python中的字符串（包含验证码的生成）

旧城等待， 2021-12-24 03:49 186阅读 0赞

## 1.python字符串的定义方式 ##

a = 'hello'
    b = "westos"
    c = 'let\'s go'
    d = "let's go"
    e = """
            用户管理系统
            1.添加用户
            2.删除用户
            3.显示用户
    """
    print(a)
    print(b)
    print(c)
    print(d)
    print(e)
    print(type(e))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 1]

## 2.python字符串的特性 ##

1.索引  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 2]  
2.切片  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 3]  
3.重复  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 4]  
4.连接  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 5]  
5.成员操作符  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 6]  
**练习：**

1.判断一个数是否是回文数（即数字是对称的）

num = input('Num:')
    if num == num[::-1]:
        print('回文数')
    else:
        print('不是')

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 7]

## 3.python字符串判断（判断字符串里面每个元素是否为某种类型） ##

1.判断字符串是不是数字（isdigit()）

print('123'.isalpha())
    print('aaa'.isalpha())

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 8]2.判断字符串是否是首字母大写，其余字母小写（title）

print ('Hello'.istitle())
    print ('HeLLo'.istitle())

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 9]  
3.判断字符串是否全是大写/小写，并将其变成全大写或全小写（upper()：变成全大写；lower()：变成全小写；isupper()：判断字符串是否是全大写；islower()：判断字符串是否是全小写）

print('hello'.upper())
    print('hello'.isupper())
    print('hElLo'.lower())
    print('hElLo'.islower())

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 10]  
4.判断字符串是否是字母或数字，(任一个)

print(‘hello123’.isalnum())

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 11]  
5.判断字符串是否是字母

print('abc123'.isalpha())
    print('abc'.isalpha())

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 12]  
6.判断字符串和后面的字符串类型是否是相对应的

print(isinstance(1,int))
    print(isinstance('a',str))
    print(isinstance(1,str))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 13]

## 4.python字符串去掉开头和结尾 ##

1.去掉字符串两边的空格

s = '    hello   '
    print(s.strip())    ##去掉两边的空格
    print(s.lstrip())   ##去掉字符串前面的空格
    print(s.rstrip())   ##去掉字符串后面的空格

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 14]  
2.去掉字符串中要求去掉的字符或符号

s = '    \nhello   '    ##去掉空格，换行
    print(s.strip())
    s1 = '    \thello   '   ##去掉空格，制表
    print(s1.strip())
    s2 = 'helloh'
    print(s2.strip('h'))    ##去掉字符串中的h
    print(s2.lstrip('he'))  ##去掉字符串左边的h或e
    print(s2.rstrip('he'))  ##去掉字符串右边的h或e
    print(s2.strip('he'))    ##去掉字符串中的he

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 15]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 16]

## 5.python字符串匹配开头和结尾 ##

1.判断字符串开头是否是http://如果是，则输出爬取该网页。更改if判断语句中匹配的字符为http:///，此时会输出错误网页。

url1 = 'file:///mnt'
    url2 = 'ftp://172.25.254.250/pub'
    url3 = 'http://172.25.254.250/index.html'
    
    if url3.startswith('http://'):
        print('爬取网页')
    else:
        print('无法爬取')

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 17]2.如果文件以.log结尾输出文件名否则输出错误。

filename = 'hello.log'
    
    if filename.endswith('.log'):
        print(filename)
    else:
        print('error')

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 18]  
3.判断变量名是否合法。

步骤：  
1.第一个字符是否为字母或者下划线  
2.如果是，继续  
3.如果不是，报错  
4.依次判断除了第一个字符以外的其他字符  
5.判度是否为字母、数字或者下划线

while True:
        s = input('变量名: ')
        if s == 'exit':
            print('退出')
            break
        if s[0].isalpha() or s[0] == '_':
            for i in s[1:]:
                if not(i.isalnum() or i == '_'):
                    print('%s变量名不合法' %s)
                    break
            else:
                print('%s变量名合法' %s)
        else:
            print('%s 变量名不合法' %s)

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 19]![在这里插入图片描述][20190626193839658.png]

## 6.python字符串的搜索和替换 ##

1.设置一个变量，返回其最小的索引和最大的索引，并替换字符串中所有的‘hello’为‘westos’

s = 'hello world hello'
    
    #find找到子串，并返回最小的索引
    print(s.find('hello'))
    print(s.find('world'))
    
    #rfind找到子串，并返回最大的索引
    print(s.rfind('hello'))
    
    #替换
    print(s.replace('hello','westos'))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 20]

## 7.python字符串的分离和连接 ##

#分离
    s = '172.25.254.250'
    # s1 = s[::-1]
    # print(s1)
    s1 = s.split('.')
    print(s1)
    s2 = s1[::-1]
    print(s1[::-1])
    
    date = '2019-06-23'
    date1 = date.split('-')
    print(date1)
    
    
    #连接
    print('-'.join(date1))
    print('.'.join(s2))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 21]

## 8.python字符串的对齐 ##

使“学生管理系统”以某种方式对齐

print('学生管理系统'.center(30))
    print('学生管理系统'.center(30,'*'))
    print('学生管理系统'.ljust(30,'*'))
    print('学生管理系统'.rjust(30,'*'))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 22]

## 9.python字符串的统计 ##

统计字符串的个数

print('hello'.count('l'))
    print('hello'.count('ll'))
    print(len('hello'))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 23]

## 10.python字符串的练习 ##

1.判断出勤记录。  
要求：  
给定一个字符串来代表一个学生的出勤纪录，这个纪录仅包含以下三个  
字符：  
‘A’ : Absent，缺勤  
‘L’ : Late，迟到  
‘P’ : Present，到场  
如果一个学生的出勤纪录中不超过一个’A’(缺勤)并且不超过两个连续的’L’(迟到),  
那么这个学生会被奖赏。  
你需要根据这个学生的出勤纪录判断他是否会被奖赏。  
示例 1:  
输入: “PPALLP”  
输出: True  
示例 2:  
输入: “PPALLL”  
输出: False

s = input()
    if s.count('A') <= 1 and s.count('LLL') == 0:
        print(True)
     else:
       print(False)

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 24]  
也可以写成两句

s = input()
    print(s.count('A') <= 1 and s.count('LLL') == 0)

![在这里插入图片描述][20190626195816168.png]  
2.字符反转  
输入：hello world python  
输出：python world hello

print(' '.join(input().split()[::-1]))

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 25]  
3.去掉指定字符  
输入：they are student  
输出：aeiou

s1 = input('s1:')
    s2 = input('s2:')
    
    for i in s1:
        if i in s2:
            s1 = s1.replace(i,'')
    
    print(s1)

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 26]

## 10.生成四位验证码 ##

import random
    import string
    
    code_str = string.ascii_letters + string.digits
    # print(code_str)
    
    def gen_code(len=4):
        return ''.join(random.sample(code_str,len))
    # gen_code()
    
    print([gen_code() for i in range(1000)])

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NDg4OTYxNg_size_16_color_FFFFFF_t_70 27]

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