Python-字符串类型

字符串类型str
======================================基本使用======================================
1、用途：记录描述性值的状态，比如名字、性别等

2、定义方式
msg='hello world' #msg=str('hello world')

类型转换: 可以把任意类型专场字符串类型
res1=str(10)
res2=str(10.3)
res3=str([1,2,3])
res4=str({'x':1}) #res4="{'x':1}"

print(type(res1))
print(type(res2))
print(type(res3))
print(type(res4))


3、常用操作+内置的方法
优先掌握的操作：（*****）
1、按索引取值(正向取+反向取) ：只能取
msg='hello world'

print(type(msg[0]))
print(msg[-1])

msg[0]='H'


2、切片(顾头不顾尾，步长)
msg='hello world'
print(msg[0]+msg[1]+msg[2])
print(msg[0:5])
print(msg[0:5:2]) #0 2 4
print(msg[0:]) #
print(msg[:]) #


print(msg[-1:-5:-1]) #-1 -2 -3 -4
print(msg[::-1]) #-1 -2 -3 -4

3、长度len：统计的是字符的个数
msg='h你d'
print(len(msg))

4、成员运算in和not in：判断一个子字符串是否存在与一个大字符串中
msg='hello world'
print('ho' in msg)
print('ho' not in msg)


5、移除空白strip:移除字符串左右两边的某些字符
msg='      hello      '

print(msg.strip(' '))
print(msg.strip())
print(msg)

name=input('name>>>: ').strip() #name='egon'
pwd=input('password>>>: ').strip()

if name == 'egon' and pwd == '123':
    print('login successfull')
else:
    print('username or password error')

msg='***h**ello**********'
print(msg.strip('*'))

msg='*-=+h/ello*(_+__'
print(msg.strip('*-=+/(_'))


6、切分split: 把有规律的字符串切成列表从而方便取值
info='egon:18:180:150'
res=info.split(':',1)
print(res)
print(res[1])


info='egon:18:180:150'
res=info.split(':')
print(res)


s1=res[0]+':'+res[1]+':'+res[2]+':'+res[3]
s1=''
for item in res:
    s1+=item
print(s1)


s1=':'.join(res)
print(s1)

':'.join([1,2,3,4,5])

7、循环
for i in 'hello':
    print(i)



需要掌握的操作（****）
1、strip,lstrip,rstrip
msg='*****hello****'
print(msg.strip('*'))
print(msg.lstrip('*'))
print(msg.rstrip('*'))

2、lower,upper
msg='AaBbCc123123123'
print(msg.lower())
print(msg.upper())

3、startswith,endswith
msg='alex is dsb'
print(msg.startswith('alex'))
print(msg.endswith('sb'))

4、format的三种玩法
msg='my name is %s my age is %s' %('egon',18)
print(msg)

msg='my name is {name} my age is {age}'.format(age=18,name='egon')
print(msg)

了解
msg='my name is {} my age is {}'.format(18,'egon')
msg='my name is {0}{0} my age is {1}{1}{1}'.format(18,'egon')
print(msg)


5、split,rsplit
cmd='get|a.txt|33333'
print(cmd.split('|',1))
print(cmd.rsplit('|',1))


6、replace
msg='kevin is sb kevin kevin'
print(msg.replace('kevin','sb',2))

7、isdigit #当字符串内为纯数字时结果为True
res='11111'
print(res.isdigit())
int(res)

age_of_bk=18
inp_age=input('your age: ').strip()
if inp_age.isdigit():
    inp_age=int(inp_age) #int('asdfasdfadfasdf')
    if inp_age > 18:
        print('too big')
    elif inp_age < 18:
        print('to small')
    else:
        print('you got it')
else:
    print('必须输入纯数字')



了解（**）
1、find,rfind,index,rindex,count
print('xxxkevin is sb kevin'.find('kevin'))
print('xxxkevin is sb kevin'.index('kevin'))
print('xxxkevin is sb kevin'.rfind('kevin'))
print('xxxkevin is sb kevin'.rindex('kevin'))


res='xxxkevin is sb kevin'.find('kevasdfsadfin')
print(res)

res='xxxkevin is sb kevin'.index('kevasdfsadfin')



print('kevin is kevin is kevin is sb'.count('kevin'))

2、center,ljust,rjust,zfill
print('egon'.center(50,'*'))
print('egon'.ljust(50,'*'))
print('egon'.rjust(50,'*'))
print('egon'.zfill(50))

3、captalize,swapcase,title
print('my name is kevin'.capitalize())
print('AaBbCc'.swapcase())
print('my name is kevin'.title())

4、is其他
name='egon123'
print(name.isalnum()) #字符串由字母或数字组成
print(name.isalpha()) #字符串只由字母组成

print(name.islower())
print(name.isupper())
name='    '
print(name.isspace())
msg='I Am Egon'
print(msg.istitle())




======================================该类型总结====================================
存一个值

有序

不可变（1、可变：值变，id不变。可变==不可hash 2、不可变：值变，id就变。不可变==可hash）
x='aaa'
print(id(x))
x='bbb'
print(id(x))