Python learning day21

python day21

combination

What is a combination

Refers to a combination of attributes in the object, another object is

Why use a combination of

As inheritance and object combination, in order to reduce code redundancy

# 组合的实现:
class People:
    def __init__(self, name, age, sex):
        self.name = name
        self.age = age
        self.sex = sex

class Teacher(People):
    def __init__(self, name, age, sex):
        super().__init__(name, age, sex)

class Student(People):
    def __init__(self, name, age, sex):
        super().__init__(name, age, sex)

class Date:
    def __init__(self, year, month, day):
        self.year = year
        self.month = month
        self.day = day

    def tell_birth(self):
        print(f'{self.year}年{self.month}月{self.day}日')

tea1 = Teacher('momo', 24, 'female')
date_obj = Date(2018, 8, 17)
tea1.date = date_obj
tea1.date.tell_birth()

Combination Summary

inherit:

The relationship between class and class, what kind of what is the relationship between child and parent class affiliation

combination:

The relationship between objects and object, what kind of what the relationship between an object has another object

Package

What is the package

It refers to a package stack of attributes (characteristics and skills) encapsulated into an object

Purpose is to fetch the stored data objects may be .the way to obtain properties

Why package

The purpose of the package for easier access, through the object .to obtain the attributes of attributes embodiment

How to package

Wherein: Variable ---> data attributes

Skills: function ---> method attribute

Within the class defined pile attributes (characteristics and skills)

Via the object .attribute property value =

Access restriction mechanism

What is the access restriction mechanism

Within the class definition, all in order __since the beginning of the data attributes and methods Properties will be hidden inside the python, can not let the outside "直接"inside access __at the beginning of the property

The purpose of access restriction mechanism

Private property and can not be easily accessed by external attributes, you can hide, not directly call external

advantage:

Logic important data obtained more rigorous, thereby ensuring the security of data

Interface: privacy attributes via an interface package, in doing business logic interface processing, and then returns to the caller data

the Attention : in python, does not enforce restrictions of access to property, inside the class __attribute beginning, just do a variation, if you want direct access, you can call the name of the deformed

__name = 'momo' #---> _类名__属性名

class ATM:
    def __flow(self):
        print('打印账单')
        
    def withdraw(self):
        self.__flow()
        print('访问限制!!')
        
atm = ATM()
atm.withdraw()

property

What is proprety

The method of python decorators built, mainly to the use of an internal class

Why use property

The purpose of using it, is an internal class method (method name DEF ()) becomes (DEF Method)

In object to call a method, the target .method () becomes a target .method (it looks like an ordinary data attributes)

How to use the property

class People:
    def __init__(self,name,weight,height):
        self.name = name 
        self.weight = weight
        self.height = height
        
    @property
    def bmi(self):
        return self.height/(self.weight ** 2)
    
    @property
    def get_name(self):
        return self.name

    # 改
    @get_name.setter
    def set_name(self, val):
        self.name = val

    # 删除
    @get_name.deleter
    def del_name(self):
        del self.name
    
p = People('momo',95,1.6)
print(p.bmi)

# 注意: 不能对被装饰过的方法属性修改.

Polymorphism

What is polymorphic

Polymorphism refers to the various forms of the same thing

Polymorphic object

Polymorphic also known as polymorphism, inheritance, polymorphism is the manifestation in the program

Polymorphic purpose is to allow a variety of different types of objects, in the case of the same function, still call the same name

Parent Class: defining a set of uniform standards

Subclass: follow uniform standards parent

Polymorphic ultimate goal: the preparation of standardized and unified sub-categories, in order to allow users to more easily call the same function method

class Animal:
    def speak(self):
        pass

class Cat(Animal):
    def speak(self):
        print('喵喵喵~~~~')
    
class Dog(Animal):
    def speak(self):
        print('汪汪汪~~~~')
    
class Pig(Animal):
    def speak(self):
        print('哼哼哼~~~~')
    
cat = Cat()
dog = Dog()
pig =pig()
cat.speak()
dog.speak()
pig.speak()

Abstract class

What is an abstract class

abc module abstract_class

purpose of usage

Forced subclass must follow the uniform standards of the parent class

import abc

class Animal(metaclass=abc.ABCMeta):

    @abc.abstractmethod
    def eat(self):
        pass

    @abc.abstractmethod
    def drink(self):
        pass

    @abc.abstractmethod
    def speak(self):
        pass

class Pig(Animal):

    def eat(self):
        print('猪在吃饭')
        pass

    def drink(self):
        pass
    
    def speak(self):
        print('哼哼哼~~~')

    def run(self):
        pass

pig = Pig()