面向对象编程是最有效的软件编写方法之一。在面向对象编程中，你编写表示现实世界中的事物和情景的类，并基于这些类来创建对象。编写类时，你定义一大类对象都有的通用行为。基于类创建对象时，每个对象都自动具备这种通用行为，然后可根据需要赋予每个对象独特的个性。使用面向对象编程可模拟现实情景，其逼真程度达到了令你惊讶的地步。

一、创建和使用类

1.创建Dog类

根据Dog 类创建的每个实例都将存储名字和年龄。我们赋予了每条小狗蹲下（sit() ）和打滚（roll_over() ）的能力：

class Dog():

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def sit(self):
        print(self.name.title()+" is now sitting.")

    def roll_over(self):
        print(self.name.title()+" rolled over!")

根据约定，在Python中，首字母大写的名称指的是类。这个类定义中的括号是空的，因为我们要从空白创建这个类。

方法_init_()

类中的函数称为方法。其中_init_()是一个特殊的方法，每当你根据Dog类创建新实例时，python都会自动运行它。在这个方法中，开头和结尾都有一条下划线以避免冲突。

方法_init_()中的形参self必不可少，且必须位于首位。当Python调用这个_init_()方法来创建Dog实例时，将自动传入实参self。每个与类相关联的方法调用都自动传递实参self，它是一个指向实例本身的引用，让实例能够访问类中的属性和方法。我们创建Dog实例时，python将调用Dog类的方法_init_()。我们将通过实参向Dog()传递名字和年龄；self会自动传递，因此我们不需要传递它。每当我们根据Dog创建实例时，都只需给最后两个形参（age和name）提供值。

self.name和self.age两个变量都有前缀self，以self为前缀的变量可供类中的所有方法使用，我们还可以通过类的任何实例来访问这些变量。通过语句 self.name = name 获取存储在形参name中的值，并将其存储到变量name中，然后该变量被关联到当前创建的实例。像这样可通过实例访问的变量称为属性。

2.根据类创建实例

class Dog():
	.....
	.....

my_dog = Dog('milk',3)

print("My dog's name is "+my_dog.name.title()+".")
print("My dog is "+str(my_dog.age)+" years old.")
my_dog.roll_over()

输出如下：

My dog's name is Milk.
My dog is 3 years old.
Milk rolled over!

可通过句点运算符访问属性、调用方法。

动手试一试9-1 — 9-3

#9-1

print("\n9-1:\n")

class Restaurant():

    def __init__(self,restaurant_name,cuisine_type):
        self.restaurant_name = restaurant_name
        self.cuisine_type = cuisine_type

    def describe_restaurant(self):
        print(self.restaurant_name)
        print(self.cuisine_type)

    def open_restaurant(self):
        print("The "+self.cuisine_type+" restaurant named "+self.restaurant_name+" is open.")

hanhan_restaurant = Restaurant('hanhan', 'Chinese food')
hanhan_restaurant.describe_restaurant()
hanhan_restaurant.open_restaurant()

#9-2

print("\n9-2:\n")
a_restaurant = Restaurant('a','Chinese food')
a_restaurant.describe_restaurant()
a_restaurant.open_restaurant()


#9-3

print("\n9-3:\n")

class User():
    def __init__(self,first_name,last_name,sex):
        self.first_name = first_name
        self.last_name = last_name
        self.sex = sex

    def describe_user(self):
        print("first name:"+self.first_name)
        print("last_name:"+self.last_name)
        print("sex:"+self.sex)

    def greet_user(self):
        print("Hello,"+self.last_name.title()+" "+self.first_name.title()+"!")

a_user = User('goudan','li','man')
a_user.describe_user()
a_user.greet_user()

输出如下：

9-1:

hanhan
Chinese food
The Chinese food restaurant named hanhan is open.

9-2:

a
Chinese food
The Chinese food restaurant named a is open.

9-3:

first name:goudan
last_name:li
sex:man
Hello,Li Goudan!

二、使用类和属性

与函数部分类似，不再赘述。

动手试一试9-4 — 9-5

#9-4

print("\n9-4:\n")

class Restaurant():

    def __init__(self,restaurant_name,cuisine_type):
        self.restaurant_name = restaurant_name
        self.cuisine_type = cuisine_type
        self.number = 0

    def describe_restaurant(self):
        print(self.restaurant_name)
        print(self.cuisine_type)

    def open_restaurant(self):
        print("The "+self.cuisine_type+" restaurant named "+self.restaurant_name+" is open.")

    def number_served(self):
        print("This restaurant has "+str(self.number)+" people.")

    def set_number_served(self, number):
        self.number = number

    def increase_number_served(self,num):
        self.number += num


hanhan_restaurant = Restaurant('hanhan', 'Chinese food')
hanhan_restaurant.number_served()
hanhan_restaurant.number = 5
hanhan_restaurant.number_served()

hanhan_restaurant.set_number_served(10)
hanhan_restaurant.number_served()

hanhan_restaurant.increase_number_served(5)
hanhan_restaurant.number_served()


#9-5

print("\n9-5:\n")

class User():
    def __init__(self,first_name,last_name,sex):
        self.first_name = first_name
        self.last_name = last_name
        self.sex = sex
        self.login_attempts = 0

    def describe_user(self):
        print("first name:"+self.first_name)
        print("last_name:"+self.last_name)
        print("sex:"+self.sex)

    def greet_user(self):
        print("Hello,"+self.last_name.title()+" "+self.first_name.title()+"!")

    def increment_login_attempts(self):
        self.login_attempts += 1

    def reset_login_attempts(self):
        self.login_attempts = 0

a_user = User('goudan','li','man')
print(a_user.login_attempts)
a_user.increment_login_attempts()
a_user.increment_login_attempts()
print(a_user.login_attempts)
a_user.reset_login_attempts()
print(a_user.login_attempts)

输出如下：

9-4:

This restaurant has 0 people.
This restaurant has 5 people.
This restaurant has 10 people.
This restaurant has 15 people.

9-5:

0
2
0

三、继承

编写类时，并非总是要从空白开始。如果你要编写的类是另一个现成类的特殊版本，可使用继承。一个类继承另一个类时，它将自动获得另一个类的所有属性和方法；原有的类称为父类，而新类称为子类。子类继承了其父类的所有属性和方法，同时还可以定义自己的属性和方法。

1.子类的方法_init_()

class Car():

    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def get_descriptive_name(self):
        long_name = str(self.year)+' '+self.make+' '+self.model
        return  long_name.title()

    def read_odometer(self):
        print("This car has "+str(self.odometer_reading)+" mlies on it.")

    def update_odometer(self,mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You can't roll back an odometer!")

    def increment_odometer(self,miles):
        self.odometer_reading += miles


class ElectricCar(Car):

    def __init__(self,make,model,year):
        super().__init__(make,model,year)

my_telsa = ElectricCar('telsa','model s',2016)
print(my_telsa.get_descriptive_name())

上述代码创建了一个新类电动汽车，继承了类汽车的内容.

super() 是一个特殊函数，帮助Python将父类和子类关联起来。这行代码让Python调用ElectricCar 的父类的方法__init__() ，让ElectricCar 实例包含父类的所有属性。父类也称为超类（superclass），名称super因此而得名。

2.添加特有属性

class Car():
xxx

class ElectricCar(Car):

    def __init__(self,make,model,year):
        super().__init__(make,model,year)
        self.battery_size = 70

    def describe_battery(self):
        print("This car has a "+str(self.battery_size)+" -kWh battery.")

my_telsa = ElectricCar('telsa','model s',2016)
print(my_telsa.get_descriptive_name())
my_telsa.describe_battery()

3.重写父类的方法

只需在子类中定义一个方法，与想要修改的父类方法名称一致即可。

4.将实例用作属性

与继承类似。

class Car():
xxx

class Battery():

    def __init__(self,battery_size=70):
        self.battery_size =battery_size

    def describe_battery(self):
        print("This car has a "+str(self.battery_size)+" -kWh battery.")

class ElectricCar(Car):

    def __init__(self,make,model,year):
        super().__init__(make,model,year)
        self.battery = Battery()

my_telsa = ElectricCar('telsa','model s',2016)

print(my_telsa.get_descriptive_name())
my_telsa.battery.describe_battery()

动手试一试 9-6 — 9-9


# 9-6

print("\n9-6:\n")

class Restaurant():

    def __init__(self,restaurant_name,cuisine_type):
        self.restaurant_name = restaurant_name
        self.cuisine_type = cuisine_type

    def describe_restaurant(self):
        print(self.restaurant_name)
        print(self.cuisine_type)

    def open_restaurant(self):
        print("The "+self.cuisine_type+" restaurant named "+self.restaurant_name+" is open.")


class IceCreamStand(Restaurant):

    def __init__(self,restaurant_name,cuisine_type):
        super().__init__(restaurant_name,cuisine_type)
        self.restaurant_name = restaurant_name
        self.cuisine_type = cuisine_type

    def describe_icecream(self):
        flavours = ['milk','chocolate','sugar']
        print("We have the following tastes:\n"+str(flavours))

ice = IceCreamStand('hanhan','Chinese')
ice.open_restaurant()
ice.describe_icecream()


# 9-7
print("\n9-7:\n")

class User():
    def __init__(self,first_name,last_name,sex):
        self.first_name = first_name
        self.last_name = last_name
        self.sex = sex
        self.login_attempts = 0

    def describe_user(self):
        print("first name:"+self.first_name)
        print("last_name:"+self.last_name)
        print("sex:"+self.sex)

    def greet_user(self):
        print("Hello,"+self.last_name.title()+" "+self.first_name.title()+"!")

    def increment_login_attempts(self):
        self.login_attempts += 1

    def reset_login_attempts(self):
        self.login_attempts = 0

class Admin(User):

    def __init__(self,first_name,last_name,sex):
        super().__init__(first_name,last_name,sex)
        self.first_name = first_name
        self.last_name = last_name

    def show_privileges(self):
        string = ["can add post","can delete post","can ban user"]
        print("User's power:\n"+str(string))

goudan = Admin('goudan','li','man')
goudan.show_privileges()


#9-8

print("\n9-8:\n")

class Privileges():

    def __init__(self,list=["can add post","can delete post","can ban user"]):
        self.list = list

    def show_privileges(self):
        print(self.list)

class Admin(User):

    def __init__(self,first_name,last_name,sex):
        super().__init__(first_name,last_name,sex)
        self.first_name = first_name
        self.last_name = last_name
        self.privilege = Privileges()

goudandan = Admin('goudandan','li','man')
goudandan.privilege.show_privileges()


#9-9

print("\n9-9:\n")

class Car():

    def __init__(self,make,model,year):
        self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 0

    def get_descriptive_name(self):
        long_name = str(self.year)+' '+self.make+' '+self.model
        return  long_name.title()

    def read_odometer(self):
        print("This car has "+str(self.odometer_reading)+" mlies on it.")

    def update_odometer(self,mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You can't roll back an odometer!")

    def increment_odometer(self,miles):
        self.odometer_reading += miles

class Battery():

    def __init__(self,battery_size=70):
        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
        else:
            self.battery_size = self.battery_size

class ElectricCar(Car):

    def __init__(self,make,model,year):
        super().__init__(make,model,year)
        self.battery = Battery()



xiaoniao = ElectricCar('telsa','model s',2016)
print(xiaoniao.get_descriptive_name())
xiaoniao.battery.describe_battery()
xiaoniao.battery.get_range()
xiaoniao.battery.upgrade_battery()
xiaoniao.battery.describe_battery()
xiaoniao.battery.get_range()

输出如下：

9-6:

The Chinese restaurant named hanhan is open.
We have the following tastes:
['milk', 'chocolate', 'sugar']

9-7:

User's power:
['can add post', 'can delete post', 'can ban user']

9-8:

['can add post', 'can delete post', 'can ban user']

9-9:

2016 Telsa Model S
This car has a 70 -kWh battery.
This car can go approximately 240 miles on a full charge.
This car has a 85 -kWh battery.
This car can go approximately 270 miles on a full charge.

四、导入类

同函数。

动手试一试 9-10 — 9-12

略

五、python标准库

1.collections模块中的类——OrderedDict

字典让你能够将信息关联起来，但它们不记录你添加键—值对的顺序。要创建字典并记录其中的键—值对的添加顺序，可使用模块collections 中的OrderedDict 类。OrderedDict 实例的行为几乎与字典相同，区别只在于记录了键—值对的添加顺序。

from collections import OrderedDict

favourite_languages = OrderedDict()

favourite_languages['jen'] = 'python'
favourite_languages['tom'] = 'java'

for name,language in favourite_languages.items():
    print(name)
    print(language)

输出如下：

jen
python
tom
java

动手试一试9-13 9-14

9-13 略

#9-14

print("\n9-14:\n")

from random import randint

class Die():

    def __init__(self,sides=6):
        self.sides = sides

    def roll_die(self):
        print(randint(1,self.sides))

dice_6 = Die()
dice_10 = Die(10)
dice_20 = Die(20)

print("The dice which has 6 sides:")
for i in range(10):
    dice_6.roll_die()

print("\nThe dice which has 10 sides:")
for i in range(10):
    dice_10.roll_die()

print("\nThe dice which has 20 sides:")
for i in range(10):
    dice_20.roll_die()

输出如下：

9-14:

The dice which has 6 sides:
3
3
5
5
3
1
5
6
3
1

The dice which has 10 sides:
2
7
8
6
2
10
7
2
8
1

The dice which has 20 sides:
17
16
12
4
13
12
8
4
17
6

Landing guy_964

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Python编程：从入门到实践------第9章：类

一、创建和使用类

1.创建Dog类

方法_init_()

2.根据类创建实例

二、使用类和属性

三、继承

1.子类的方法_init_()

2.添加特有属性

3.重写父类的方法

4.将实例用作属性

四、导入类

五、python标准库

1.collections模块中的类——OrderedDict

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