Python數組構造的坑

今天寫Python代碼的時候遇到了一個大坑
問題是這樣的，我需要創建一個二維數組，如下：

m = n = 3
test = [[0] * m] * n
print("test =", test)

輸出結果如下：

test = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

是不是看起來沒有一點問題？
一開始我也是這麼覺得的，以爲是我其他地方用錯了什麼函數，結果這麼一試：

m = n = 3
test = [[0] * m] * n
print("test =", test)

test[0][0] = 233
print("test =", test)

輸出結果如下：

test = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
test = [[233, 0, 0], [233, 0, 0], [233, 0, 0]]

是不是很驚訝？！
這個問題真的是折磨，去網上一搜，官方文檔中給出的說明是這樣的：

Note also that the copies are shallow; nested structures are not
copied. This often haunts new Python programmers; consider:

lists = [[]] * 3 lists [[], [], []] lists[0].append(3) lists [[3],
[3], [3]] What has happened is that [[]] is a one-element list
containing an empty list, so all three elements of [[]] * 3 are
(pointers to) this single empty list. Modifying any of the elements of
lists modifies this single list. You can create a list of different
lists this way:

lists = [[] for i in range(3)] lists[0].append(3)
lists[1].append(5) lists[2].append(7) lists [[3], [5], [7]]

也就是說matrix = [array] * 3操作中，只是創建3個指向array的引用，所以一旦array改變，matrix中3個list也會隨之改變。

建議使用列表生成式來構造list