Python3笔记--字符串-优快云博客

本文详细介绍了Python中字符串的基础概念及各种实用方法，包括大小写转换、查找、替换等常见操作，并展示了如何利用内置函数进行字符串的格式调整和编码解码。

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'))#True

print(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())#True
print("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())#False
print("1".islower())#False
print("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())#True
print("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())#True
print("123a".isdigit())#False
```

isnumeric()--同上

print("123".isnumeric())#True
print("123a".isnumeric())#True

isdecimal()--字符串只包含十进制字符

print("123".isdecimal())#True
print("123a".isdecimal())#False

isspace()--如果字符只包含空格返回True,否则返回False
```
print(" ".isspace())#True
print(" \t".isspace())#True
```

转载于:https://www.cnblogs.com/byadmin/articles/foundation-1.html