python——用户和while循环

第七章：用户和while循环

7.1 函数input的工作原理

# 函数input使程序暂停运行，等待用户输入一些文本。获取用户输入之后，python将其存储在一个变量之中。
# input（）接受一个参数：要向用户显示的提示或说明，让用户了解该怎么做。
message = input("Tell me something, and i will repeat it back to you")
print(message)

Tell me something, and i will repeat it back to youhui
hui

# 对于以上问题，我们需要将字符串类型的变量转化为int。
age = input("Please input your age :")
age = int(age)
if age < 12:
    print("you are a child")
else:
    print("you are not a child")

Please input your age :15
you are not a child

7.2 while循环

# for循环用于针对集合中的每个元素都有一个代码块，而while循环不断地运行，直到指定的条件不再满足。
# 利用while循环数数
# 当数据大于10的时候，停止输出
current_number = 1
while current_number <= 10:
    print(current_number)
    current_number += 1
    

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# 我们可以自定义何时退出循环
prompt = "Tell me something, and i will repeat it to you !"
prompt += "you can enter 'quit' to end the program"
message = ""
while message != 'quit':
    message = input(prompt)
    print(message)

Tell me something, and i will repeat it to you !you can enter 'quit' to end the programhui
hui
Tell me something, and i will repeat it to you !you can enter 'quit' to end the programquit
quit

# 使用break退出循环
# 要立即退出循环，不再运行循环中的代码，也不管测试的条件如何，可以使用break语句
prompt = "Please enter the name of a city that you have visited !"
prompt += "Enter 'quit' to end the program"
while True:
    city = input(prompt)
    if city == 'quit':
        break
    else:
        print("I would like to go to "+city+" !")

Please enter the name of a city that you have visited !Enter 'quit' to end the programhenan
I would like to go to henan !
Please enter the name of a city that you have visited !Enter 'quit' to end the programquit

# 若使程序返回到循环开头，并根据测试结果决定是否继续执行循环，可使用continue语句，它不像break语句不再执行余下的代码而是返回
#到循环开头
# 执行continue语句时，使代码返回到循环开头！！！
current_num = 0
while current_num < 10:
    current_num += 1
    if current_num % 2 ==0:
        continue
    print(current_num)

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# 一定要避免无线循环！！
x = 1
while x < 10:
    print(x)
    x += 1
# 如果遗漏 x += 1,程序会进入无线循环

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7.3 使用while循环处理列表和字典

# for循环是一种遍历列表的有效方式，但是在for循环中不应修列表，否则将导致python难以跟踪其中的元素。
# 若需要在遍历列表的同时对列表进行修改，可以使用while循环
# 设存在一个列表，其中包含新注册的用户，验证这些用户，将其移到已验证的用户列表。
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []
while unconfirmed_users:
    current_user = unconfirmed_users.pop()
    print("Verfying user:"+current_user.title())
    confirmed_users.append(current_user)
print("The following user has been confirmed:")
for user in confirmed_users:
    print(user.title())

Verfying user:Candace
Verfying user:Brian
Verfying user:Alice
The following user has been confirmed:
Candace
Brian
Alice

# remove()用来删除某个特定元素，但是如果该元素存在不止一次，就需要和while循环结合
# 删除包含特定值的所有列表元素
pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
print(pets)

while 'cat' in pets:
    pets.remove('cat')
print(pets)

['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
['dog', 'dog', 'goldfish', 'rabbit']

# 可使用while提示用户输入，并将用户的输入存储在一个字典中
responses= {}
polling_active = True
while polling_active:
    name = input("what is your name ? ")
    response = input("which mountain would you like to climb ?")
    responses[name] = response
    repeat = input("Would you like to let other person respond ? (yes / no)")
    if repeat == 'yes':
                 polling_active = True
    
print("\n--- poll result ---")
for name, response in responses.items():
                 print(name + " would like to climb " + response)

what is your name ? hui
which mountain would you like to climb ?yellow mountain
Would you like to let other person respond ? (yes / no)ji

--- poll result ---
hui would like to climb yellow mountain

# 梦想的度假胜地
# 编写一个程序，调查用户梦想的度假旅游胜地，并将调查结果打印显示
response = {}
polling_active = True
while polling_active:
    name = input("Can you tell me your name ?")
    place = input("Would you like tell me which place you want go ?")
    response[name] = place
    message = input("would you like another person answer this question ?(yes/no) ")
    if message == "yes":
        polling_active = True
    else:
        polling_active = False
        
for name, place in response.items():
    print(name+" would like to go "+place)
    

Can you tell me your name ?hui
Would you like tell me which place you want go ?beijing
would you like another person answer this question ?(yes/no) no
hui would like to go beijing

练习

1、餐馆订位：编写一个程序，询问多少人用餐，如果超过8人，打印一条消息指出没有空桌，否则指出有空桌!
2、电影票：有家电影院根据观众的年龄收取不同的票价；不到3岁的观众免费；3-12岁的观众10，美元；超过12岁的观众15美元。请编写一个循环，询问观众的年龄，并指出票价。
3、熟食店：创建一个名为sandwich_orders的列表，在其中包含各种三明治的名字；再创建一个名为finished_sandwiches的空列表。遍历列表sandwich_orders，对于每种三明治都打印出一条消息：如：I made your tuna sandwich.并将其移到列表finished_sandwiches。所有三明治都做好之后，打印一条消息，将这些三明治列出来。