# Python array definition method

Source: Internet
Author: User
Tags array definition
This article mainly introduces the Python array definition method, and analyzes the Python one-dimensional array and two-dimensional array definition methods and related precautions in the form of examples, for more information about how to define Python arrays, see the following example. 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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