python3学习笔记8--用户输入和while循环

• 函数 input() 的工作原理

函数input() 让程序暂停运行，等待用户输入一些文本。获取用户输入后，Python将其存储在一个变量中，以方便你使用。

函数input() 接收一个参数，即要向用户显示的提示或说明，让用户如何操作。

1、编写清晰的程序

name = input("please enter you name: ")
print("Hello," + name + "!")

2、使用int() 来获取数值输入

height = input("How tall are you ,in inchaes ? ")
height = int(height)

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

3、求模运算符

求模运算符 （%）是一个很有用的工具，它将两个数相除并返回余数：

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 number " + str(number) + " is odd.")

• while 循环简介

for 循环用于针对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。

1、使用while循环

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

2、让用户选择何时退出

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)

3、使用标志

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。

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':
        active = False
    else:
        print(message)

4、使用break 退出循环

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() + "!")

5、在循环中使用continue

current_number = 0
while current_number <=5:

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

6、避免无限循环

• 使用while 循环来处理列表和字典

1、在列表中移动元素

# 首先，创建一个待验证用户列表
# 和一个用于存储已验证用户的空列表
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []
# 验证每个用户，直到没有未验证用户为止
# 将每个经过验证的列表都移到已验证用户列表中
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())

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)

3、使用用户输入来填充字典

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 + ".")