字符串

 字符串

字符串不可更改

1，字符串格式化

>>> name='lily'
>>> age=20
>>> print('my name is '+ name + " , I'm " + str(age) + " years old")    #字符串拼接，不建议
my name is lily , I'm 20 years old

>>> print("my name is %s, I'm %s years old" %(name,age))    #字符串格式化 ，推荐
my name is lily, I'm 20 years old

format 格式化字符串

>>> print('my name is {} ,and age is {}'.format('lily',22))
my name is lily ,and age is 22

>>> print('my name is {0} , and age is {1}'.format('lily',22))
my name is lily , and age is 22   #位置参数

>>> print('my name is {name}, and age is {age}'.format(age=22,name='lily'))    #关键字参数
my name is lily, and age is 22

>>> dic={"name":"lily","age":18}
>>> print("name is {name},age is {age}".format(**dic))
name is lily,age is 18

:[填充字符][对齐方式 <^>][宽度]
>>> a='A'
>>> b='B'
>>> c='C'
>>> print("{0:<5}
{1:^5}
{2:>5}".format(a,b,c))
A               #左对齐    #居中     #右对齐
  B  
    C
>>> print("{:*<5}
{:*^5}
{:*>5}".format(a,b,c))
A****
**B**
****C

2，常用的字符串功能

可通过 dir(obj) 查看方法

索引      obj[0]  obj[-1]
切片      obj[1:4]  obj[::-1] 倒序
长度      len(obj)
移除空白   obj.lstrip() 去头空白    obj.strip() 两头  obj.rstrip() 去尾部空白
分割     obj.split()
大小写   obj.title()首字母大写   obj.upper() 大写  obj.lower() 小写

join() 和split()方法

join()方法是针对一个字符串而调用的，并且传入一个列表值

>>> ','.join('hello world')
'h,e,l,l,o, ,w,o,r,l,d'


>>> ' '.join(['my','name','is','lily'])
'my name is lily'

 split()方法做的事情正好相反：它针对一个字符串调用，返回一个字符串列表。

>>> 'hi python hello world'.split()
['hi', 'python', 'hello', 'world']
>>> 
>>> 'mynameislilymyageis22myaimispython'.split('my')
['', 'nameislily', 'ageis22', 'aimis

str

def capitalize(self): #首字母转换成大写
>>> 'hello world'.capitalize()
       'Hello world'

def casefold(self): # 全部转换成小写
>>> 'HELLO world'.casefold()
         'hello world'

def center(self, width, fillchar=None): # 居中
>>> 'hello world'.center(20,'-')
         '----hello world-----'

def count(self, sub, start=None, end=None): # 计数
>>> s='hello world!'
>>> s.count('l')
>>> s.count('l',1,3)

def encode(self, encoding='utf-8', errors='strict'): #编码 把str变成二进制
 
编码(encode)：string-->bytes
解码(decode)：bytes-->string 
>>> 'hello'.encode()
b'hello'
>>> 
>>> b'hello'.decode()
'hello'

def endswith(self, suffix, start=None, end=None): #以什么结尾，startswith 以什么开头

>>> 'hello'.endswith('o')
        True
>>> 'hello world'.endswith('w',1,7) #指定起始位置
        True

def expandtabs(self, tabsize=8): #字符串中的 tab ('	')转为空格
>>> s
         'hello	world'
>>> s.expandtabs()
         'hello   world'
>>> s.expandtabs(20)
         'hello               world'

def find(self, sub, start=None, end=None): #找到时返回索引，找不到时返回-1.区别于index
>>> 'hello'.find('e')   
>>> 'hello'.find('x')
        -1

def format(self, *args, **kwargs): # 格式化字符串
>>> 'my name is {1} age is {0}'.format(22,'lily')
         'my name is lily age is 22'
>>> 'my name is {name}'.format(name='lily')
         'my name is lily'

def format_map(self, mapping): # real signature unknown; restored from __doc__
        """
        S.format_map(mapping) -> str
        
        Return a formatted version of S, using substitutions from mapping.
        The substitutions are identified by braces ('{' and '}').


def index(self, sub, start=None, end=None): # 找到时返回索引，找不到时报错
>>> 'hello'.index('e')
>>> 'hello'.index('y')
         raceback (most recent call last):
         File "<stdin>", line 1, in <module>
         ValueError: substring not found

def isalnum(self): # 都是字母和数字组成
def isalpha(self):  # 都是由字母组成
def isdigit(self):    # 都是由数字组成
def isdecimal(self): #是否只包含十进制字符

def islower(self):    #是否由小写字母组成
def isnumeric(self): # 是否只由数字组成，只适用于unicode对象
def isprintable(self): #是否都是可打印字符
def isspace(self): #是否只由空格组成
def isidentifier(self): # real signature unknown; restored from __doc__

def istitle(self): # 所有单词拼写首字母为大写，且其他字母为小写。
 >>> s='Hello World'
>>> s.istitle()
        True

def isupper(self): #所有单词大写
>>> s='HI123'
>>> s.isupper()
        True
def join(self, iterable): # 用指定的字符连接序列中的元素生成一个新的字符串
>>> l=['a','b','c','d']
>>> '-'.join(l)
        'a-b-c-d'

def ljust(self, width, fillchar=None): #居左 
>>> s= 'helloworld'
>>> s.ljust(20,'*')
        'helloworld**********'



def lstrip(self, chars=None): # 去除开头的空格

def maketrans(self, *args, **kwargs): # real signature unknown
        

def partition(self, sep): #按照指定分割符将字符串分割
>>> 'hello'.partition('l')
        ('he', 'l', 'lo')

def split(self, sep=None, maxsplit=-1): # 通过指定分隔符对字符串切片
>>> 'abacadae'.split('a')
['', 'b', 'c', 'd', 'e']
>>> 'a:b:c'.split(':')
['a', 'b', 'c']

　>>> 'a:b:c'.split(':',1)
  ['a', 'b:c']

def replace(self, old, new, count=None): # old替换成new，次数（默认全部替换）
>>> 'hello'.replace('l','x')
        'hexxo'
>>> 'hello'.replace('l','x',1)
        'hexlo'

def splitlines(self, keepends=None): # real signature unknown; restored from __doc__

def strip(self, chars=None): #去掉前后空格
        """
        S.strip([chars]) -> str
        
        Return a copy of the string S with leading and trailing
        whitespace removed.
        If chars is given and not None, remove characters in chars instead.
        """
        return ""

def swapcase(self): # 大小写转换
>>> 'helloWORLD'.swapcase()
'HELLOworld'

def title(self): # 将首字母转换成大写 其他转成小写
>>> 'HELLO WORLD'.title()
         'Hello World'

def lower(self): # 全部转换成小写

def upper(self): # 全部转换成大写
>>> 'Hello World'.upper()
         'HELLO WORLD'

def translate(self, table): #根据 table 的规则（可以由 str.maketrans('a', 'b') 定制）转换字符串中的字符
>>> s
'hello world'
>>> s.translate(s.maketrans('l','x'))
'hexxo worxd'

def zfill(self, width): # 返回指定长度的字符串，原字符串右对齐，前面填充0