Python学习记录5：基础知识-用户输入和while循环

一、用户输入

1. 函数 .input() ：

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

函数input()接受一个参数；在这个示例中，python运行第一行代码时，用户将看到提示：
Tell me something, and I will repeat it back to you: 
程序等待用户输入，并在用户按回车键后继续运行。
输入存储在变量msg中，接下来的print（msg）将输入输出。

当必要的提示不止一行时，我们可以：

#先将部分提示存入一个变量，再使用+=运算符接上剩余的提示
prompt = "If you tell us who you are, we can personalize the messages you see."
prompt += "\nWhat is your first name? "

name = input(prompt)
print("\nHello, " + name + "!")

output：
If you tell us who you are, we can personalize the messages you see.
What is your first name? Ming

Hello, Ming!

2. 使用 int() 来获取数值输入：
   input会将输入理解为字符串，我们需要int来转换。将数值用于计算和比较前，务必将其转化为数值表示，避免不必要的错误。

height = input("How tall are you, in inches? ")
height = int(height) #转化为数值

if height >= 36:
    print("\nYou're tall enough to ride!")
else:
    print("\nYou'll be able to ride when you're a little older.")

3. 求模运算符：% （同c/c++）
   *python 2.7 中应使用: raw_input()来获取输入。

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二、while循环

1、简述：

prompt = "\nTell me something, and I will repeat it back to you:"
prompt += "\nEnter 'quit' to end the program. "
  
active = True #随便定义的一个标志变量
while active: #while的用法与c/c++类似，区别是不用括号
    message = input(prompt)
    
    if message == 'quit':
        active = False
    else:
        print(message)

*break/continue在python中的用法与c/c++中相同。

2、用while循环来处理列表和字典：

1. 在列表间移动元素：

#首先，创建一个待验证用户列表
#和一个用于存储已验证用户的空列表
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []

#验证每个用户，直到没有未验证用户为止
#将每个经过验证的用户都移动到已验证用户列表中
while unconfirmed_users:
    current_user = unconfirmed_users.pop()
    
    print("Verifying user: " + current_user.title())
    confirmed_users.append(current_user)
    
#显示所有已验证用户
print("\nThe following users have been confirmed:")
for confirmed_user in confirmed_users:
    print(confirmed_user.title())

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

The following users have been confirmed:
Candace
Brian
Alice

2. 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)

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

3. 使用用户输入来充填字典：

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? ")
    
    # 将答案存储在字典中
    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(name + " would like to climb " + response + ".")

output：
What is your name? 小明
Which mountain would you like to climb someday? 珠穆朗玛峰
Would you like to let another person respond? (yes/ no) yes

What is your name? 不告诉你
Which mountain would you like to climb someday? 也不告诉你
Would you like to let another person respond? (yes/ no) no

--- Poll Results ---
小明 would like to climb 珠穆朗玛峰.
不告诉你 would like to climb 也不告诉你.

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参考文献：《Python编程：从入门到实践》——【美】Eric Matthes