An example tutorial to create a simple class

Create a simple class

Each real column created based on the Dog class will store the name and age. We gave each puppy the ability to squat (sit()) and roll (roll_over()):

 1 class Dog(): 2     """一次模拟小狗的简单尝试""" 3     def __init__(self, name, age): 4         """初始化属性name和age""" 5         self.name = name 6         self.age = age 7     def sit(self): 8         """模拟小狗被命令时蹲下""" 9         print(self.name.title() + "now is sitting.")10     def roll_over(self):11         """模拟小狗被命令时打滚"""12         print(self.name.title() + "rolled over!")13 my_dog = Dog('tom','3')14 print("my dog name is " + my_dog.name.title() )

By convention, in Python, the first letter is capitalized The name refers to the class: functions in the class are called methods

method__init__(), with 2 underscores at the beginning and end, this is a convention to avoid Python default methods A name conflict occurred with a normal method. We define the method __init__() to contain three formal parameters: self, name and age. In the definition of this method, the parameterself is essential and must be located in front of other formal parameters. Why must the formal parameter self be included in the method definition? Because when Python calls this __init__() method to create a Dog instance, the actual parameter self will be automatically passed in. Both variables self_name and self_age are prefixed with self. Variables prefixed with self are available to all methods in the class. We can also access these variables through any instance column of the class. Variables like this that are accessible through an instance are called properties.

#In python2.X, if you create a class, you need to add (object) after the brackets.

Accessing properties

Continuing with the above example, the method __init__() creates an instance representing a specific puppy and sets it with the value we provide The attributes name and age, and the method __init__() do not explicitly contain a return statement, but python automatically returns an example representing this puppy. We store this example in the variable my_dog.

class Dog():"""一次模拟小狗的简单尝试"""def __init__(self, name, age):"""初始化属性name和age"""self.name = name
        self.age = agedef sit(self):"""模拟小狗被命令时蹲下"""print(self.name.title() + " now is sitting.")def roll_over(self):"""模拟小狗被命令时打滚"""print(self.name.title() + " rolled over!")
my_dog = Dog('tom',3)print(my_dog.name)print(my_dog.age)#运行结果tom3

Call method

class Dog():"""一次模拟小狗的简单尝试"""def __init__(self, name, age):"""初始化属性name和age"""self.name = name
        self.age = agedef sit(self):"""模拟小狗被命令时蹲下"""print(self.name.title() + " now is sitting.")def roll_over(self):"""模拟小狗被命令时打滚"""print(self.name.title() + " rolled over!")
my_dog = Dog('tom',3)
my_dog.sit()
my_dog.roll_over()#运行结果Tom now is sitting.
Tom rolled over!

After creating an instance based on the Dog class, You can use period notation to call any method defined by Dog

Create multiple instances

class Dog():"""一次模拟小狗的简单尝试"""def __init__(self, name, age):"""初始化属性name和age"""self.name = name
        self.age = agedef sit(self):"""模拟小狗被命令时蹲下"""print(self.name.title() + " now is sitting.")def roll_over(self):"""模拟小狗被命令时打滚"""print(self.name.title() + " rolled over!")
my_dog = Dog('tom',3)
your_dog = Dog('Mei',2)print("My dog name is " + my_dog.name.title())print("Your dog name is " + your_dog.name.title())#运行结果My dog name is Tom
Your dog name is Mei

You can press Create any number of instances based on the class on demand.

Using classes and instances

Specify default values ​​for properties

Each property in a class must have an initial value , even if the value is 0 or an empty string, in some cases, such as when setting a default value, it is okay to specify this initial value in the method __init__(). If you do this for an attribute, there is no need to Contains formal parameters that provide initialization for it.

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_name
my_car = Car('audi', 'a4', '2017')print(my_car.model)print(my_car.get_descri_name())#运行结果a42017 a4 audi

Directly modify the value of the attribute

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_name
my_car = Car('audi', 'a4', '2017')print(my_car.get_descri_name())
my_car.year = 2016print(my_car.get_descri_name())#运行结果2017 a4 audi2016 a4 audi

Modify by method

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_namedef update(self, mile):"""更新里程值"""if mile > self.odometer_reading:
            self.odometer_reading = mileelse:print("You can't roll back an odometer")def increment_odometer(self,mile):"""增加里程"""self.odometer_reading += miledef read_odometer(self):"""打印汽车的里程"""print("This car has " + str(self.odometer_reading) + " miles on it.")
my_car = Car('audi', 'a4', '2017')
my_car.read_odometer()
my_car.odometer_reading = 10    #直接修改里程值my_car.update(200)     #通过方法修改里程my_car.read_odometer()
my_car.increment_odometer(10)
my_car.read_odometer()#运行结果This car has 100 miles on it.
This car has 200 miles on it.
This car has 210 miles on it.

Inheritance

If we want another class to inherit the attributes of another class, we can add the class in brackets after the class Name, for example:

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_namedef update(self, mile):"""更新里程值"""if mile > self.odometer_reading:
            self.odometer_reading = mileelse:print("You can't roll back an odometer")def increment_odometer(self,mile):"""增加里程"""self.odometer_reading += miledef read_odometer(self):"""打印汽车的里程"""print("This car has " + str(self.odometer_reading) + " miles on it.")class ElectricCar(Car):"""电动汽车的独特特性"""def __init__(self, make, model, year):"""初始化父类的属性"""super().__init__(make, model, year)
my_tesla = ElectricCar('tesla', 'model s', '2016')print(my_tesla.get_descri_name())#运行结果2016 model s tesla

In order to inherit the attributes of the parent class,

also needs to add a special function super() to help Python associate the parent class with the subclass.

In python2.X, the format of class supper is as follows:

supper(Eletric,self).__init__(make, model, year)

Give sub Class definition attributes and methods

After a class inherits another class, you can add new attributes and methods that distinguish the subclass and the parent class.

Use instances as attributes

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_namedef update(self, mile):"""更新里程值"""if mile > self.odometer_reading:
            self.odometer_reading = mileelse:print("You can't roll back an odometer")def increment_odometer(self,mile):"""增加里程"""self.odometer_reading += miledef read_odometer(self):"""打印汽车的里程"""print("This car has " + str(self.odometer_reading) + " miles on it.")class Battery():"""一次模拟电动汽车"""def __init__(self,battery_size=70):"""初始化电瓶的属性"""self.battery_size = battery_sizedef describe_battery(self):"""打印一条描述电瓶容量的消息"""print("This car has a " + str(self.battery_size) + "-kwh battery.")class ElectricCar(Car):"""电动汽车的独特特性"""def __init__(self, make, model, year):"""初始化父类的属性"""super().__init__(make, model, year)
        self.battery = Battery()
my_tesla = ElectricCar('tesla', 'model s', '2016')print(my_tesla.get_descri_name())
my_tesla.battery.describe_battery()#运行结果2016 model s tesla
This car has a 70-kwh battery.

Import class

Import single or multiple classes

A file car.py

class Car():"""一次模拟汽车的简单尝试"""def __init__(self, make, model, year):"""汽车的初始化"""self.make = make
        self.model = model
        self.year = year
        self.odometer_reading = 100def get_descri_name(self):"""描述汽车"""long_name = str(self.year) + ' ' + self.model + ' ' + self.makereturn long_namedef update(self, mile):"""更新里程值"""if mile > self.odometer_reading:
            self.odometer_reading = mileelse:print("You can't roll back an odometer")def increment_odometer(self,mile):"""增加里程"""self.odometer_reading += miledef read_odometer(self):"""打印汽车的里程"""print("This car has " + str(self.odometer_reading) + " miles on it.")class Battery():"""一次模拟电动汽车"""def __init__(self,battery_size=70):"""初始化电瓶的属性"""self.battery_size = battery_sizedef describe_battery(self):"""打印一条描述电瓶容量的消息"""print("This car has a " + str(self.battery_size) + "-kwh battery.")class ElectricCar(Car):"""电动汽车的独特特性"""def __init__(self, make, model, year):"""初始化父类的属性"""super().__init__(make, model, year)
        self.battery = Battery()

Create another file my_car.py and import a class

from  car import Car
my_car = Car('audi', 'a4', '2017')

Multiple classes can be stored in a module, so multiple classes can be imported at one time

from car import Car,Battery,ElectricCar
my_tesla = ElectricCar('tesla', 'model s', '2016')print(my_tesla.get_descri_name())
my_tesla.battery.describe_battery()

Import the entire module

import car     #导入整个模块的时候，需要使用句点表示法访问需要的类
my_tesla = car.ElectricCar('tesla', 'model s', '2016')print(my_tesla.battery)

Import all classes

from car import *    #导入所有的类

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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