2022-07-21 Python学习笔记9

一、总体计划：

开始时间：2022-07-13

计划完成时间：2022-08-12

计划每日完成量：15页/天，或0.7章/天

二、今日（2022-07-21）学习进度：

今日已学习24页，完成1章，日任务达标。

总体进度161页/460页，9章/20章。

三、学习笔记：

1、使用break 退出循环，要立即退出while 循环，不再运行循环中余下的代码，也不管条件测试的结果如何，可使用break 语句。break 语句用于控制程序流程，可使用它来控制哪些代码行将执行，哪些代码行不执行，从而让程序按你的要求执行你要执行的代码。

prompt = "\nPlease enter the name of a city you have visited:"  
prompt += "\n(Enter 'quit' when you are finished.) "
while True:      
    city = input(prompt)
    if city == 'quit':          
        break      
    else:          
        print("I'd love to go to " + city.title() + "!")

输出结果：
Please enter the name of a city you have visited:
(Enter 'quit' when you are finished.) New York
I'd love to go to New York!

Please enter the name of a city you have visited:
(Enter 'quit' when you are finished.) San Francisco
I'd love to go to San Francisco!

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

2、在循环中使用continue，要返回到循环开头，并根据条件测试结果决定是否继续执行循环，可使用continue 语句，它不像break 语句那样不再执行余下的代码并退出整个循环。

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

输出结果：
1
3
5
7
9

3、在列表之间移动元素，假设有一个列表，其中包含新注册但还未验证的网站用户；验证这些用户后，如何将他们移到另一个已验证用户列表中呢？一种办法是使用一个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，再将其加入到另一个已验证用户列表中。代码可能类似于下面这样：

# 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
#  将每个经过验证的列表都移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)
# 显示所有已验证的用户
print("\nThe following users have been confirmed:")
for confirmed_user in confirmed_users:
    print(confirmed_user.title())

输出结果：
Verifying user: Candace
Verifying user: Brian
Verifying user: Alice

The following users have been confirmed:
Candace
Brian
Alice

4、删除包含特定值的所有列表元素，假设你有一个宠物列表，其中包含多个值为'cat' 的元素。要删除所有这些元素，可不断运行一个while 循环，直到列表中不再包含值'cat' ，如下所示：

pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
print(pets)
while 'cat' in pets:
    pets.remove('cat')
print(pets)

输出结果：
['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
['dog', 'dog', 'goldfish', 'rabbit']

5、使用用户输入来填充字典，可使用while循环提示用户输入任意数量的信息。下面来创建一个调查程序，其中的循环每次执行时都提示输入被调查者的名字和回答。我们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：

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? ")
    # 将答卷存储在字典中
    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 + ".")

输出结果：
What is your name? Eric
Which mountain would you like to climb someday? Denali
Would you like to let another person respond? (yes/ no) yes

What is your name? Lynn
Which mountain would you like to climb someday? Devil's ThumbWould you like to let another person respond? (yes/ no) no

--- Poll Results ---
Lynn would like to climb Devil's Thumb.
Eric would like to climb Denali.