《python crash course》笔记(4)

1. 用户输入

  1.1 input()

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

     input()接受一个参数，用来向用户的显示或说明，然后用户输入内容，以string(字符串)的形式存储到message变量中，并且以         回车结束，下面看一个高级一点的例子

prompt = "If you tell us who you are, we can personalize the messages you see." 
prompt += "
What is your first name? " 
name = input(prompt) 
print("
Hello, " + name + "!") 

     输出为

If you tell us who you are, we can personalize the messages you see.  

What is your first name? Eric  
Hello, Eric! 

  1.2 int()

     获取数值输入用Int()而非input()

height = input("How tall are you, in inches? ") 
height = int(height) 
if height >= 36: 
   print("
You're tall enough to ride!") 
else: 
    print("
You'll be able to ride when you're a little older.")

     输出如下

How tall are you, in inches? 71
You're tall enough to ride!

2. while循环

  2.1 简单例子

current_number = 1
while current_number <= 5: # 注意加上冒号！
    print(current_number)
    current_number += 1

     输出结果如下

1
2
3
4
5

    注意使用while循环一个典型的逻辑错误就是自增表达式的位置问题，如下

current_number = 1
while current_number <= 5: # 注意加上冒号！
    current_number += 1
    print(current_number)

    这种情况输出如下

2
3
4
5
6

  2.2 让用户选择何时退出

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

message='' # define a string
while message != 'quit':
    message = input(prompt)    
    print(message) 

    但这样会把quit也打印出来，改善方法就是加个if语句判断

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

message='' # define a string
while message != 'quit': # 注意加冒号(colon)
    message = input(prompt)
    if message != 'quit': # 注意加冒号   
        print(message) 

  2.3 使用标志(flag)

prompt = "
Tell me something, and I will repeat it back to you:"
prompt += "
Enter 'quit' to end the program. "
  
active = True # define a flag
while active:
    message = input(prompt)
    if message == 'quit':
        active = False
    else:
        print(message)

  2.4 使用break

prompt = "
Please tell me a city you have visited:"
prompt += "
(Enter 'quit' when you are finished.) "

while True:
    city = input(prompt) 
    if city == 'quit':
        break          # 执行break后会立即退出while循环
    else:
        print("I'd love to go to " + city.title() + "!")

 2.5 使用break

current_number = 0
while current_number < 10:
    current_number += 1
    if current_number %2 == 0:
        continue      # 执行continue后将忽略循环中剩下的代码而开继续新的循环
    print(current_number)

    输出结果如下

1
3
5
7
9

  2.6 使用while循环处理列表和字典

    2.6.1 在列表之间移动元素

unconfirmed_users=['alice','brian','candace']
confirmed_users=[]
while unconfirmed_users:
    current_user=unconfirmed_users.pop()
    print("Verifying user: "+current_user.title())
    confirmed_users.append(current_user)
print("
The following users have been confirmed:") 
for confirmed_user in confirmed_users: 
    print(confirmed_user.title())

  2.6.2 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)

  2.6.3 使用用户输入来填充字典

responses = {}

# Set a flag to indicate that polling is active.
polling_active = True

while polling_active:
    # Prompt for the person's name and response.
    name = input("
What is your name? ")
    response = input("Which mountain would you like to climb someday? ")
    
    # Store the response in the dictionary:
    responses[name] = response
    
    # Find out if anyone else is going to take the poll.
    repeat = input("Would you like to let another person respond? (yes/ no) ")
    if repeat == 'no':
        polling_active = False
        
# Polling is complete. Show the results.
print("
--- Poll Results ---")
for name, response in responses.items():
    print(name + " would like to climb " + response + ".")