1、作用
2、定义
msg='hello' # msg=str('msg')
print(type(msg))3、类型转换
str可以把任意其他类型都转成字符串
res=str({'a':1})
print(res,type(res))4、使用：内置方法
4.1 优先掌握
4.1.1、按索引取值(正向取+反向取) ：只能取
msg='hello world'正向取
print(msg[0])
print(msg[5])反向取
print(msg[-1])只能取
msg[0]='H'4.1.2、切片:索引的拓展应用，从一个大字符串中拷贝出一个子字符串
msg='hello world'顾头不顾尾
res=msg[0:5] #x
print(res)
print(msg)步长
res=msg[0:5:2] # 0 2 4
print(res) # hlo反向步长(了解)
res=msg[5:0:-1]
print(res) #" olle"
msg='hello world'
res=msg[:] # res=msg[0:11]
print(res)
res=msg[::-1] # 把字符串倒过来
print(res)4.1.3、长度len
msg='hello world'
print(len(msg))4.1.4、成员运算in和not in
判断一个子字符串是否存在于一个大字符串中
print("alex" in "alex is sb")
print("alex" not in "alex is sb")
print(not "alex" in "alex is sb") # 不推荐使用4.1.5、移除字符串左右两侧的符号strip
默认去掉的空格
msg=' egon '
res=msg.strip()
print(msg) # 不会改变原值
print(res) # 是产生了新值默认去掉的空格
msg='****egon****'
print(msg.strip('*'))了解：strip只取两边，不去中间
msg='****e*****gon****'
print(msg.strip('*'))
msg='**/*=-**egon**-=()**'
print(msg.strip('*/-=()'))应用
inp_user=input('your name>>: ').strip() # inp_user=" egon"
inp_pwd=input('your password>>: ').strip()
if inp_user == 'egon' and inp_pwd == '123':
print('登录成功')
else:
print('账号密码错误')4.1.6、切分split：把一个字符串按照某种分隔符进行切分，得到一个列表
默认分隔符是空格
info='egon 18 male'
res=info.split()
print(res)指定分隔符
info='egon:18:male'
res=info.split(':')
print(res)指定分隔次数(了解)
info='egon:18:male'
res=info.split(':',1)
print(res)4.1.7、循环
info='egon:18:male'
for x in info:
print(x)4.2 需要掌握
4.2.1、strip,lstrip,rstrip
msg='***egon****'
print(msg.strip('*'))
print(msg.lstrip('*'))
print(msg.rstrip('*'))4.2.2、lower,upper
msg='AbbbCCCC'
print(msg.lower())
print(msg.upper())4.2.3、startswith,endswith
print("alex is sb".startswith("alex"))
print("alex is sb".endswith('sb'))
4.2.4、format4.2.5、split,rsplit:将字符串切成列表
info="egon:18:male"
print(info.split(':',1)) # ["egon","18:male"]
print(info.rsplit(':',1)) # ["egon:18","male"]4.2.6、join: 把列表拼接成字符串
l=['egon', '18', 'male']
res=l[0]+":"+l[1]+":"+l[2]
res=":".join(l) # 按照某个分隔符号，把元素全为字符串的列表拼接成一个大字符串
print(res)
l=[1,"2",'aaa']
":".join(l)4.2.7、replace
msg="you can you up no can no bb"
print(msg.replace("you","YOU",))
print(msg.replace("you","YOU",1))4.2.8、isdigit
判断字符串是否由纯数字组成
print('123'.isdigit())
print('12.3'.isdigit())
age=input('请输入你的年龄：').strip()
if age.isdigit():
age=int(age) # int("abbab")
if age > 18:
print('猜大了')
elif age < 18:
print('猜小了')
else:
print('才最了')
else:
print('必须输入数字，傻子')4.3了解
4.3.1、find,rfind,index,rindex,count
msg='hello egon hahaha'找到返回起始索引
print(msg.find('e')) # 返回要查找的字符串在大字符串中的起始索引
print(msg.find('egon'))
print(msg.index('e'))
print(msg.index('egon'))找不到
print(msg.find('xxx')) # 返回-1，代表找不到
print(msg.index('xxx')) # 抛出异常
msg='hello egon hahaha egon、 egon'
print(msg.count('egon'))4.3.2、center,ljust,rjust,zfill
print('egon'.center(50,'*'))
print('egon'.ljust(50,'*'))
print('egon'.rjust(50,'*'))
print('egon'.zfill(10))4.3.3、expandtabs
msg='hello\tworld'
print(msg.expandtabs(2)) # 设置制表符代表的空格数为24.3.4、captalize,swapcase,title
print("hello world egon".capitalize())
print("Hello WorLd EGon".swapcase())
print("hello world egon".title())4.3.5、is数字系列
4.3.6、is其他
print('abc'.islower())
print('ABC'.isupper())
print('Hello World'.istitle())
print('123123aadsf'.isalnum()) # 字符串由字母或数字组成结果为True
print('ad'.isalpha()) # 字符串由由字母组成结果为True
print(' '.isspace()) # 字符串由空格组成结果为True
print('print'.isidentifier())
print('age_of_egon'.isidentifier())
print('1age_of_egon'.isidentifier())
num1=b'4' #bytes
num2=u'4' #unicode,python3中无需加u就是unicode
num3='四' #中文数字
num4='Ⅳ' #罗马数字
isdigit只能识别：num1、num2
print(num1.isdigit()) # True
print(num2.isdigit()) # True
print(num3.isdigit()) # False
print(num4.isdigit()) # False
isnumberic可以识别：num2、num3、num4
print(num2.isnumeric()) # True
print(num3.isnumeric()) # True
print(num4.isnumeric()) # True
isdecimal只能识别：num2
print(num2.isdecimal()) # True
print(num3.isdecimal()) # False
print(num4.isdecimal()) # False