Detailed introduction to Python array definition method

The examples in this article describe the Python array definition method. Share it with everyone for your reference, the details are as follows:

There is no data structure for arrays in Python, but lists are very similar to arrays, such as:

a=[0,1,2]

At this time: a[0]=0, a[1]=1, a[[2]=2, but it raises a question, that is, what if the array a wants to be defined as 0 to 999? This may be Implemented through a = range(0, 1000). Or omit it as a = range(1000). If you want to define a with a length of 1000, and the initial values ​​are all 0, then a = [0 for x in range(0, 1000)]

The following is a two-dimensional array Definition:

Direct definition:

a=[[1,1],[1,1]]

This defines a 2*2 two-dimensional array with an initial value of 0.

Indirect definition:

a=[[0 for x in range(10)] for y in range(10)]

This defines a 10*10 two-dimensional array with an initial value of 0.

There is also a simpler method of literal two-dimensional array:

b = [[0]*10]*10

Define a 10*10 two-dimensional array with an initial value of 0.

Compare with a=[[0 for x in range(10)] for y in range(10)]: the result of print a==b is True.

But after using the definition method of b instead of a, the program that could run normally before also went wrong. After careful analysis, the difference was found:

a[0][0]=1 , only a[0][0] is 1, and the others are all 0.

When b[0][0]=1, a[0][0], a[1][0], and a[9,0] are all 1.

From this we get that the 10 small one-dimensional data in the large array all have the same reference, that is, they point to the same address.
So b = [[0]*10]*10 does not conform to our conventional two-dimensional array.

After testing at the same time: the definition of c=[0]*10 has the same effect as c=[0 for x in range(10)], without the problem of the same reference above, it is estimated that the definition of array c At this time, the value type is multiplied, while in the previous b, the type is multiplied, because the one-dimensional array is a reference (borrowing the value type and reference type in C#, I don’t know if it is appropriate).

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