Python 學習筆記13 類 - 繼承

時間 2019-12-09

原文原文鏈接

咱們在編程的過程當中，並不是都是要重頭開始。好比其餘人已經有現成的類，咱們可使用其餘找人編寫的類。術語稱之爲：繼承。編程

當一個類繼承例外一個類時，它能夠得到這個類的全部屬性和方法：原有的類稱之爲父類，新的類稱之爲子類。子類能夠繼承父類的全部方法和屬性，還能夠自定一些本身的方法和屬性。dom

好比咱們已經有了一個叫汽車的父類，咱們能夠繼承這個類，生成一個電動車的子類：spa

#-*- coding:utf-8 -*-

class Car():

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

    def get_description_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) + " miles on it.")

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You cannot do that.")

    def increase_odometer(self, miles):
        if miles >= 0:
            self.odometer_reading += miles
        else:
            print("The value is invalid, please input the number which should more than zero.")

'''繼承car，生成一個新類'''
class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)



my_BYD = ElectricCar("BYD", "Tang", 2019)
print(my_BYD.get_description_name())


'''
輸出:
2019 Byd Tang
'''

經過上面的代碼，咱們看到，咱們基於一個car的父類，生成了一個ElectricCar的子類。code

在類定義是，在括號裏面包含父類的名稱，來表示繼承這個類： class NewClass（SupperClass）。對象

而真正繼承父類的方法和屬性的，則是在__init__方法中的super（）方法的使用，該方法告訴Python使用父類的__init__方法，來從新構造一個類。blog

經過上面的例子，咱們能夠看到，子類能夠正確的調用父類的方法，實際上這時已是子類的方法了。繼承

咱們也能夠根據累的特性，給子類定義本身特有的屬性和方法：ip

好比電動車有一個電瓶，而且有方法能夠實時的顯示當前的電量。utf-8

#-*- coding:utf-8 -*-

class Car():

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

    def get_description_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) + " miles on it.")

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You cannot do that.")

    def increase_odometer(self, miles):
        if miles >= 0:
            self.odometer_reading += miles
        else:
            print("The value is invalid, please input the number which should more than zero.")

'''繼承car，生成一個新類'''
class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery_size = 100

    def describe_battery(self):
        print("Catr has " + str(self.battery_size) + "-kwh battery. " )



my_BYD = ElectricCar("BYD", "Tang", 2019)
print(my_BYD.get_description_name())
my_BYD.describe_battery()


'''
輸出:
2019 Byd Tang
Catr has 100-kwh battery. 
'''

在上述代碼中，咱們能夠看到，咱們在__init__方法中，添加了一個電瓶容量的屬性，get

self.battery_size = 100

而且添加了一個電動車特有的顯示電量的方法。

    def describe_battery(self):
        print("Catr has " + str(self.battery_size) + "-kwh battery. " )

這些方法是屬於子類（ElectricCar）的，它可以正確的被運行。

當父類中的某些方法，並不適用子類的時候怎麼辦吶？咱們能夠在子類中從新定義該方法。

好比Car類中有加汽油的方法，而這對電動車並不適用，咱們能夠在子類中對這個方法進行覆蓋重寫。子類在調用這個方法時，將採用子類的定義：

#-*- coding:utf-8 -*-

class Car():

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

    def get_description_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) + " miles on it.")

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You cannot do that.")

    def increase_odometer(self, miles):
        if miles >= 0:
            self.odometer_reading += miles
        else:
            print("The value is invalid, please input the number which should more than zero.")

    def fill_gas(self):
        print("Car is filling gas.")

'''繼承car，生成一個新類'''
class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery_size = 100

    def describe_battery(self):
        print("Catr has " + str(self.battery_size) + "-kwh battery. " )

    def fill_gas(self):
        print("Electric car no gas tank.")



my_BYD = ElectricCar("BYD", "Tang", 2019)
my_BYD.fill_gas()


'''
輸出:
Electric car no gas tank.
'''

咱們在編寫代碼時候，須要靈活的對類進行定義。在編程思想中，現實生活中的全部對象，均可以被定義成類。

咱們儘量多訂一些類，以簡化咱們的代碼長度，同時也變成程序代碼的維護和修改。

好比在上述例子中，咱們對電動車類增長了一個電池的屬性和相關的方法。其實咱們也能夠新建一個電池的類，將電池特有的屬性和方法獨立開來。這樣咱們能夠根據這個類生成各式各樣的實例：

#-*- coding:utf-8 -*-

class Car():

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

    def get_description_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) + " miles on it.")

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You cannot do that.")

    def increase_odometer(self, miles):
        if miles >= 0:
            self.odometer_reading += miles
        else:
            print("The value is invalid, please input the number which should more than zero.")

    def fill_gas(self):
        print("Car is filling gas.")


'''生成一個電池類'''
class Battery():
    def __init__(self, size = 100):
        self.size = size

    def describe_battery(self):
        print("Battery has " + str(self.size) + "-kwh battery. " )

'''繼承car，生成一個新類'''
class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery = Battery()

    def fill_gas(self):
        print("Electric car no gas tank.")



my_BYD = ElectricCar("BYD", "Tang", 2019)
my_BYD.battery.describe_battery()


'''
輸出:
Battery has 100-kwh battery. 
'''

我麼能夠看到咱們增長了一個電池類Battery()，該類有本身屬性 size和方法describe_battery。咱們在定義電動車時，增長了一個battery的屬性，這個屬性是一個baterry的實例，咱們能夠認爲該屬性其實是一個對象 object，咱們能夠操做和使用它的屬性和方法。

這樣作的好處就是，有關電池的屬性和方法的修改，能夠放在battery類中進行處理。EelctricCar類中，只關注與其相關的屬性和方法。好比咱們能夠添加一個電池能跑多少里程的方法，該方法與電池的容量相關：

#-*- coding:utf-8 -*-

class Car():

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

    def get_description_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) + " miles on it.")

    def update_odometer(self, mileage):
        if mileage >= self.odometer_reading:
            self.odometer_reading = mileage
        else:
            print("You cannot do that.")

    def increase_odometer(self, miles):
        if miles >= 0:
            self.odometer_reading += miles
        else:
            print("The value is invalid, please input the number which should more than zero.")

    def fill_gas(self):
        print("Car is filling gas.")


'''生成一個電池類'''
class Battery():
    def __init__(self, size = 100):
        self.size = size

    def describe_battery(self):
        print("Battery has " + str(self.size) + "-kwh battery. " )

    def show_range(self):
        print("Battery has " + str(self.size * 3) + " killmaters on full charge")

'''繼承car，生成一個新類'''
class ElectricCar(Car):
    def __init__(self, make, model, year):
        super().__init__(make, model, year)
        self.battery = Battery()

    def fill_gas(self):
        print("Electric car no gas tank.")



my_BYD = ElectricCar("BYD", "Tang", 2019)

my_BYD.battery.describe_battery()
my_BYD.battery.show_range()
my_BYD.battery.size = 200
my_BYD.battery.describe_battery()
my_BYD.battery.show_range()
'''
輸出:
Battery has 100-kwh battery. 
Battery has 300 killmaters on full charge
Battery has 200-kwh battery. 
Battery has 600 killmaters on full charge
'''