python list initialize

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指定长度list初始化

想要找到初始化指定长度list最快的方法。
方法一：

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length = 10
array = [[]] * length

方法二

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length = 10
array = [[] for _ in range(length)]

事实上，只有第二种方法是对的。第一种方法中，arrary中的10个[]都指向了同一个对象。。

示例

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length = 10
v1 = [[]]*length
for i in range(length):
    v1[i].append(i)
print(v1)
# [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]]

v2 = [[] for _ in range(length)]
for i in range(length):
    v2[i].append(i)

print(v2)
# [[0], [1], [2], [3], [4], [5], [6], [7], [8], [9]]