Inheritance and polymorphism in Python

Inherited

The way that inheritance behaves:

class Animal ():     Pass class Cat (Animal):  #Animal is the cat's parent class, or it can be said to be the base class    passprint(cat.  __bases__)# View all the cat's parent classes

Single inheritance

A class has only one parent class

Dogs and birds are animals, both have the ability to eat and drink, but swimming is a dog's special skills, flying birds ' special skills, can only be extended in this class

How a unique method in a subclass implements

Implements a unique method in a subclass that has a unique attribute for that subclass? I had a little teddy, and I gave him a name, but the bird didn't have this property.

classAnimal ():def __init__(self,kind): Self.kind=KinddefEat (self):Print('Eat ...')    defDrink (self):Print('Drink ...')classDog (Animal):def __init__(self,kind,name):#animal.__init__ (self,kind) #为继承的父类中的属性初始化赋值Super ().__init__(kind)#using Super to find the parent class has the same effect as the sentence.Self.name = Name#Initializes an assignment for properties unique to this class, derived properties    defSwimming (self):Print('Dog Swimming')classBird (Animal):defFly (self):Print('Bird Flying')    defEat (self):Print('Bird Eat') B1= Bird ('Sparrow') B2= Dog ('Tiddy','Judy')Print(B1.kind)Print(B2.name)

how a unique property in a subclass is implementedMultiple inheritance

A class has more than one parent class

classA ():defFun (self):Print('AAA')classB ():defFun (self):Print('BBB')classC ():defFun (self):Print('CCC')classD (A,B,C):#Inherit A,b,c    PassD=D () d.fun ()#AAA---> Call the Fun method in Class A, according to the inheritance order a

Simple Multiple InheritanceDiamond Inheritance

‘‘‘
    A
B       C

D       E
    F
F Inheritance de,d inheritance B,e inheritance C,BC a
The order is: F->d->b->e->c->a
‘‘‘

#another question, about Super,super really looking for the parent class? #class A ():#def Fun (self):#print (' a ')#class B (A):#def Fun (self):#super (). Fun () #--> find C#print (' B ')#class C (A):#def Fun (self):#super (). Fun () #--> find a#print (' C ')#class D (b,c): #继承B, C#def Fun (self):#super (). Fun () #--> looking for b#print (' d ')#d = d ()#D.fun () #打印结果是 a C b d##以菱形多继承为例, the discovery is based on the priority algorithm found in the upper level

Super Questioninterface classes and abstract classes

There is no interface concept in Python, and interface classes and abstract classes are concepts in Java that are designed to develop a specification

Neither the interface class nor the abstract class can be instantiated

# Interface Class #      support multiple inheritance, all methods in the interface class cannot be implemented #  abstract class #      does not support multiple inheritance, methods in abstract classes can be implemented

Interface class

 from Import Abstractmethod,abcmeta # creating a canonical class class Payment (Metaclass=abcmeta):# Specifies the meta-class     @abstractmethod    def Pay (self): Pass  # classes that inherit from this class must implement this method

Multiple inheritance of interface classes

Thinking:

How to define three classes with no duplication of code: 1. The bird-------will fly, will go 2. The dog----can swim, walk 3. Ducks---can swim, fly, walk.

 fromAbcImportAbstractmethod,abcmetaclassFly_animal (metaclass=Abcmeta): @abstractmethoddefFly (self):PassclassWalk_animal (metaclass=Abcmeta): @abstractmethoddefWalk (self):PassclassSwim_animal (metaclass=Abcmeta): @abstractmethoddefSwim (self):PassclassBird (Fly_animal,walk_animal):PassclassDog (Walk_animal,swim_animal):PassclassDuck (Walk_animal,swim_animal,fly_animal):Passb= Bird ()#error Typeerror:can ' t instantiate abstract class Bird with abstract methods fly, walk#the class that inherits the canonical interface class must implement the method of adding @abstractmethod adorner, otherwise the error

multiple inheritance of interface classesAbstract class

Rules only use single inheritance

Implement an abstract class

Import  ABC# creates a canonical class  Payment (metaclass=abc. Abcmeta):# Specifies the meta     -Class @abc    . Abstractmethoddef Pay (self):pass  # classes that inherit this class must implement this method

Polymorphic

Python natively supports polymorphism

Duck type

Inheritance and polymorphism in Python