python学习（七）下while循环

while循环简介

• for循环用于针对集合中的每个元素的一个代码块，
• while循环是不断的运行，直到指定的条件不满足为止。

使用while循环

• while循环从1到5

current_number = 1
while current_number <= 5:
    print(current_number)
    current_number += 1
    
1
2
3
4
5

让用户何时选择退出

• 定义一个退出值，只要用户输入发热不是这个值，程序就一直运行。

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

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

***Repl Closed***

使用标志

• 要求很多条件都满足才继续运行的程序，可定义一个变量，用于判断一个程序是否属于一个活动状态，
• 这个变量被称之为标志。

prompt = ("\nTell me something,and I will repeart 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)
        
Tell me something,and I will repeart it back to you: 
Enter 'quit' to end the program.aa
aa

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

***Repl Closed***

• 标识很有用，在任何事件导致活动标记为False时，while循环将会退出。

使用break退出循环

• break语句用于控制程序流程。
• 使用break语句，立即退出while循环，不在运行循环中余下的代码。

prompt = '\nPlease enter the name of a city you have citiies:'
prompt += "\n(Enter 'quit' when you are finished.)"

while True:
    city = input(prompt)
    if city == 'quit':
        break
        
Please enter the name of a city you have citiies:
(Enter 'quit' when you are finished.)beijing

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

***Repl Closed***

在while循环中使用continue

• 使用continue语句，返回到循环开头，并根据循环条件测试结果是否继续执行循环。

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

    print(current_number)

1
3
5
7
9
11

避免无限循环

• 要避免编写无限循环，务必对每个while循环进行测试，确保他按照预期那样结束。

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，for循环中不应修改列表，否则将导致python难以追踪其中元素。
• 要遍历列表并对其进行修改，使用while循环。

unconfirmed_user = ['alice','brian','candace']
confirmed_user = []
while unconfirmed_user:
    current_user = unconfirmed_user.pop()
    print("Verifying user: " + current_user.title())
    confirmed_user.append(current_user)
    
Verifying user: Candace
Verifying user: Brian
Verifying user: Alice
[Finished in 0.4s]

删除包含特定值的所有列表元素

• 使用函数remove()来删除列表中的特定值。

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']

使用用户输入来填充字典

• 定义一个空字典，并设置一个标记。

responses = {}
polling_active = True

while polling_active:
    name = input("\nWhat is your name: ")
    respone = input("\nwhich mountain would you like to climb someday? ")
    responses[name] = respone
    repeat = input("\nWould you like to let another person respond?(yes/no)")
    if repeat == 'no':
        polling_active = False

print("\n----POLL Results----")
for name, respone in responses.items():
    print(name + " wonld like to climb " + respone + ".")
    

What is your name: alice

which mountain would you like to climb someday? aa

Would you like to let another person respond?(yes/no)yes

What is your name: nana

which mountain would you like to climb someday? bb

Would you like to let another person respond?(yes/no)no

----POLL Results----
alice wonld like to climb aa.
nana wonld like to climb bb.

***Repl Closed***

总结

• 使用input()来获取用户的输入信息。
• 如何处理文本和数字输入。
• 如何使用while循环安装用户的要求不断运行。
• 多种控制while循环的方式。
• 设置获取标志