字符串/与之操作

Posted 2021-03-06 tornadoes-destroy-parking-lots

定义：在单引号双引号三引号内包含一串字符

name1 = ‘jason‘  # 本质:name = str(‘任意形式内容‘)
name2 = "lili"  # 本质:name = str("任意形式内容")
name3 = """ricky"""  # 本质:name = str("""任意形式内容""")

　字符串的类型转换

# 数据类型转换：str()可以将任意数据类型转换成字符串类型，例如 
>>> type(str([1,2,3])) # list->str
<class ‘str‘>
>>> type(str({"name":"jason","age":18})) # dict->str
<class ‘str‘>
>>> type(str((1,2,3)))  # tuple->str
<class ‘str‘>
>>> type(str({1,2,3,4})) # set->str
<class ‘str‘>

　　

字符串中的操作！！！优先掌握！！！

# 1.按索引取值（正向取+反向取）：只能取
msg = ‘hello world‘
# 正向取
print(msg[0])
# 反向去
print(msg[-1])
# 只能取
msg[0]=‘H‘ # 报错

# 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]
print(res)
# 步长：默认步长为1
res = msg[0:5:2] # 0,2,4
print(res) # hlo
# 反向步长
res = msg[5:0:-1]
print(res) # " olle"

res = msg[:] # res=msg[0:11]
print(res)

res = msg[::-1] # 把字符串倒过来
print(res)

# 3.长度len
msg = ‘hello world‘
print(len(msg))

　　

# 4.成员运算in和not in
# 判断子字符串是否存在于一个大字符串中
print(‘love‘ in ‘I love you‘)
print(‘love‘ not in ‘love you‘)

# 5.移除字符串左右两侧的符号strip()
# 了解：strip只去两边字符，不去中间
msg = ‘**lo*ve**‘
res = msg.strip(‘*‘) # 默认去掉左右两侧空格
print(msg) # 不会改变原值
print(res) # 是产生了新值

# 应用
‘‘‘
name = input(‘name:‘).strip()
pwd = input(‘password:‘).strip()
if name == ‘zcy‘ and pwd == ‘123‘:
    print(‘登录成功‘)
else:
    print(‘登录失败‘)
‘‘‘

# 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
# 默认按照空格分隔
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) # [‘egon‘, ‘18:male‘]

# 7.循环
info = ‘egon:18:male‘
for i in info.split(‘:‘):
    print(i)

　　

需要掌握的！！

# 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、format

#4.2.5、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‘)

　　

***了解即可***
#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	world‘
# print(msg.expandtabs(2)) # 设置制表符代表的空格数为2

#4.3.4、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



# isnumeric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



>>> l=[1,2,3,4,5,6]
>>> l[0:3:1] 
[1, 2, 3]  # 正向步长
>>> l[2::-1] 
[3, 2, 1]  # 反向步长

# 通过索引取值实现列表翻转
>>> l[::-1]
[6, 5, 4, 3, 2, 1]