【Hello Python World】Week 5(1)：类

9-1 餐馆

9-2 三家餐馆

9-3 用户

9-4 就餐人数

9-5 尝试登录次数

9-6 冰淇淋小店

9-7 管理员

9-8 权限

9-9 电瓶升级

9-10 导入Restaurant类

9-11 导入Admin类

9-12 多个模块

9-13 使用OrderedDict

9-14 骰子

9-15 Python Module of the Week

本章介绍的内容是类，虽然书中篇幅不大，不过是重点章节之一。

9-1 餐馆

创建一个名为

Restaurant

的类，其方法

__init__()

设置两个属性：

restaurant_name

和

cuisine_type

。创建一个名为

describe_restaurant()

的方法和一个名为

open_restaurant()

的方法，其中前者打印前述两项信息，而后者打印一条消息，指出餐馆正在营业。

根据这个类创建一个名为

restaurant

的实例，分别打印其两个属性，再调用前述两个方法。

class Restaurant:
def __init__(self, n, t):
self.restaurant_name = n
self.cuisine_type = t

def describe_restaurant(self):
print("The restaurant is called " + self.restaurant_name + " and the cuisine type is " + self.cuisine_type)
def open_restaurant(self):
print("We are ready for service!")

restaurant = Restaurant("JP", "Chinese")
restaurant.describe_restaurant()
restaurant.open_restaurant()

#输出
# The restaurant is called JP and the cuisine type is Chinese
# We are ready for service!

注意：类要紧跟

self

！

9-2 三家餐馆

根据你为完成练习

9-1

而编写的类创建三个实例，并对每个实例调用方法

describe_restaurant()

。

class Restaurant:
def __init__(self, n, t):
self.restaurant_name = n
self.cuisine_type = t

def describe_restaurant(self):
print("The restaurant is called " + self.restaurant_name + " and the cuisine type is " + self.cuisine_type)
def open_restaurant(self):
print("We are ready for service!")

restaurant1 = Restaurant("JP", "Chinese")
restaurant2 = Restaurant("JJ", "Guangdong")
restaurant3 = Restaurant("PP", "Chaoshan")
restaurant1.describe_restaurant()
restaurant2.describe_restaurant()
restaurant3.describe_restaurant()

#输出
#The restaurant is called JP and the cuisine type is Chinese
#The restaurant is called JJ and the cuisine type is Guangdong
#The restaurant is called PP and the cuisine type is Chaoshan

9-3 用户

创建一个名为

User

的类，其中包含属性

first_name

和

last_name

，还有用户简介通常会存储的其他几个属性。在类

User

中定义一个名 为

describe_user()

的方法，它打印用户信息摘要；再定义一个名为

greet_user()

的方法，它向用户发出个性化的问候。

创建多个表示不同用户的实例，并对每个实例都调用上述两个方法。

class User:
def __init__(self, fn, ln):
self.first_name = fn
self.last_name = ln
def describe_user(self):
print("The user's name is " + self.first_name + ' ' + self.last_name)
def greet_user(self):
print("Hello! " + self.first_name + ' ' + self.last_name)

jp1 = User("JP", "Wang")
jp2 = User("JJ", "W")
jp3 = User("PP", 'w')

jp1.greet_user()
jp2.greet_user()
jp3.greet_user()

#输出
#Hello! JP Wang
#Hello! JJ W
#Hello! PP w

9-4 就餐人数

在为完成练习

9-1

而编写的程序中，添加一个名为

number_served

的属性，并将其默认值设置为

0

。根据这个类创建一个名为

restaurant

的实例；打印有多少人在这家餐馆就餐过，然后修改这个值并再次打印它。

添加一个名为

set_number_served()

的方法，它让你能够设置就餐人数。调用这个方法并向它传递一个值，然后再次打印这个值。 添加一个名为

increment_number_served()

的方法，它让你能够将就餐人数递增。调用这个方法并向它传递一个这样的值：你认为这家餐馆每天可能接待的就餐人数。

class Restaurant:
def __init__(self, n, t, ns):
self.restaurant_name = n
self.cuisine_type = t
self.number_served = ns

def describe_restaurant(self):
print("The restaurant is called " + self.restaurant_name + " and the cuisine type is " + self.cuisine_type + ", and there had been " + str(self.number_served) + " people been to here!")
def open_restaurant(self):
print("We are ready for service!")

restaurant = Restaurant("JP", "Chinese", 10)
restaurant.describe_restaurant()
restaurant.number_served = 5
restaurant.describe_restaurant()
#输出
#The restaurant is called JP and the cuisine type is Chinese, and there had been 10 people been to here!
#The restaurant is called JP and the cuisine type is Chinese, and there had been 5 people been to here!

9-5 尝试登录次数

在为完成练习

9-3

而编写的

User

类中，添加一个名为

login_attempts

的属性。编写一个名为

increment_login_attempts()

的方法， 它将属性

login_attempts

的值加

1

。再编写一个名为

reset_login_attempts()

的方法，它将属性

login_attempts

的值重置为

0

。 根据

User

类创建一个实例，再调用方法

increment_login_attempts()

多次。打印属性

login_attempts

的值，确认它被正确地递增；然后，调用方法

reset_login_attempts()

，并再次打印属性

login_attempts

的值，确认它被重置为

0

。

class User:
def __init__(self, fn, ln):
self.first_name = fn
self.last_name = ln
self.login_attempts = 0
def describe_user(self):
print("The user's name is " + self.first_name + ' ' + self.last_name)
def greet_user(self):
print("Hello! " + self.first_name + ' ' + self.last_name)
def increment_login_attempts(self):
self.login_attempts += 1
def reset_login_attempts(self):
self.login_attempts = 0

jp = User("JP", "Wang")
print(jp.login_attempts)
jp.increment_login_attempts()
print(jp.login_attempts)
jp.increment_login_attempts()
print(jp.login_attempts)
jp.reset_login_attempts()
print(jp.login_attempts)
#输出
#0
#1
#2
#0

9-6 冰淇淋小店

冰淇淋小店是一种特殊的餐馆。编写一个名为

IceCreamStand

的类，让它继承你为完成练习

9-1

或练习

9-4

而编写的

Restaurant

类。这两个版本的

Restaurant

类都可以，挑选你更喜欢的那个即可。添加一个名为

flavors

的属性，用于存储一个由各种口味的冰淇淋组成的列表。编写一个显示这些冰淇淋的方法。创建一个

IceCreamStand

实例，并调用这个方法。

class Restaurant:
def __init__(self, n, t, ns):
self.restaurant_name = n
self.cuisine_type = t
self.number_served = ns

def describe_restaurant(self):
print("The restaurant is called " + self.restaurant_name + " and the cuisine type is " + self.cuisine_type + ", and there had been " + str(self.number_served) + " people been to here!")
def open_restaurant(self):
print("We are ready for service!")

class IceCreamStand(Restaurant):
def __init__(self, n, t, ns):
super().__init__(n,t,ns)
self.flavors = ['Milk', 'Apple', 'Strawberry', 'Mango']

ics = IceCreamStand("JP", "Chinese", 10)
ics.describe_restaurant()
for flavor in ics.flavors:
print("The ice-cream stand has flavors like " + flavor)

#输出
#The restaurant is called JP and the cuisine type is Chinese, and there had been 10 #people been to here!
#The ice-cream stand has flavors like Milk
#The ice-cream stand has flavors like Apple
#The ice-cream stand has flavors like Strawberry
#The ice-cream stand has flavors like Mango

9-7 管理员

管理员是一种特殊的用户。编写一个名为

Admin

的类，让它继承你为完成练习9-3或练习9-5而编写的User 类。添加一个名为privileges 的属性，用于存储一个由字符串（如

"can add post"

、

"can delete post"

、

"can ban user"

等）组成的列表。编写一个名为

show_privileges()

的方法，它显示管理员的权限。创建一个

Admin

实例，并调用这个方法。

class User:
def __init__(self, fn, ln):
self.first_name = fn
self.last_name = ln
self.login_attempts = 0
def describe_user(self):
print("The user's name is " + self.first_name + ' ' + self.last_name)
def greet_user(self):
print("Hello! " + self.first_name + ' ' + self.last_name)
def increment_login_attempts(self):
self.login_attempts += 1
def reset_login_attempts(self):
self.login_attempts = 0

class Admin(User):
def __init__(self, fn, ln, prv):
super().__init__(fn, ln)
self.privileges = prv

def show_privileges(self):
self.describe_user()
print("The admin has privileges that " + self.privileges)

jp = Admin("JP", "Wang", "Can ban user")
jp.show_privileges()

#输出
#The user's name is JP Wang
#The admin has privileges that Can ban user

注意！

super

要加括号(一开始没加括号把我坑惨了)

还是

self

的问题

9-8 权限

编写一个名为

Privileges

的类，它只有一个属性——

privileges

，其中存储了练习

9-7

所说的字符串列表。将方法

show_privileges()

移到这个类中。在

Admin

类中，将一个

Privileges

实例用作其属性。创建一个

Admin

实例，并使用方法

show_privileges()

来显示其权限。

class User:
def __init__(self, fn, ln):
self.first_name = fn
self.last_name = ln
self.login_attempts = 0
def describe_user(self):
print("The user's name is " + self.first_name + ' ' + self.last_name)
def greet_user(self):
print("Hello! " + self.first_name + ' ' + self.last_name)
def increment_login_attempts(self):
self.login_attempts += 1
def reset_login_attempts(self):
self.login_attempts = 0

class Admin(User):
def __init__(self, fn, ln, prv):
super().__init__(fn, ln)
self.privileges = ['ban others', 'close the web', 'set someone free']

def show_privileges(self):
for privilege in self.privileges:
print("The admin has privileges that " + privilege)

jp = Admin("JP", "Wang")
jp.show_privileges()

#输出
#The admin has privileges that ban others
#The admin has privileges that close the web
#The admin has privileges that set someone free

9-9 电瓶升级

在本节最后一个

electric_car.py

版本中，给

Battery

类添加一个名为

upgrade_battery()

的方法。这个方法检查电瓶容量，如果它不是

85

，就将它设置为

85

。创建一辆电瓶容量为默认值的电动汽车，调用方法

get_range()

，然后对电瓶进行升级，并再次调用

get_range()

。你会看到这辆汽车的续航里程增加了。

class Battery:
def __init__(self, battery_size=60):
self.battery_size = battery_size
def describe_battery(self):
print("This car has a " + str(self.battery_size) + "-kWh battery.")
def get_range(self):
if self.battery_size == 70:
range = 240
elif self.battery_size == 85:
range = 270
message = "This car can go approximately " + str(range)
message += " miles on a full charge."
print(message)
def upgrade_battery(self):
if self.battery_size != 85:
self.battery_size = 85

bat = Battery(70)
bat.get_range()
bat.upgrade_battery()
bat.get_range()

#输出
#This car can go approximately 240 miles on a full charge.
#This car can go approximately 270 miles on a full charge.

9-10 导入Restaurant类

将最新的

Restaurant

类存储在一个模块中。在另一个文件中，导入

Restaurant

类，创建一个

Restaurant

实例，并调 用

Restaurant

的一个方法，以确认

import

语句正确无误。

#将Restaurant类放在mod1.py中，并且注意将mod1.py放在与主模块文件相同的目录下
#主模块如下：
from mod1 import Restaurant
restaurant = Restaurant("JP", "Chinese", 10)
restaurant.describe_restaurant()
#输出
#The restaurant is called JP and the cuisine type is Chinese, and there had been 10 people been to here!

9-11 导入Admin类

以为完成练习

9-8

而做的工作为基础，将

User

、

Privileges

和

Admin

类存储在一个模块中，再创建一个文件，在其中创建一个

Admin

实例 并对其调用方法

show_privileges()

，以确认一切都能正确地运行。

#将3个类都放在mod1.py中，并且注意将mod1.py放在与主模块文件相同的目录下，主模块代码如下：
jp = Admin("JP", "Wang")
jp.show_privileges()

#输出
#The admin has privileges that ban others
#The admin has privileges that close the web
#The admin has privileges that set someone free

9-12 多个模块

将

User

类存储在一个模块中，并将

Privileges 和Admin

类存储在另一个模块中。再创建一个文件，在其中创建一个

Admin

实例，并对其调用方法

show_privileges()

，以确认一切都依然能够正确地运行。

仍然可以正常运行，此处代码省略(作者巨无聊)

9-13 使用OrderedDict

在练习

6-4

中，你使用了一个标准字典来表示词汇表。请使用

OrderedDict

类来重写这个程序，并确认输出的顺序与你在字典中添加键—值对的顺序一致。

#原有程序
#language = {'str()':'Change other types into string', 'len()':'Get length of an array', 'del':'Delete a member in an union type', 'for':'Means loop', 'title()':'Print a string with an UPPER first char'}
#for key, value in language.items():
#     print(key + ' : ' + value)

class OrderedDict:
def __init__(self, o, d):
self.order = o
self.definition = d
def printOrder(self):
print(self.order + ':' + self.definition)

languages = (OrderedDict('str()', 'Change other types into string'), OrderedDict('len()','Get length of an array'), OrderedDict('del','Delete a member in an union type'), OrderedDict('for','Means loop'), OrderedDict('title()','Print a string with an UPPER first char'))
for language in languages:
language.printOrder()

#输出
#str():Change other types into string
#len():Get length of an array
#del:Delete a member in an union type
#for:Means loop
#title():Print a string with an UPPER first char

9-14 骰子

模块

random

包含以各种方式生成随机数的函数，其中的

randint()

返回一个位于指定范围内的整数，例如，下面的代码返回一个

1~6

内的整数：

from random import randint

x = randint(1, 6)

请创建一个

Die

类，它包含一个名为

sides

的属性，该属性的默认值为

6

。编写一个名为

roll_die()

的方法，它打印位于

1

和骰子面数之间的随机数。创建一个

6

面的骰子，再掷

10

次。 创建一个

10

面的骰子和一个

20

面的骰子，并将它们都掷

10

次。

from random import randint

class Die:
def __init__(self, s = 6):
self.side = s
def roll_die(self):
print("The result of a " + str(self.side) + " die is " + str(randint(1, self.side)))

d1 = Die()
for i in range(1,11):
d1.roll_die()
print("----------")
d2 = Die(10)
for i in range(1,11):
d2.roll_die()
print("----------")
d3 = Die(20)
for i in range(1,11):
d3.roll_die()

#输出
#The result of a 6 die is 6
#The result of a 6 die is 1
#The result of a 6 die is 2
#The result of a 6 die is 6
#The result of a 6 die is 4
#The result of a 6 die is 4
#The result of a 6 die is 3
#The result of a 6 die is 4
#The result of a 6 die is 6
#The result of a 6 die is 3
#----------
#The result of a 10 die is 9
#The result of a 10 die is 1
#The result of a 10 die is 5
#The result of a 10 die is 9
#The result of a 10 die is 2
#The result of a 10 die is 2
#The result of a 10 die is 3
#The result of a 10 die is 1
#The result of a 10 die is 5
#The result of a 10 die is 6
#----------
#The result of a 20 die is 10
#The result of a 20 die is 16
#The result of a 20 die is 18
#The result of a 20 die is 17
#The result of a 20 die is 12
#The result of a 20 die is 14
#The result of a 20 die is 7
#The result of a 20 die is 6
#The result of a 20 die is 5
#The result of a 20 die is 16

9-15 Python Module of the Week

要了解

Python

标准库，一个很不错的资源是网站

Python Module of the Week

。请访问

http://pymotw.com/

并查看其中的目录，在其中找一个你感兴趣的模块进行探索，或阅读模块

collections

和

random

的文档。

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