python全栈开发从入门到放弃之字符串的应用

1、strip

strip 脱去（...的）衣服

去掉左右两边的空白msg=' hellprint(msg)

  1 print(msg.strip()) #去掉左右两边的空白
  2
  3 hello
  4 hello
  5
  6 msg='********hello************'
  7 print(msg)
  8 print(msg.strip('*')) #指定的去掉左右两边的*
  9 ********hello************
 10
 11 hello
 12 (1)lstrip 指定去掉左边的*
 13 # print(msg.lstrip('*'))
 14 msg='********hello************'
 15 print(msg)
 16 print(msg.lstrip('*')) #指定去掉左边的*
 17 ********hello************
 18 hello************
 19
 20 (2)rstrip 指定去掉右边的连续的*
 21 # print(msg.rstrip('*'))
 22 msg='********hello************'
 23 print(msg)
 24 print(msg.rstrip('*')) #指定去掉右边的连续的*
 25 ********hello************
 26 ********hello

#strip的用处
# while True:
# name=input('user: ').strip()
# password=input('password: ').strip()
#
# if name == 'egon' and password == '123':
# print('login successfull')

2、split 切分

 1 info='root:x:0:0::/root:/bin/bash'
 2 print(info[0]+info[1]+info[2]+info[3])
 3 root

 info='root:x:0:0::/root:/bin/bash'
 print(info[0]+info[1]+info[2]+info[3])

 info='root:x:0:0::/root:/bin/bash'
 print(info[0]+info[1]+info[2]+info[3])
 info='root:x:0:0::/root:/bin/bash'
 print(info[0]+info[1]+info[2]+info[3])

 user_l=info.split(':') #用内置方法以‘：’能把字符串类型以列表的形式呈现出来，来取值
 print(user_l[0])

 # msg='hello world egon say hahah'
 # print(msg.split()) #默认以空格作为分隔符
 msg='hello world egon say hahah'
 print(msg.split()) #默认以空格为分隔符
 ['hello', 'world', 'egon', 'say', 'hahah']

 cmd='download|xhp.mov|3000'
 # cmd_l=cmd.split('|')
 # print(cmd_l[1])
 # print(cmd_l[0])

 # print(cmd.split('|',1))

用处
# while True:
# cmd=input('>>:　').strip()
# if len(cmd) == 0:continue
# cmd_l=cmd.split()
# print('命令是:%s 命令的参数是:%s' %(cmd_l[0],cmd_l[1]))

3、len 长度

 1 # print(len('hell 123'))
 2 print(len('hell 123')) #查看字符串的长度
 8   #字符串长度为8

4、索引

根据索引来取出子字符串

 msg='hello world
 print(msg[1:3]) #1 2
 print(msg[1:4]) #1 2 3
 msg='hello world'
 print(msg[1:3]) #切出字符串子集但顾头不顾尾
 el

5、混合应用

 oldboy_age=84
 while True:
 age=input('>>: ').strip()
 if len(age) == 0:continue
 if age.isdigit():
 age=int(age)
 else:
 print('must be int')

6、endswith

 #startswith,endswith
 # name='alex_SB'
 # print(name.endswith('SB')) #查找字符串结尾里是否有输入的参数，有着返回True,没有返回False
 # print(name.startswith('alex')) #查找开头是否有输入的参数，有着返回True，没有返回False

7、replace

 #replace
 # name='alex say :i have one tesla,my name is alex'
 # print(name.replace('alex','SB',1))
 name = 'alex say :i have one tesla,my name is alex'
 print(name.replace('alex','SB',1)) #在开头和结尾添加指定字符
 SB say :i have one tesla,my name is alex

8、占位符

 # %s对应所有字符 一一对应后面的元素
 print('my name is %s my age is %s my sex is %s' %('egon',18,'male'))
 #把{}当作一个占位符，.format调用对应每一个后面输入的字符
 print('my name is {} my age is {} my sex is {}'.format('egon',18,'male'))
 my name is egon my age is 18 my sex is male
 #根据{}里的索引来对应值，当{}没有值时默认为一一对应。
 print('my name is {0} my age is {1} my sex is {0}:{2}'.format('egon',18,'male'))
 my name is egon my age is 18 my sex is egon:male
 #根据{}里的输入的key来准确调用key对应的元素
 print('my name is {name} my age is {age} my sex is {sex}'.format(
 sex='male',
 age=18,
 name='egon'))
 my name is egon my age is 18 my sex is male

9、find、index、count查找

 #可以指定范围查找但顾头不顾尾，找到则返回该值的索引号，没有则返回-1不报错，
 # find 查找
 name='goee say hello'
 print(name.find('e',1,3))
 #index 查找
 可以指定范围查找但顾头不顾尾，找到则返回该字符串的索引号，没有则报错
 name='goee say hello'
 print(name.index('s'))

 #count
 指定参数，查找字符串里的元素，有则返回这个查找的值里有多少数，有1个就返回1，2个就返回2 等等，没有则返回0
 name='aaaaaaaa aaaaa aaa'
 print(name.count('a'))
 16

10、join

 #join
 # info='root:x:0:0::/root:/bin/bash'
 # print(info.split(':'))

 # l=['root', 'x', '0', '0', '', '/root', '/bin/bash']
 # print(':'.join(l))

 #join 两个物体连接处
 指定分隔符默认，用:连接起来
 l=['root', 'x', '', '', '', '/root', '/bin/bash']
 print(':'.join(l))
 root:x:0:0::/root:/bin/bash

11、lower,upper大小写转换

 #lower,upper
 # name='eGon'
 # print(name.lower())
 # print(name.upper())
 将大写字母全转为小写字母
 name = 'Egon'
 print(name.lower())
 egon

 将小写字母全转为大写
 name = 'Egon'
 print(name.upper())

了解部分

1、expandtabs 指定参数多少个空格符

 name='egon\thello'
 print(name)
 print(name.expandtabs(3))
 egon    hello
 egon hello

2、center,ljust,rjust,zfill

 以原有的变量的字符为中心两边添加指定数量的符号
 name='egon'
 print(name.center(30,'_'))
 _____________egon_____________

 ljust
 原有元素左对齐后面添加指定数量的符号
 name='egon'
 print(name.ljust(30,'*'))
 egon**************************
 rjust
 原有元素右对齐，往左边添加指定数量的符号
 name='egon'
 print(name.rjust(30,'*'))

3、captalize,swapcase,title

 captalize
 首字母大写，其余部分小写
 name='eGOn'
 print(name.capitalize())
 Egon

 title
 每个单词的首字母大写
 msg='egon say hi'
 print(msg.title())

 swapcase
 小写互相对调大写变小写，小写变大写
 name='eGOn'
 print(name.swapcase())
 EgoN

#在python3中

4、元素判断

  1 isdigit 是否为数字
  2 判断字符串里是否为数字，是则返回True，不是则返回False
  3
  4 num0=''
  5 num1=b'' #bytes
  6 num2=u'' #unicode,python3中无需加u就是unicode
  7 num3='四' #中文数字
  8 num4='Ⅳ' #罗马数字
  9
 10 print(num0.isdigit())
 11 print(num1.isdigit())
 12 print(num2.isdigit())
 13 print(num3.isdigit())
 14 print(num4.isdigit())
 #isdecimal:str,unicode
 # num0='4'
 # num1=b'4' #bytes
 # num2=u'4' #unicode,python3中无需加u就是unicode
 # num3='四' #中文数字
 # num4='Ⅳ' #罗马数字
 # print(num0.isdecimal())
 # # print(num1.)
 # print(num2.isdecimal())
 # print(num3.isdecimal())
 # print(num4.isdecimal())

 isdecimal
 判断一个数是否为十进制数，是则返回True,不是则返回False
 num0=''
 num1=b''
 num2=u''
 num3='四'
 num4='Ⅳ'
 print(num0.isdecimal())
 print(type(num1))
 print(num2.isdecimal())
 print(num3.isdecimal())
 print(num4.isdecimal())
 True
 <class 'bytes'>
 True
 False
 False

 #isnumeric:str,unicode,中文，罗马
 # num0='4'
 # num1=b'4' #bytes
 # num2=u'4' #unicode,python3中无需加u就是unicode
 # num3='四' #中文数字
 # num4='Ⅳ' #罗马数字
 #
 # print(num0.isnumeric())
 # # print(num1)
 # print(num2.isnumeric())
 # print(num3.isnumeric())
 # print(num4.isnumeric())

 isnumeric 同质异构的
 只针对与unicode字符的判断是否为数字，是则为真不是则为假
 num0=''
 num1=b''
 num2=u''
 num3='四'
 num4='Ⅳ'
 print(num0.isnumeric())
 print(type(num1))
 print(num2.isnumeric())
 print(num3.isnumeric())
 print(num4.isnumeric())
 True
 <class 'bytes'>
 True
 True
 True

5、is其他 isalnum、isalpha

 # name='egon123'
 # print(name.isalnum()) #字符串由字母和数字组成
 # name='asdfasdfa sdf'
 # print(name.isalpha()) #字符串只由字母组成
 #
 isalnum 字符测试
 测试变量里的元素是否为字母和数字组成
 name = 'egon123'
 print(name.isalnum())
 True