Python's two-dimensional array operation

You need to use a two-dimensional array in your program to find such a usage on the Web:

123456

#创建一个宽度为3，高度为4的数组#[[0,0,0], # [0,0,0],# [0,0,0],# [0,0,0]]myList =[[0] * 3] *4

But when operation mylist[0][1] = 1 o'clock, the entire second column is found to be assigned, which becomes

[[0,1,0],

[0,1,0],

[0,1,0],

[0,1,0]]

Why... The Python standard Library found the answer in the back.

List * N->n shallow copies of list concatenated, n a shallow copy of List of connections

Cases:

123456

>>> lists =[[]] *3>>> lists[[], [], []]>>> lists[0].append(3)>>> lists[[3], [3], [3]]

[[]] is a list containing an empty list element, so [[]]*3 represents 3 references to this empty list element and modifies any

An element will change the entire list:

So you need to create a multidimensional array in a different way to avoid shallow copying:

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>>> lists =[[] fori inrange(3)]>>> lists[0].append(3)>>> lists[1].append(5)>>> lists[2].append(7)>>> lists[[3], [5], [7]]

The previous two-dimensional array was created in the following way:

1	myList =[([0] * 3) for i inrange(4)]

Python's two-dimensional array operation