Python编程从入门到实践

第七章：用户输入和while循环

文章目录

• 第七章：用户输入和while循环
• • 7.1 函数input()的工作原理
  • • 7.1.1 编写清晰的程序
    • 7.1.2 使用int()获取数值输入
    • 7.1.3 求模运算符
  • 7.2 while 循环
  • • 7.2.1 使用while循环
    • 7.2.2 让用户选择何时退出
    • 7.2.3 使用标志
    • 7.2.4 使用break退出循环
    • 7.2.5 在循环中使用continue
    • 7.2.6 避免无限循环
  • 7.3 使用while循环处理列表和字典
  • • 7.3.1 在列表之间移动元素
    • 7.3.2 删除为特定值的所有列表元素
    • 7.3.3 使用用户输入来填充字典
  • 总结

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7.1 函数input()的工作原理

• 函数input()让程序暂停运行，等待用户输入一些文本。获取用户输入后，Python将其赋值给一个变量，以方便调用。

任务： 让用户输入文本，把文本呈现给用户

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 you.Hello python world！
Hello python world！

7.1.1 编写清晰的程序

• 使用input()时，应指定清晰易懂的提示，准确地指出希望用户提供什么样的信息
• 在提示末尾（冒号后面）包含一个空格，将提示与用户输入分开

name = input("Please enter your name: ")
print(f"nHello, {name}!")

Please enter your name: Tiya

Hello, Tiya!

#提示超过一行，可将提示赋给一个变量
prompt = "If you tell us who you are, we can personlize the message you see."
prompt += "nWhat is your first name? "  # +=的目的在前面字符串末尾附加一个字符串 

name = input(prompt)
print(f"nHello, {name}!")

If you tell us who you are, we can personlize the message you see.
What is your first name? Tiya

Hello, Tiya!

7.1.2 使用int()获取数值输入

• input()将用户输入解读为字符串

age = input("How old are you? ")

How old are you? 21

age >= 18

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
 in 
----> 1 age >= 18

TypeError: '>=' not supported between instances of 'str' and 'int'

• 解决办法：使用int()将字符串转化为数值表示

age = int(age)
age >=18

True

heigt = input("How tall are you, in inches? ")
heigt = int(heigt)

if heigt >= 48:
    print("nYou're tall enough to ride!")
else:
    print("nYou'll be able to ride when you're a little older." )

How tall are you, in inches? 71

You're tall enough to ride!

7.1.3 求模运算符

• 求模运算符（%）：将两个数相除并返回余数

任务： 判断一个数是奇数还是偶数

number = input("Enter a number, and I'll tell you if it's even or odd: " )
number = int(number)

if number % 2 == 0:
    print(f"nThe number {number} is even.")
else:
    print(f"nThe number {number} is odd.")

Enter a number, and I'll tell you if it's even or odd: 24729834

The number 24729834 is even.

7.2 while 循环

• for 循环：针对集合中每一个元素都执行一个代码块
• while循环：不断运行，直到指定的条件不满足

7.2.1 使用while循环

任务： 打印1-5

current_number = 1
while current_number <= 5:
    print(current_number)
    current_number += 1

1
2
3
4
5

7.2.2 让用户选择何时退出

任务： 定义一个退出值， 只要用户不输入这个值，程序将继续运行

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

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

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

prompt = "nTell me something,and I will repeat it back to you: "
prompt += "nEnter 'quit' to end the program."

message = ""

while message != 'quit':
    message = input(prompt)
    
    if message != 'quit': #仅在消息不是quit时打印
        print(message)

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

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

7.2.3 使用标志

• 多个不同的事件导致程序停止运行退出
• 定义一个变量（标志，flag），用于判断整个程序是否处于活动状态
• 程序在标志为True时继续，在任何事件导致标志值为False时程序停止
• while语句中只需检查一个条件：标志的当前值是否为True，然后将其他测试都放在其他地方
• 在复杂程序中，标志很有用——在任意时间导致活动标志变成False时，主游戏循环将退出，此时可以显示一条游戏结束信息，并让用户选择是否要重玩

prompt = "nTell me something,and I will repeat it back to you: "
prompt += "nEnter 'quit' to end the program."

active = True
while active:
    message = input(prompt)
    
    if message == 'quit': #仅在消息不是quit时打印
        active = False
    else:
        print(message)

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

7.2.4 使用break退出循环

• break——立即退出while循环，不再运行循环中剩余的代码，也不管条件测试的结果
• 在任何循环中都可以使用break语句

prompt = "nPlease enter the name of a city you have visited: "
prompt += "nEnter 'quit' when you finished."

 
while True:
    city = input(prompt)
    
    if city == 'quit': #仅在消息不是quit时打印
        break
    else:
        print(f"I'd love to go to {city.title()}.")

Please enter the name of a city you have visited: 
Enter 'quit' when you finished.sdflk
I'd love to go to Sdflk.

Please enter the name of a city you have visited: 
Enter 'quit' when you finished.s
I'd love to go to S.

Please enter the name of a city you have visited: 
Enter 'quit' when you finished.df
I'd love to go to Df.

Please enter the name of a city you have visited: 
Enter 'quit' when you finished.quit

7.2.5 在循环中使用continue

• break——立即退出while循环，不再运行循环中剩余的代码，也不管条件测试的结果
• continue——返回循环开头，并根据条件测试的结果决定是否继续执行循环

任务： 只打印1-10中的奇数

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

1
3
5
7
9

7.2.6 避免无限循环

• 每个while循环都必须有停止运行的途径

x = 1
while x <= 5:
    print(x)
    x += 1

1
2
3
4
5

# 无限循环，不要尝试，可按ctrl+C终止程序
#x = 1
#while x <= 5:
#    print(x)
    

7.3 使用while循环处理列表和字典

• for循环可有效的遍历列表，但不适合修改列表，会导致Python难以跟踪其中的元素
• 要在遍历列表的同时对其元素修改，可以使用while循环

7.3.1 在列表之间移动元素

任务： 假设一个列表包含新注册但还未验证的用户，验证这些用户后，如何将其移到另一个已验证用户列表中

• 使用while循环，在验证用户的同时将其从未验证用户列表中提取出来，再将其加入另一个已验证用户列表中

unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []

#验证每个用户，直到没有未验证用户为止，将每个验证用户移到已验证用户列表中
while unconfirmed_users:
    current_user = unconfirmed_users.pop()
    
    print(f"Verifying user: {current_user.title()}")
    confirmed_users.append(current_user)
    
#显示所有已验证用户
print(f"nThe following users have been confirmed:")
for confirmed_user in confirmed_users:
    print(confirmed_user.title())

Verifying user: Candace
Verifying user: Brian
Verifying user: Alice

The following users have been confirmed:
Candace
Brian
Alice

7.3.2 删除为特定值的所有列表元素

• remove()一次只能删除一个特定值
• 在while 循环使用remove()，直到列表中不再包含特定元素

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']

7.3.3 使用用户输入来填充字典

任务： 创建一个调查程序，其中循环每次执行时都提示输入被调查者的名字的回答，将收集的数据存储在一个字典中，以便将回答同被调查者关联起来

#设置一个空字典
responses = {}

#设置一个标志，指出调查是否继续
polling_active = True

while polling_active:
    #提示输入被调查者的名字和回答
    name = input("nWhat is your name? ")
    response = input("Which mountain would you like to climb someday?")
    
    #将回答存储在字典中
    responses[name] = response
    
    #看看是否还有人要参与调查
    repeat = input("Would you like to let another person respond? (yes/no)")
    if repeat == 'no':
        polling_active = False
    
    #调查结束，显示结果
    print("n---Poll Results---")
    for name, response in responses.items():
        print(f"{name} would like to climb {response}.")

What is your name? sdf
Which mountain would you like to climb someday?fsdfsg
Would you like to let another person respond? (yes/no)yes

---Poll Results---
sdf would like to climb fsdfsg.

What is your name? jh
Which mountain would you like to climb someday?fhg
Would you like to let another person respond? (yes/no)no

---Poll Results---
sdf would like to climb fsdfsg.
jh would like to climb fhg.

总结

暑期编程PK赛 得CSDN机械键盘等精美礼品！