初学python之字符串常见操作
字符串常见操作转义，常见转义符为
R/r
In : s ='c:\windows\nt'
In :print(s)
c:\windows
t
加入转义符号
In : s =R'c:\windows\nt'
In :print(s)
c:\windows\nt
三引号的作用
In : sql ="""
...: select* from xxx where name = 'tom'
...: """
In :print(sql)
select*from xxx where name = 'tom'
join 字符串的拼接
In : a ='abcd'
In :'.'.join(a)
Out:'a.b.c.d'
In : ' #'.join(a)
Out: 'a # b# c # d'
split 字符串分割转为元组
split以某个为分界线，进行分割成若干个字符串
split默认为从左向右分割
In : s1
Out:"I'm \ta super student"
In :s1.split()
Out:["I'm", 'a', 'super', 'student']
以super关键字进行切割
In :s1.split('super')
Out:["I'm \ta ", ' student']
以引号进行切割
In :a.split("'")
Out: ['I', 'mvery sorry']
以某个单词进行切割，可以发现sorry这个单词背
In :a.split("sorry")
Out:["I'm very ", '']
默认为遇空白字符进行分割
以关键字进行切分N段
以空格进行切割成某几个段，比如从第一个空格进行分段，那么第一个空格开始的为一段，剩余的段落为一个整段
In : a = 'OnFriendship And a youth said'
In :a.split(' ',1)
Out: ['On','Friendship And a youth said']
以空格为准，分成两段，这样在分成第二个空格后面的整体又为一段
In :a.split(' ',2)
Out: ['On','Friendship', 'And a youth said']
rsplit 反向切分
一般用于取文件路径以及文件名效率比较高
取s1字符串中，以最后一个关键字为切割符，并将其最后分为1段(取反）
In : s1
Out:'/data0/python/projects'
In :s1.rsplit('/',1)
Out:['/data0/python', 'projects']
In : s1 =r'/data0/python/projects/hello.txt'
In :s1.rsplit('/',1)
Out:['/data0/python/projects', 'hello.txt']
maxsplit 平均最大切分x段，与默认切段一样，都是以当前关键字依次向后切分
In : a
Out: 'OnFriendship And a youth said'
In :a.split(' ',maxsplit=2)
Out: ['On','Friendship', 'And a youth said']
aplitlines 按行切割
In : a ="""
...: hello
...: python
...: enenhaha
...: """
In : a
Out:'\nhello\npython\nenenhaha\n'
In :a.splitlines()
Out: ['','hello', 'python', 'enenhaha']
splitlines会将回车和换行符(\n)都认为是一行
splitlines true
true 参数为保留特殊字符
In : a
Out: 'abc \nnde \r haha \n'
In :a.splitlines()
Out: ['abc', ' nde ', ' haha ']
In :a.splitlines(True)
Out: ['abc\n', ' nde \r', ' haha \n']
partition 以某个关键字为分割符 *
从左到右，将分隔字符切割成两部分
In : a
Out: 'NoPython documentation found for'
In :a.partition('ython')
Out: ('NoP', 'ython', ' documentation found for')
n :len(a.partition('P'))
Out: 3
In :a.partition('Python')
Out: ('No', 'Python', ' documentation found for')
n :len(a.partition('P'))
Out8]: 3
如果发现没有则将本身为head，并且将sep 和tail 全部被抹去
查看一个不存在的关键字：
n :a.partition('HAHAHA')
Out: ('NoPython documentation found for', '', '')
反向partition
rpartition
In :a.rpartition('Python')
Out: ('No', 'Python', ' documentation found for')
与正向不同的是，它只返回一个tail结尾
In :a.partition('hahaha')
Out: ('NoPython documentation found for', '', '')
In :a.rpartition('hahaha')
Out: ('','', 'No Python documentation found for')
这样用于筛取最后字段的话，更加方便
In :a.partition('/')
Out: ('','/', 'data0/python/projects/hello.txt')
In :a.rpartition('/')
Out:('/data0/python/projects', '/', 'hello.txt')
In :a.rpartition('/')[-1]
Out:'hello.txt'
字符大小写
upper()全部转为大写
lower()全部转为小写
In : a.upper()
Out: 'SUPERSTUDENT'
In :a.upper().lower()
Out: 'superstudent'
可以用于大小写判断时候用到
In : b ='super'
In : b in a
Out: True
In : b ina.upper()
Out: False
swapcase()互换大小写
In :a.swapcase()
Out: 'aBc'
In : a
Out: 'AbC'
字符串排版
首字母大写
In : s1
Out:"I'm \ta super student."
In :s1.title()
Out:"I'M \tA Super Student."
In :s1.capitalize()
Out:"I'm \ta super student."
字符填充
center 设置宽度
In : s1 ='abc'
In :s1.center(10)
Out:' abc '
填充字符
In : s1.center(10,'*')
Out:'***abc****'
左右填充
zfill 、 just ，当位数不足以拟定的长度时，以字符0进行补齐
左填充
In :s1.zfill(10)
Out:'0000000abc'
右填充
In : s1.ljust(10,'#')
Out:'abc#######'
字符串修改*
replace 替换，在字符中找到旧的字符将其替换为新的字符串，如果不指定count则全部替换
In : a ='www.baidu.com'
In :a.replace('w','p')
Out:'ppp.baidu.com'
指定替换的次数
In :a.replace('w','p',2)
Out:'ppw.baidu.com'
In : a ='www,www,www,www'
In :a.replace('www','p',3)
Out:'p,p,p,www'
字符都是以从左到右进行查找并替换，找到匹配的字符并且将其进行替换，如有连续的字符则当一次替换操作
In :a.replace('w','python ',3)
Out:'python python python ,www,www,www'
操作后为返回一个新的字符串，因为字符串本身是不可变的
strip去掉空格*
在字符串两端进行查找并去除指定的字符集
在输入的时候或者赋值的时候难免会出现一些空格或其他字符，如我们想过滤掉的话可以使用strip进行过滤
In : enter= input('>>>')
>>> 23
In : enter
Out: ' 23'
去掉空格
In :enter.strip()
Out: '23'
strip主要将左右两边的多余空格进行过滤
In : a ='en hahaha qie hoho '
In :a.strip()
Out: 'enhahaha qie hoho'
将关键字进行过滤，先去掉再去掉
先去掉r再去掉y，返回移除字符串头尾指定的字符生成的新字符串
In : a = 'Iam very very very sorry'
In :a.strip('r y')
Out: 'I amvery very very so'
在其取值的时候将其打散逐步去进行裁剪
In :s.strip('ry')
Out: 'I amvery very very so'
In :s.strip('r yve')
Out: 'I amvery very very so'
In :s.strip('r yso')
Out: 'I amvery very ve'
In :s.strip('r yso ')
Out: 'I amvery very ve'
In :s.strip('r yso')
Out: 'I amvery very ve'
In :s.strip('r yso er')
Out: 'I amvery very v'
lstrip()从左开始
In :s.lstrip('I ysdfsdfam')
Out: 'veryvery very sorry'
rstrip()从右开始
In :s.rstrip('I ysdfsdfam')
Out: 'I amvery very very sorr'
字符串查找*
rfind 从左到右
从-1开始查找
取当前第一个字符匹配的索引
In :a.rfind('p',-1)
Out: 11
返回值不能是负索引
index与find几乎一致，找到返回的索引
In :a.index('str')
Out: 7
count 统计子串出现次数
统计某个特殊字符出现的次数
In : a
Out: 'object to str implicitly'
In : a.count('o')
Out: 2
统计某个范围字母出现的次数
In : a.count('o',0,5)
Out: 1
从某个索引位置开始统计次数
In :a.count('o',5)
Out: 1
时间复杂度
index和count方法都是O(n) 随着列表数据增大，而效率下降
len() 为O(1)
字符串判断*
startwith 判断是否是以某个字母开头
In :s.startswith('I am')
Out: True
In : s
Out: 'I amvery very very sorry'
判断其步长开始的开头
In : s
Out: 'I amvery very very sorry'
In :s.startswith('a',2)
Out: True
判断长度范围内开头的字符
n :s.startswith('a',2,100)
Out: True
endwith() 判断结尾的字符
In :s.endswith('y')
字符串判断is \ in
isidentifier判断是否是字母和下划线开头，其他都是字母
In : a
Out: 'a5'
In :a.isidentifier()
Out: True
islower 判断全部小写
isupper 判断全部大写
isspace 判断是否包含空格
format字符串格式化
In : a ="{server} {1}:{0}".format(8888,'192.168.1.100',server="webinfo")
In :print(a)
web info192.168.1.100:8888
以元组下标方法
In : a ="{0}.{0} ".format(('mage','com'))
In :print(a)
mage.com
习题略
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