按索引取值

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# 按索引取值
msg = 'hello world'
print(msg[1])  # 正向取
print(msg[5])  # 空也可以取
print(msg[-1])  # 反向取
# 只能取不可以改
res = msg[1] == 'H'
print(res)  # False

切片

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# 取头不取尾
msg = 'hello world'
res = msg[0:5]
print(res)  # hello
print(msg)  # hello world
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# 取头不取尾
msg = 'hello world'
res = msg[0:5:2]
print(res)  # hlo
print(msg)  # hello world

.strip()相关知识

.strip()只可以去两边

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msg = '     bage       '
res = msg.strip()
print(res)  # bage

msg = '*****bage*****'
print(msg.strip('*'))  # bage

# 只去两边，不去中间
msg = '****ba****ge****'
print(msg.strip('*'))  # ba****ge


msg = '-=*&bage-=-'  # bage
print(msg.strip('=-*&'))

.lstrip()只可以左去边

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msg = '     bage       '
res = msg.lstrip()  # bage
print(res)
# 只去左边
msg = '*****bage*****'  # bage*****
print(msg.lstrip('*'))

# 只去左边
msg = '****ba****ge****'  # ba****ge****
print(msg.lstrip('*'))

.rstrip()只可以右去边

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# 只去右边
msg = '     bage       '
res = msg.rstrip()  #      bage
print(res)
# 只去右边
msg = '*****bage*****'  # *****bage
print(msg.rstrip('*'))

# 只去右边
msg = '****ba****ge****'  #****ba****ge
print(msg.rstrip('*'))

.strip的应用
当用户输入空格时，不影响操作

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uers = input('请输入姓名：').strip()
pwd = input('请输入密码：').strip()
if uers == 'bage' and pwd == '123':
    print('登入成功')
else:
    print('姓名或密码错误')

.split()相关知识

可以把字符串切分为列表

.split()

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# 默认根据空格切分
sp = 'my name is bage'
print(sp.split())

# 指定符号切分
sp = 'my:name:is:bage'
print(sp.split(':'))

# 指定切分次数
sp = 'my:name:is:bage'
print(sp.split(':', 1))

# 循环
sp = 'my:name:is:bage'
for x in sp:
    print(x)

.rsplit()

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# 指定切分次数，从右往左
sp = 'my:name:is:bage'
print(sp.rsplit(':', 1))  # ['my:name:is', 'bage']

lower与upper相关知识

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name = 'bAGe'
print(name.lower())  # bage
print(name.upper())  # BAGE

.join相关知识

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l = ["bage",'19','play']
ress = l[0] + ':' + l[1] + ':' + l[2]  #傻子才用
res = ':'.join(l)  #根据分隔符将列表合并为字符串（只限列表里面为字符串）
print(ress)
print(res)

.replace替换 相关知识

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msg = 'my name is bage my name is bage'
print(msg.replace('my', 'MY'))  # 替换
print(msg.replace('my', 'MY', 1))  # 指定替换

.isdigit相关知识

判断字符串是否全为数字组成

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age = input('猜猜我我的年龄：').strip()
if age.isdigit():
    age = int(age)
    if age > 19:
        print('太大了')
    elif age < 19:
        print('太小了')
    elif age == 19:
        print('太牛了，你猜对了')
else:
    print('输数字，傻子')