【Hello Python World】Week 5(1)：类

其他 2018-09-04 23:32:13 阅读次数: 0

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。 

本题没有代码，上相关网站浏览文档即可

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