Detailed explanation of Python basic sequence (sequence)

sequence sequence

sequence (sequence) is a set of ordered elements

(Strictly speaking, it is a collection of objects, but since we have not yet introduced the concept of "object" , let’s talk about elements for now)

The sequence can contain one or more elements, or it can have no elements.

The basic data types we mentioned before can all be used as elements of the sequence. An element can also be another sequence, as well as other objects that we will introduce later.

There are two types of sequences: tuple (fixed value table; also translated as tuple) and list (table)

>>>s1 = (2, 1.3, 'love', 5.6, 9, 12, False)         # s1是一个tuple
>>>s2 = [True, 5, 'smile']                          # s2是一个list
>>>print s1,type(s1)
>>>print s2,type(s2)

The main difference between tuple and list is that once It is established that each element of the tuple cannot be changed, but each element of the list can be changed.

A sequence as an element of another sequence

>>>s3 = [1,[3,4,5]]

Empty sequence

>>>s4 = []

Reference of element

The subscript of sequence element starts from 0:

>>>print s1[0]
>>>print s2[2]
>>>print s3[1][2]

Since the elements of the list can be changed, you can assign a value to an element of the list:

>>>s2[1] = 3.0
>>>print s2

If you do this operation on a tuple, you will get an error message.

So, you can see that the sequence reference is implemented through s[], int is the subscript

Other reference methods

Scope reference: Basic style [ Lower limit: upper limit: step size]

>>>print s1[:5]             # 从开始到下标4 （下标5的元素 不包括在内）
>>>print s1[2:]             # 从下标2到最后
>>>print s1[0:5:2]          # 从下标0到下标4 (下标5不包括在内)，每隔2取一个元素 （下标为0，2，4的元素）
>>>print s1[2:0:-1]         # 从下标2到下标1

As you can see from the above, when the range is quoted, if the upper limit is specified, then the upper limit itself is not included.

Tail element reference

>>>print s1[-1]             # 序列最后一个元素
>>>print s1[-3]             # 序列倒数第三个元素

Similarly, if s1[0:-1], then the last element will not be referenced (again, not including the cap element itself)

String is a tuple

String is a special element, so you can perform tuple-related operations.

>>>str = 'abcdef'
>>>print str[2:4]

Summary

tuple elements are immutable, list elements are mutable

Sequence reference s[2], s[1:8:2]

String is a tuple

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