Python编程：从入门到实践-用户输入和while循环

• 函数input() 

#!/usr/bin/env python
#-*- encoding:utf-8 -*-
name = input("Please enter your name: ")
print("Hello, " + name + "!")

• 使用int()来获取数值输入

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#!/usr/bin/env python #-*- encoding:utf-8 -*- age = input("How old are you? ") print(int(age))

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1 2	How old are you? 21 21

　　示例2：

#!/usr/bin/env python
#-*- encoding:utf-8 -*-
height = input("How old are you? ")
height = int(height)

if height >= 36:
  print("\nYou're tall enough to ride!")
else:
  print("\nYou'll be able to ride when you're a little older.")

• 求模运算符

 求模运算符（%），用来处理数值信息，它将两个数相除并返回余数

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>>> 4 % 3 1 >>> 5 % 3 2 >>> 6 % 3 0 >>> -7 % 3 2 >>>

 判断奇偶数

#!/usr/bin/env python
#-*- encoding:utf-8 -*-
number = input("Enter a number, and I'll tell you if it's even or odd: ")
number = int(number)
if number % 2 == 0:
  print("\nThe number " + str(number) + " is even.")
else:
  print("\nThe nuber " + str(number) + " is odd. ")

• 在Python2.7中获取输入

raw_input读取的内容以字符串的形式返回 

#!/usr/bin/env python
#-*- encoding:utf-8 -*-
msg = int(raw_input('How old are you? '))
print('I was ' + str(msg) + ' years old!')

How old are you? 22
I was 22 years old!

• while循环

 For循环用于集合中的每个元素都一个代码块，而while循环不断地运行，直到指定的条件不满足为止

#!/usr/bin/env python
#-*- coding: utf-8 -*-
#counting.py
current_number = 1
while current_number <= 5:
  print(current_number)
  current_number += 1

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""
使用while循环让程序再用户愿意时不断地运行，并定义一个退出值，
只用用户输入的不是这个值，程序就继续运行
"""
prompt = "\nTell me something, and I will repeat it back to you:"
prompt += "\nEnter 'quit' to end the program. "
message = ""
while message != 'quit':
  message = input(prompt)
  print(message)

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""
在上一个while基础上，修改。将单词'quit'消息不打印
"""
prompt = "\nTell me something, and I will repeat it back to you:"
prompt += "\nEnter 'quit' to end the program. "
message = ""
while message != 'quit':
  message = input(prompt)
  if message != 'quit':
    print(message) 

• 使用标志

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""
使用标志,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，
这个变量被成为标志，充当程序的交通信号灯。下列程序将标志命名为active
"""
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)

• 使用break、continue

在循环中使用break

#!/usr/bin/env python
#-*- coding: utf-8 -*-
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() + "!")

在循环中使用continue

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""从1数到10，只打印其中的偶数"""
current_number = 0
while current_number < 10:
  current_number += 1
  if current_number % 2 != 0:
    continue
  print(current_number)

• 避免无限循环

#!/usr/bin/env python
#-*- coding: utf-8 -*-
x = 1
while x <= 5:
  print(x)
  x += 1

#!/usr/bin/env python
#-*- coding: utf-8 -*-
"""当遗漏代码行x += 1,这个循环将一直运行"""
x = 1
while x <= 5:
  print(x)

• 使用while循环来处理列表和字典

 For循环是一个遍历列表的有效方式，但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。在遍历列表的同事对其进行修改，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。

　　示例：假设有一个列表，其中包含新注册但还未验证的网站用户；验证这些用户之后，将他们移动到另一个已验证用户列表中？方法是：利用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。

#!/usr/bin/env python
#-*- encoding: utf-8 -*-
#首先，创建一个待验证的用户列表和一个存储已验证用户的空列表
unconfirmed_users = ['alice', 'brain', 'candace']
confirmed_users = []
#验证每个用户，直到没有未验证用户位置，将每个经过验证的列表都移到已验证用户列表
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())

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C:\PyProjects>C:/Python37/python3.exe c:/PyProjects/demo.py Verifying user: Candace Verifying user: Brain Verifying user: Alice   The following users have been confirmed: Candace Brain Alice

  删除包含特定值的所有列表元素

#!/usr/bin/env python
#-*- encoding: utf-8 -*-
pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
print(pets)
while 'cat' in pets:
  pets.remove('cat')
print(pets)

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C:\PyProjects>C:/Python37/python3.exe c:/PyProjects/demo.py ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat'] ['dog', 'dog', 'goldfish', 'rabbit']

 使用用户输入来填充字典

#!/usr/bin/env python
#-*- encoding: utf-8 -*-
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 + ".")

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C:\PyProjects>C:/Python37/python3.exe c:/PyProjects/demo.py   What is your name? tianze Which mountain would you like to climb someday? panshan Would you like to let another person respond? (yes/no)yes   What is your name? tiandi Which mountain would you like to climb someday? xiangshan Would you like to let another person respond? (yes/no)no   ---Poll Results--- tianze  would like to climb panshan. tiandi would like to climb xiangshan.