Python基础知识用户输入与while循环

Posted 2020-12-17 Carl39

用户输入

　　使用input()函数可获取用户输入的文本，并以字符串的形式存入变量中。

name = input( "Please enter your name: " )
print( "Hello, " + name + "!" )

当输入Carl时的输出：

Please enter your name: Carl
Hello, Carl!

 

　　有时候，输入提示可能超过一行，此时可将提示存储在一个变量中，再将该变量传递给函数input()。

　　下例就是使用+=运算符创建多行字符串的一种方式（可理解为字符串的拼接）。

prompt = "Please tell us who you are."
prompt += "
What‘s your first name? "

name = input( prompt )
print( "
Hello, " + name + "!" )

 

　　由于Python将用户输入解读为字符串，所以当要让Python将输入视为数值时，需要调用int()函数。

age = input( "How old are you?" )    ‘‘‘输入19‘‘‘
age = int( age )
age >= 18    ‘‘‘True‘‘‘

 

while循环

1、简单的while循环

current_number = 1
while current_number <= 5:
    print( current_number )
    current_number += 1

输出为：

1
2
3
4
5

 

　　在要求很多条件都满足才能继续运行的程序中，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。当标志的值为True时，程序可继续进行；当标志的值为False时，程序停止运行。

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

active = True
while active:
    message = input( prompt )
    
    if message == ‘quit‘:
         active = False
    else:
        print( message )

 多次输入，得到输出为：

Tell me something, and I will repeat it back to you:
Enter ‘quit‘ to end the program. City
City
Tell me something, and I will repeat it back to you:
Enter ‘quit‘ to end the program. Both
Both
Tell me something, and I will repeat it back to you:
Enter ‘quit‘ to end the program. quit

 

2、break语句

　　在循环中使用break语句，可直接退出循环。

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

while True:
    message = input( prompt )
    
    if message == ‘quit‘:
        break
    else:
        print( message )

 

3、continue语句

　　在循环中使用continue语句，可让程序跳过在循环体中位于continue语句后面的所有语句，直接回到循环开始并开始下一轮的循环。

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

输出为：

1
3
5
7
9

 

使用while循环处理列表和字典

1、在列表之间移动元素

‘‘‘验证用户‘‘‘
unconfirmed_users = [ ‘alice‘ , ‘brian‘ , ‘candance‘ ]
confirmed_users = [ ]

‘‘‘逐一验证用户‘‘‘
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（ "
The following users have been confirmed: " )
for confirmed_user in confirmed_users:
    print( confirmed_users.title() )

　　（运行时删除中文注释，其他程序同）

 

2、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 )

输出为：

[‘dog‘, ‘cat‘, ‘dog‘, ‘goldfish‘, ‘cat‘, ‘rabbit‘, ‘cat‘]
[‘dog‘, ‘dog‘, ‘goldfish‘, ‘rabbit‘]

 

3、将输入存储进字典

responses = { }

‘‘‘设置标志‘‘‘
polling_active = True

while polling_active:
    ‘‘‘获取需要加入字典的键-值对信息‘‘‘
    name = input( "
What‘s your name? " )
    response = input( "which mountain would you like to climb someday?" )
    
    ‘‘‘将键-值对录入字典‘‘‘
    responses[ name ] = response
    
    ‘‘‘是否要执行下一轮循环‘‘‘
    repeat = input( "Asking another person?(yes/no)" )
    if repeat == ‘no‘:
        polling_active = False

‘‘‘调查结束，显示结果‘‘‘        
print( "
--- Poll Results ---" )
for name, response in responses.items():
    print( name + " would like to climb " + response + "." )

输入一些信息，得到输出为：

What‘s your name? Eric
which mountain would you like to climb someday?Denali
Asking another person?(yes/no)yes

What‘s your name? Lynn
which mountain would you like to climb someday?Devil‘s Thumb
Asking another person?(yes/no)no

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

 

参考书籍：《Python编程：从入门到实践》

2020-07-12