什么是字符串？
是以单引号或双引号括起来的任意文本如：
string1 = 'abc' string2 = "cde"
字符串是不可变的，即以下尝试修改字符串的做法是错误的：
string = 'admin'string[0] = 'b' #会报出异常--TypeError: 'str' object does not support item assignment
字符串的方法
- eval()--它可以将字符串str当成有效的表达式来求值并返回计算结果
print(eval('-135'))#-135 print(eval("12+3"))#15 print(eval("12-3"))#9 print(eval("{'key':'value'}"))#此处返回一个字典{'key':'value'} - len()--返回字符串的长度
print(len("sunck is a good man!"))#20 - lower()--转换字符串中大写字母为小写字母
string="SUNCK is A Good Man"print('string=%s'% string.lower()) #string=sunck is a good man - upper()--将字符串所有小写字母转换成大写字母
string="SuNck Is a gOOd man"print(string.upper()) #SUNCK IS A GOOD MAN
- swapcase()--转换字符串中字母的大小写
string="SuNck Is a gOOd man"print(string.swapcase()) #sUnCK iS A GooD MAN
- capitalize()--最首字母大写，其他小写
string="SuNck Is a gOOd man"print(string.capitalize()) #Sunck is a good man
- title()--每个单词首字母大写
string="SuNck Is a gOOd man"print(string.title()) #Sunck Is A Good Man
- center(width,fillchar)--字符串居中两边填充fillchar(默认空格)宽为width
string="SuNck Is a gOOd man"print(string.center(40,"*")) #**********SuNck Is a gOOd man***********
- ljust(width[,fillchar])--返回一个指定宽度的左对齐字符串，fillchar为填充字符,填在右边
string="SuNck Is a gOOd man"print(string.ljust(40,"%")) #SuNck Is a gOOd man%%%%%%%%%%%%%%%%%%%%%
- rjust(width[,fillchar])--返回一个指定宽度的有=右对齐字符串，fillchar为填充字符,填在左边
string='you are nice man'print(string.rjust(40,'*')) #************************you are nice man
- zfill(width)--返回一个长度为width的字符串，原字符串右对齐，前面补0
string='she was beautiful'print(string.zfill(40))#00000000000000000000000she was beautiful
- count(str[,start][,end])--返回字符串中str出现次数，可指定范围
string='he is very very handsome'print(string.count('very'))#2 - find(str[,start][,end])--检测str字符串是否在字符串中，返回第一次出现的开始下标，没有返回-1
string='he is very very handsome'print(string.find('very')) #6 - rfind(str[,start][,end])--从右检测str字符串是否在字符串中，返回第一次出现的开始下标，没有返回-1
string='he is very very handsome'print(string.rfind('very'))#11 - index(str,start=0,end=len(str))--跟find（）一样，只不过如果str不存在会返回异常
string='kaige is a very very nice man'print(string.index('very'))#11 - rindex(str,start=0,end=len(str))--跟index（）一样，只不过从右开始检索
string='kaige is a very very nice man'print(string.rindex('very'))#16 - lstrip()--截掉字符串左侧指定的字符，默认为空格
string='******kaige is a very nice man'print(string.lstrip('*'))#kaige is a very nice man - rstrip()--截掉字符串右侧指定的字符，默认为空格
string='******kaige is a very nice man*****'print(string.rstrip('*'))#******kaige is a very nice man - strip(str)--截去字符串两边str
string='********kaige is a very nice man******'print(string.strip('*')#kaige is a very nice man - split(str='',num)--以str为分隔符截取字符串，指定截num个。
string="sunck**is*****a***good*man"list_=string.split("*")print(list_) #['sunck', '', 'is', '', '', '', '', 'a', '', '', 'good', 'man'] - splitlines([keepends])--按照（‘\r’，‘\r\n’，‘\n’）分隔,keepends=True ，会保留换行符。默认为False
string='''sunck is a good man!sunck is a handsomoe man!sunck is a nice man!'''print(string.splitlines())#['sunck is a good man!', 'sunck is a handsomoe man!', 'sunck is a nice man!']
- join(seq)--以指定的字符串分隔符，将seq中的所有元素组合
list_=['sunck','is','a','good','man']str2="*".join(list_)print(str2)#sunck*is*a*good*man
- max()、min()--它们作用于字符串是以ascii码表顺序比较大小
max('a','A')#'a' - replace(oldstr,newstr,count)--用newstr替换oldstr,默认是全部替换。如果指定了count，那么就替换前count个
string="sunck is a good good good man"string=string.replace("good","nice",1)print(string)#sunck is a nice good good man - startswith(str,start=0,end=len(str))--判断在给定的范围内是否以给定的字符串开头，如果没有给定范围， 则默认整个字符串
string="sunck is a nice man"print(string.startswith('sunck'))#Trueprint(string.startswith("sunck",5,16)#False - endswith(str,start=0,end=len(str))--判断在给定的范围内是否以给定的字符串结尾，如果没有给定范围， 则默认整个字符串
string="sunck is a great man"print(string.endswith("man"))#True - encode(encoding="utf-8",errors="strict")--编码
string="sunck is a good man"data=string.encode("utf-8")print(data)#b'sunck is a good man' - decode()--解码 注意：要与编码的格式一致
string="sunck is a good man"data=string.encode("utf-8")string=data.decode("utf-8")print(string)#sunck is a good man - isalpha()--如果字符串中至少有一个字符，且所有字符都是字母返回True,否则为False
string="sunckisagoodman"print(string.isalpha())#True
- isalnum()--如果字符串中至少有一个字符，且所有字符都是字母或数字返回True,否则返回False
string="1a2b3"print(string.isalnum())#True
- isupper()--如果字符串字至少有一个英文字符且所有英文字符都是大写返回True，否则为False
print("AB#C".isupper())#Trueprint("1".isupper())#False - islower()--如果字符串字至少有一个英文字符且所有英文字符都是小写返回True，否则为False
print("abcA".islower())#Falseprint("1".islower())#Falseprint("abc".islower())#True - istitle()--如果字符串是标题化的返回True,否则返回False
print("Sunck Is".istitle())#Trueprint("Sunck is".istitle())#False - isdigit()--如果字符串中只包含数字字符返回True,否则返回False
print("123".isdigit())#Trueprint("123a".isdigit())#False - isnumeric()--同上
print("123".isnumeric())#Trueprint("123a".isnumeric())#True - isdecimal()--字符串只包含十进制字符
print("123".isdecimal())#Trueprint("123a".isdecimal())#False - isspace()--如果字符只包含空格返回True,否则返回False
print(" ".isspace())#Trueprint(" \t".isspace())#True