python进阶(3)--条件判断、用户输入

文档目录：

一、if语句
二、检索条件
三、用户输入input
四、while+inoput(),让用户选择何时退出
五、break与continue
六、while循环处理字典和列表

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一、if语句

1、if-else语句

cars=['audi','bmw','toyota']
for car in cars:
    if car=='bmw':
        print(car.upper())
    else:
        print(car.title())

查看结果：

Audi
BMW
Toyota

2、if-elif-else

age=12
if(age<4):
    print("Your admission cost is $0.")
elif(age<18):
    print("Your admission cost is $25.")
else:
    print("Your admission cost is $40.")

查看结果：

Your admission cost is $25.

二、检索条件

1、忽略大小写

car='Audi'
print(car=='audi')
print(car.lower()=='audi')
print(car.upper()=='AUDI')

查看运行结果：

2、检查不相等

car='Audi'
print(car !='AUDI')

查看运行结果：

True

3、检查多个条件

age_0=22
age_1=18
print(age_0>=21 and age_1>=21)
print((age_0>=21) and (age_1<21))
print(age_0>=21 or age_1>=21)

查看运行结果：

False
True
True

4、检查特定值是否包含在列表中

testList=['A','B','C']
print('A' in testList)
print('D' not in testList)

查看运行结果：

True
True

5、检查列表是否为空

testList2=[1,2,3]
testList3=[]
if testList2:
    for test in testList2:
        print(test)
    else:
        print("testList2为空")
if testList3:
    for test in testList2:
        print(test)
    else:
        print("testList3为空")

查看运行结果：

1
2
3
testList2为空

三、用户输入input

1、用户输入并返回

message=input("Tell me something,and I will repeat it back to you:")
print(message)

查看结果：

Tell me something,and I will repeat it back to you:hello world
hello world

2、f表达式返回

name=input("Please enter yout name:")
print(f"hello,{name}!")

查看结果：

Please enter yout name:jack
hello,jack!

3、更长的句子

prompt="Tell me something,and I will repeat it back to you,"
prompt+="\nWhat's your name?\n"
name=input(prompt)
print(f"hello {name.title()}")

查看结果：

Tell me something,and I will repeat it back to you,
What's your name?
mary
hello Mary

4、int()获取数值输入

age=input("How old are you？:")
age=int(age)
print(f"Your age is {age}!")

查看结果：

How old are you？:27
Your age is 27!

四、while+inoput(),让用户选择何时退出

1、普通用法

prompt="Tell me something,and I will repeat it back to you:"
prompt+="\nEnter 'quit' to be end the program."
message=""
while message!='quit':
    message=input(prompt)
    if message!='quit':
        print(message)

查看结果

Tell me something,and I will repeat it back to you:
Enter 'quit' to be end the program.hello world
hello world
Tell me something,and I will repeat it back to you:
Enter 'quit' to be end the program.quit

2、进阶用法

prompt="Tell me something,and I will repeat it back to you:"
prompt+="\nEnter 'quit' to be end the program."
#设置标志
active=True
while active:
    message=input(prompt)
    if message=='quit':
        active=False
    else:
        print(message)

查看结果：

Tell me something,and I will repeat it back to you:
Enter 'quit' to be end the program.ok
ok
Tell me something,and I will repeat it back to you:
Enter 'quit' to be end the program.quit

五、break与continue

1、break：退出循环

prompt="Tell me a city you want got to."
prompt+="\nEnter 'quit' to be end the program:"
while True:
    city=input(prompt)
    if city=='quit':
        break
    else:
        print(f"You love to go to {city.title()}!")

查看结果：

Tell me a city you want got to.
Enter 'quit' to be end the program:nanjing
You love to go to Nanjing!
Tell me a city you want got to.
Enter 'quit' to be end the program:newyork
You love to go to Newyork!
Tell me a city you want got to.
Enter 'quit' to be end the program:quit

2、continue：跳出本次循环，继续执行

current_number=0
while current_number<10:
    current_number+=1
    if current_number%2==0:
        continue
    else:
        print(current_number)

查看结果：

1
3
5
7
9

六、while循环处理字典和列表

1、while+列表：用户认证

#处理用户认证的列表
unconfirmed_users=['alice','brian','candace']
confirmed_users=[]
while unconfirmed_users:
    current_user=unconfirmed_users.pop()
    print(f"Verfying users:{current_user.title()}")
    confirmed_users.append(current_user)
#显示所有验证的用户
print("\nThe following users have been confirmed!")
for confirm_user in confirmed_users:
    print(confirm_user.title())

查看结果

Verfying users:Candace
Verfying users:Brian
Verfying users:Alice

The following users have been confirmed!
Candace
Brian
Alice

2、删除特定值的所有列表元素

pet=['dog','cat','pig','cat','triger','rabbit']
print(f"删除前:{pet}")
while 'cat' in pet:
    pet.remove('cat')
print(f"删除后：{pet}")

查看结果：

删除前:['dog', 'cat', 'pig', 'cat', 'triger', 'rabbit']
删除后：['dog', 'pig', 'triger', 'rabbit']

3、使用字典记录问卷调差

mydict={}
active=True
while active:
    name=input("Please enter your name:")
    city=input("Please enter what city you want go to:")
    mydict[name]=city
    next=input("Do you want to send this questionnaire to another people(yes/no):")
    if next=='no':
        break
print("The questionnaire is over,now the result is:")
for name,city in mydict.items():
    print(f"{name.title()} want go to {city.title()}!")

查看结果：

Please enter your name:lily
Please enter what city you want go to:nanjing
Do you want to send this questionnaire to another people(yes/no):yes
Please enter your name:mary
Please enter what city you want go to:shanghai
Do you want to send this questionnaire to another people(yes/no):yes
Please enter your name:tom
Please enter what city you want go to:london
Do you want to send this questionnaire to another people(yes/no):no
The questionnaire is over,now the result is:
Lily want go to Nanjing!
Mary want go to Shanghai!
Tom want go to London!