1函数 input()的工作原理
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将其存储在一个变量中
1.1编写清晰的程序
有时候，提示可能超过一行，例如，你可能需要指出获取特定输入的原因。在这种情况下，可将提示存储在一个变量中，再将该变量传递给函数input()
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 + "!")
If you tell us who you are, we can personalize the messages you see.
What is your first name? Eric
Hello, Eric!
1.2使用 int()来获取数值输入
1.3求模运算符（%）
将两个数相除并返回余数
6 % 3
0
7 % 3
1
1.4在 Python 2.7 中获取输入
2while 循环简介
2.1使用 while 循环
2.2让用户选择何时退出
2.3使用标志
在更复杂的程序中，很多不同的事件都会导致程序停止运行；在这种情况下，该怎么办呢？
导致程序结束的事件有很多时，如果在一条while语句中检查所有这些条件，将既复杂又困难。
在要求很多条件都满足才继续运行的程序中，可定义一个变量，用于判断整个程序是否处于活动状态。这个变量被称为标志，充当了程序的交通信号灯。你可让程序在标志为True时继续运行，并在任何事件导致标志的值为False时让程序停止运行。这样，在while语句中就只需检查一个条件——标志的当前值是否为True，并将所有测试（是否发生了应将标志设置为False的事件）都放在其他地方，从而让程序变得更为整洁
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':
active = False
else:
print(message)
2.4使用 break 退出循环
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() + "!")
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
2.5在循环中使用 continue
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
current_number = 0
while current_number < 10:
current_number += 1
if current_number % 2 == 0:
continue
print(current_number)
1
3
5
7
9
2.6避免无限循环
x = 1
while x <= 5:
print(x)
x += 1
如果程序陷入无限循环，可按Ctrl + C，也可关闭显示程序输出的终端窗口
3使用 while 循环来处理列表和字典
for循环是一种遍历列表的有效方式，但在for循环中不应修改列表，否则将导致Python难以跟踪其中的元素。要在遍历列表的同时对其进行修改，可使用while循环。通过将while循环同列表和字典结合起来使用，可收集、存储并组织大量输入，供以后查看和显示
3.1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。
# 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())
Verifying user: Candace
Verifying user: Brian
Verifying user: Alice
The following users have been confirmed:
Candace
Brian
Alice
3.2删除包含特定值的所有列表元素
pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
while 'cat' in pets:
pets.remove('cat')
print(pets)
['dog', 'dog', 'goldfish', 'rabbit']
3.3使用用户输入来填充字典
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 + ".")
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 Thumb
Would 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.
