Python学习（九）while 循环

while循环简介

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

使用while循环

while数数，从1-5

current = 1

while current <= 5 :

print(current)

current += 1

1
2
3
4
5

用户选择何时退出

标志：判断整个程序是否处于活跃状态的变量称为标志。

标志值：

False:让程序停止运行

True:让程序继续运行

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)

输入值为“quit”时 active='quit' 程序结束。

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

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

break·continue

命令	作用
Break	跳出当前循环，不在运行循环中剩余代码
continue	跳出循环，返回循环的头部，继续运行下一次循环

current_number = 1
while current_number < 10:
    current_number += 1
#当数字是偶数时跳过本次循环使用continue，退出整个循环使用break
    if current_number % 2 == 0:
        break
        # continue
    print(current_number)

while循环处理列表与字典

for循环是一种遍历列表的有效方式，但在for循环中不应该修改列表，否则将导致Python难以跟踪其中的元素。

便历列表的同时进行修改可以使用while循环 while循环同列表字典结合使用，可收集、存储并组织大量输入，供以后查看和使用

while循环处理列表元素移动

# Start out with some users that need to be verified,
#  and an empty list to hold confirmed users.
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []

# Verify each user, until there are no more unconfirmed users.
#  Move each verified user into the list of confirmed users.
while unconfirmed_users:
    current_user = unconfirmed_users.pop()
    
    print("Verifying user: " + current_user.title())
    confirmed_users.append(current_user)
    
# Display all confirmed users.
print("
The 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

while循环删除列表中特定值

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

#! /usr/bin/env python
# -*- coding: utf-8 -*-
# Author:Jor Babe

responses = {}

# Set a flag to indicate that polling is active.
# s设置一个标志，指出调查是否继续
polling_active = True

while polling_active:
    # Prompt for the person's name and response.
    # 提示输入被调查者的名字和回答
    name = input("
What is your name? ")
    response = input("Which mountain would you like to climb someday? ")

    # Store the response in the dictionary:
    # 将调查存储在字典中
    responses[name] = response

    # Find out if anyone else is going to take the poll.
    # 是否还有继续参加调查者
    repeat = input("Would you like to let another person respond? (yes/ no) ")
    if repeat == 'no':
        polling_active = False

# Polling is complete. Show the results.
# 调查结束，显示调查结果
print("
--- Poll Results ---")
for name, response in responses.items():
    print(" %s would like to climb %s ."%(name,response))