Python's definition and usage of strings and subscripts (examples and analysis included)

Code is composed of a string of letters; String is a word composed of letters that is understood as a word in English but is a variable in Python.

It’s like a point moving to form a line, and a line moving to form a surface. Letters are combined into words, and words are simply encapsulated to turn them into strings. In loop statements, many times we have to locate and intercept multiple strings in a variable.

This article simply introduces to classmates how to intercept letters from a string, or intercept several strings from a group of strings.

First, let’s define:

A string is a string of characters composed of numbers, letters, and underscores.

Generally recorded as

Sth=“a1a2a3a4a5a6a7.........an”(n>0)

Sth is a self-defined independent variable. For novices, we still recommend using English words as variables, which has no harm at all.

There are two types of string values ​​in Python, positive and negative values ​​(see Figure 1.1)

You can use one in It is mathematically wrong, but a very convenient pseudo-definition:

In Python, 0 is a positive integer

In this way, it is easy to understand the expression in the above figure That makes sense

About the use of subscripts and how to intercept strings

#!/usr/bin/python
# -*- coding: UTF-8 -*-                  #国之根基

This is a common convention and cannot be explained

s="Hello world"

This is the string we set ourselves

print s                        #这是对变量s整体进行输出
print s[2:7]                #这是对变量s的第二个下标（第三个字母）到第7个下标（）第八个字母进行截取输出
print s[2:]                           #这是对变量s的第二个下标（第三个字母）开始输出到结尾
print s * 2                          #*表示数学中的乘号，s*2表示对变量s输出两次
print s + "There are strings what  add in the s"     #+表示数学中的加号，可以连接两个字符串/数字

This is the interception we made in it

The following is the output Result

Hello world

llo w

llo world

Hello worldHello world

Hello worldThere are strings what add in the s

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