The operation method of two-dimensional arrays in Python

This article mainly introduces some Python two-dimensional array operation method, is the basic knowledge of Python learning, need friends can refer to the

You need to use a two-dimensional array in your program, and find one on the web that uses:

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#创建一个宽度为3, array of height 4 #[[0,0,0], # [0,0,0], # [0,0,0], # [0,0,0]] myList = [[0] * 3] * 4

But when the operation mylist[0][1] = 1 o'clock, it is found that the entire second column is assigned, and becomes

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[[0,1,0], [0,1,0], [0,1,0], [0,1,0]]

Why... I don't understand, back to the Python Standard Library to find the answer

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

Cases:

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>>> 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, modifying any

An element changes the entire list:

So you need to create multidimensional arrays in a different way to avoid shallow copies:

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>>> lists = [[] for I in range (3)] >>> lists[0].append (3) >>> Lists[1].append (5) >>> L Ists[2].append (7) >>> lists [[3], [5], [7]]

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

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1	myList = [ ([0] * 3) for I in range (4)]