Python第七章

Posted 2020-12-17 xdz-toptan

第 7 章 用户输入和while循环

7.1 函数input()的工作原理

message = input("Tell me something, and I will repeat it back to you: ")

print(message)

7.1.1 编写清晰的程序

name = input("Please enter your name: ")

print("Hello, " + name + "!")

prompt = "If you tell us who you are, we can personalize the message you see."

prompt += " What is your first name? "

name = input(prompt)

print(" Hello, " + name + "!")

7.1.2 使用int()来获取数值输入

age = input("How old are you? ")

print("I‘m " + str(age) + ".") # 可转化为字符串再打印输出，间接的赋值数字必须转化为字符串再输出打印，否则打印会出错

print("I‘m " + age + ".") # 输入的数字age为字符串可直接打印

age = input("How old are you? ") # 此处age为字符串，需用int()转换为数字才能跟数字比较大小

age >= 18

age = input("How old are you? ")

age = int(age)

if age >= 18:

print("Yes!")

判断一个人是否满足坐过山车的身高要求

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

height = int(height)

if height >= 36:

print(" You ‘re tall enough to ride!")

else:

print(" You‘ll be able to ride when you‘re a little older.")

7.1.3 求模运算符

a = 4 % 3
print(a)
b = 5 % 3
print(b)
c = 6 % 3
print(c)

如果一个数可被另一个数整除，余数就为0，因此求模运算符将返回0。

你可利用这一点来判断一个数是奇数还是偶数。

number = input("Enter a number, and I‘ll tell you if it‘s even or odd: ")

number = int(number)

if number % 2 == 0:

print(" The number " + str(number) + " is even.")

else:

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

如果你使用的是Python 2.7，应使用函数raw_input() 来提示用户输入。这个函数与Python 3中的input() 一样，也将输入解读为字符串。

7-1 汽车租赁

car = input("What kind of car would you like? ")

print("Let me see if I can find you a " + car.title() + ".")

7-2 餐馆订位

number = input("How many people are in your dinner party tonight? ")

number = int(number)

if number > 8:

print("I‘m sorry, you‘ll have to wait for a table.")

else:

print("Your table is ready.")

7-3 10的整数倍

number = input("Please enter a number: ")

number = int(number)

if number % 10 == 0:

print(str(number) + " is a multiple of 10.")

else:

print(str(number) + " is not a multiple of 10.")

7.2.1 使用while循环

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

7.2.2 让用户选择何时退出

prompt = " Tell me something, and I will repeat it back to you:"

prompt += " Enter ‘quit‘ to end the program."

message = ""

while message != ‘quit‘:

message = input(prompt)

print(message)

prompt = " Tell me something, and I will repeat it back to you:"

prompt += " Enter ‘quit‘ to end the program."

message = ""

while message != ‘quit‘:

message = input(prompt)

if message != ‘quit‘:

print(message)

7.2.3 使用标志

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)

7.2.4 使用break 退出循环

注意 在任何Python循环中都可使用break 语句。例如，可使 用break 语句来退出遍历列表或字典的for 循环。

prompt = " Please enter the name of a city you have visited:"

prompt += " (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() + ".")

7.2.5 在循环中使用continue

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

7.2.6 避免无限循环

x = 1
while x <= 5:
print(x)
x += 1 # 没这句程序会无限循环下去

7-4 披萨配料

prompt = " What topping would you like on your pizza?"

prompt += " Enter ‘quit‘ when you are finished: "

while True:

topping = input(prompt)

if topping != ‘quit‘:

print(" I will add " + topping + " to your pizza.")

else:

break

7-5 电影票

prompt = " How old are you? We will tell you the prize."

prompt += " Enter ‘quit‘ when you are finished. "

while True:

age = input(prompt)

if age == ‘quit‘:

break

age = int(age)

if age < 3:

print(" You get in free!")

elif age < 12:

print(" Your ticket is 10 dollars.")

else:

print(" Your ticket is 15 dollars.")

7-6 三个出口

prompt = " What topping would you like on your pizza?"

prompt += " Enter ‘quit‘ when you are finished: "

active = True

while active:

topping = input(prompt)

if topping != ‘quit‘:

print(" I will add " + topping + " to your pizza.")

else:

active = False

7.3.1 在列表之间移动元素

首先，创建一个待验证用户列表和?个?于存储已验证?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)

显示已验证的用户

print(" The following users have been confirmed:")
for confirmed_user in confirmed_users:
print(confirmed_user.title())

7.3.2 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)

7.3.3 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(" What 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 response? (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.title() + " would like to climb " + response.title() + ".")

7-8 熟食店

sandwich_orders = [‘tuna‘, ‘veggie‘, ‘grilled cheese‘, ‘turkey‘, ‘roast beef‘]
finished_sandwiches = []
for sandwich in sandwich_orders:
print(" I made your " + sandwich + " sandwich.")
finished_sandwiches.append(sandwich)
print("Here are the finished sandwiches:")
for sandwich in finished_sandwiches:
print(sandwich)

sandwich_orders = [‘tuna‘, ‘veggie‘, ‘grilled cheese‘, ‘turkey‘, ‘roast beef‘]
finished_sandwiches = []
while sandwich_orders:
current_sandwich = sandwich_orders.pop()
print("I‘m working on your " + current_sandwich + " sandwich.")
finished_sandwiches.append(current_sandwich)
print(" ")
for sandwich in finished_sandwiches:
print("I made a " + sandwich + " sandwich.")

7-9 五香烟熏牛肉（pastrami）卖完了

sandwich_orders = [‘pastrami‘, ‘tuna‘, ‘pastrami‘, ‘veggie‘, ‘grilled cheese‘, ‘pastrami‘, ‘turkey‘, ‘roast beef‘]
finished_sandwiches = []
print("I‘m sorry, we‘re all out of pastrami today.")
while sandwich_orders:
current_sandwich = sandwich_orders.pop()
if current_sandwich != ‘pastrami‘:
finished_sandwiches.append(current_sandwich)
print("I‘m working on your " + current_sandwich + " sandwich.")
print(" ")
for sandwich in finished_sandwiches:
print("I made a " + sandwich + " sandwich.")

sandwich_orders = [‘pastrami‘, ‘tuna‘, ‘pastrami‘, ‘veggie‘, ‘grilled cheese‘, ‘pastrami‘, ‘turkey‘, ‘roast beef‘]
finished_sandwiches = []
print("I‘m sorry, we‘re all out of pastrami today.")
while ‘pastrami‘ in sandwich_orders:
sandwich_orders.remove(‘pastrami‘)
print(" ")
while sandwich_orders:
current_sandwich = sandwich_orders.pop()
print("I‘m working on your " + current_sandwich + " sandwich.")
finished_sandwiches.append(current_sandwich)
print(" ")
for sandwich in finished_sandwiches:
print("I made a " + sandwich + " sandwich.")

7-10 梦想的度假胜地

responses = {}
name_prompt = " What‘s your name? "
place_prompt = "If you want to visit one place in the world, what would it be? "
continue_prompt = " Would you like to let someone else respond? (yes/no) "
while True:
name = input(name_prompt)
place = input(place_prompt)
responses[name] = place
repeat = input(continue_prompt)
if repeat != ‘yes‘:
break
print(" --- Results ---")
for name, place in responses.items():
print(name.title() + " would like to visit " + place.title() + ".")