Introduction to Python Classes

How to create a class:

class 类名:     pass

eg

class Bar:                                        # 定义一个类    def foo(self, arg):                           # self 永远是调用方法的对象，即中间人        print(self, self.name, self.age, arg)obj = Bar()                                       # 使用 Bar 类,创建一个对象 objprint(obj)obj.name = ‘klvchen‘obj.age = 28obj.foo(666)运行结果:<__main__.Bar object at 0x000001AB792D23C8><__main__.Bar object at 0x000001AB792D23C8> klvchen 28 666

Create a method

构造方法: __init__(self, arg)                 obj = 类(参数)普通方法：obj = 类(参数)                  obj.普通方法名()

Calling methods in a class

class Foo:    def bar(self):        print(‘bar‘)obj = Foo()          # 方法一，常用obj.bar()obj = Foo()          # 方法二Foo.bar(obj)运行结果：barbar

Fields in the class

The classes are divided into normal fields and static fields:
Normal field: Persisted object, execute only through object access
Static fields: persisted in the class, execution can be accessed through the object, or accessed through the class
eg

class Province:    country = ‘China‘                  # 静态字段    def __init__(self, name):        self.name = name               # 普通字段print(Province.country)运行结果:China

Three methods in the class:

1. Common method: Persisted in the class, called by the object, self is the object
2. Static method: Guaranteed to exist in class, called directly by class
3. Class method: Persisted in the class, called directly by the class, the CLS is the current class
Application Scenarios:
If the object needs to maintain some value, when performing a function, you need to use the value in the object, select普通方法
You do not need to select a value in any object静态方法
Note: The class saves only one copy in memory, which saves system memory
eg

class Foo:    def bar(self):        print(‘bar‘)    @staticmethod                     # 静态方法    def sta():        print(‘static method‘)    @staticmethod                     # 静态方法，带参数    def sta2(n):        print(n)Foo.sta()Foo.sta2(666)运行结果:static method666

class Foo:    @classmethod    def classmod(cls):             # 类方法, cls 是当前类 Foo        print(cls)        print(‘classmethod‘)Foo.classmod()运行结果:<class ‘__main__.Foo‘>classmethod

One of the three main features of object-oriented: encapsulation

eg

class Person:    def __init__(self, name, age):        self.name = name        self.age = age    def show(self):        print(‘%s %d‘ %(self.name, self.age))klvchen = Person(‘陈‘, 28)             # 生成对象时会自动执行 __init__() 方法klvchen.show()运行结果:陈 28

Two main characteristics of object-oriented: inheritance

To extract a method common to multiple classes into a parent class, the subclass inherits only the parent class without having to implement each method one at a A.

class Father:         passclass Son(Father):         pass

eg

class F:    def f1(self):        print(‘F.f1‘)    def f2(self):        print(‘F.f2‘)class S(F):    def s1(self):        print(‘S.s1‘)    def f2(self):        super(S, self).f2()      # 执行父类的 f2 方法        F.f2(self)               # 执行父类的 f2 方法obj = S()obj.f1()obj.s1()obj.f2()运行结果:F.f1S.s1F.f2F.f2

Python supports multiple inheritance with the following rules:

1. Left priority
2. One way to do the last
3. At the same root, the root is finally executed

eg

class F1:    def f(self):        print(‘F1.f‘)class F2:    def f(self):        print(‘F2.f‘)class S(F1, F2):    passobj = S()obj.f()运行结果:F1.f

Three main characteristics of object-oriented: polymorphism

Python native support polymorphism

When you add a @property, you can create an illusion that the field is exactly the same when you access the property

class Foo:    def bar(self):        print(‘bar‘)    @property    def per(self):        print(‘123‘)        return 1    @per.setter    def per(self, val):        print(val)    @per.deleter    def per(self):        print(888)obj = Foo()r = obj.per#print(r)obj.per = 666del obj.per运行结果:123

class Foo:    def f1(self):        return 123    def f2(self, val):        print(val)    def f3(self):        print(‘del‘)    per = property(fget=f1, fset=f2, fdel=f3)obj = Foo()ret = obj.perprint(ret)obj.per = 6666del obj.per运行结果:1236666del

Call the __call__ method directly after the object Plus ()

class Foo:    def __init__(self):        print(‘init‘)    def __call__(self, *args, **kwargs):        print(‘call‘)obj = Foo()obj()运行结果:initcall

__dict__ gets all the members of the object, returned as a dictionary

class Foo:    def __init__(self, name, age):        self.name = name        self.age = ageobj = Foo(‘klvchen‘, 28)d = obj.__dict__print(d)运行结果:{‘name‘: ‘klvchen‘, ‘age‘: 28}

Introduction to Python Classes