼，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)

# 期待輸出:
# [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('測試通過!')
else:
    print('測試失敗!')

結果是測試失敗，然後就做了如下修改，把過程打印了一下

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

打印結果發現

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]]

仔細看會發現，第四步的時候，results[2]的值其實發生了變化，[1, 2, 1]變成了[1, 3, 3]，看上去這個列表並不是append了一個數組進去，而且append了一個數組的指針進去。

修改辦法1,：把triangles方法中的

yield L
# 改爲以下
yield list(L)

修改辦法2：把問題中的

results.append(t)
# 改爲以下
results.append(t.copy)

反正就是不能直接指向那個原方法中的L，否則會產生問題……如有高手，望解答更深層次的原因。