Python array definition method, python array Definition

Source: Internet
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Python array definition method, python array Definition

This article describes how to define Python arrays. We will share this with you for your reference. The details are as follows:

Python does not have an array data structure, but the list is similar to an array, for example:

a=[0,1,2]

In this case, a [0] = 0, a [1] = 1, a [[2] = 2, but a problem occurs, that is, what if array a is to be defined as 0 to 999? In this case, a = range (0, 1000) may be used. Or omitted as a = range (1000). If you want to define a with a length of 1000 and the initial value is 0, then a = [0 for x in range (0, 1000)]

The following is the definition of a two-dimensional array:

Direct definition:

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

A two-dimensional array of 2*2 with an initial value of 0 is defined here.

Indirect definition:

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

A two-dimensional array with 10x10 initially 0 is defined here.

There is also a simpler method to define two-dimensional arrays:

b = [[0]*10]*10

Defines a two-dimensional array with 10x10 initially 0.

Compare with a = [[0 for x in range (10)] for y in range (10)]: print a = B returns True.

However, after B's definition method is used to replace a, the previous programs that can run normally also failed. After careful analysis, the differences are obtained:

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

When B [0] [0] = 1, a [0] [0], a [1] [0], and only a [9, 0] is 1.

Therefore, the 10 small one-dimensional data in the large array is all referenced in the same way, that is, pointing to the same address.
Therefore, B = [[0] * 10] * 10 does not conform to the two-dimensional array in our general sense.

At the same time, the definition of c = [0] * 10 has the same effect as that of c = [0 for x in range (10, it is estimated that the definition of array c is a multiplication of the value type, while the previous B is a multiplication of the type, because the one-dimensional array is a reference (borrow the value type and reference type in C, ).

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