Beginner python notes (encapsulation, reflection, class built-in attr attributes, packaging and authorization)

Posted by melqui on Mon, 16 Mar 2020 12:53:01 +0100

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This article is still the object-oriented content, mainly analyzes the following three methods of object-oriented programming: encapsulation, reflection, dynamic import module, class built-in attr attribute, packaging and authorization


The essence of encapsulation:
Putting methods in classes and classes in modules is called loading;

In other places, when importing modules, referencing classes, and calling methods, you can't see the specific logic of the corresponding modules, classes, and methods. You only need to know the name, because they are hidden. This is called sealing

The essence of encapsulation is to distinguish the inside and the outside clearly, so encapsulation is a kind of thought, the inside is the inside, the outside is the outside

class People:
    #Variables that start with "U" are hidden variables that cannot be seen when they are used externally
    _place= 'Beijing'
    __position= 'Python'
    def __init__(self,id_num,name,age,salary):
        self.id_num= id_num name
        self.age= age
        self.salary= salary

    def get_id(self):
        print('I am a privacy,I need to find id [%s]' %self.id_num)

v1= People('12345678','Zoro',22,2000000)
#Although it is hidden, it can still be called. Hiding is just a convention, but python does not really restrict your access

#But at the beginning, you must bring the class name

Operation result:

Encapsulation in real effect: clearly distinguish the internal and external implementation logic, which cannot be known by the external, and provide an access interface for the logic encapsulated into the internal to be used by the external


The nature of reflection:
Also known as program introspection, it mainly refers to the ability of a program to access, detect and modify its own state

class BadGuy:
    feature= 'Ugly'  #Characterized by ugliness
    def __init__(self,name,address):  #Two parameters, one name and one address = name
        self.address= address

    #Actions (function properties)
    def sell_house(self):
        print('[%s] Selling house'

    def rent_house(self):
        print('[%s] Renting a house'

p1= BadGuy('Black intermediary','Shahe')


#Start self reflection
print(hasattr(p1,'name'))  #Whether there is the attribute name in the object, and the return value is Boolean
#The first parameter of the hasattr() reflection function is an object and the second is a string, which is equivalent to

#Return the value corresponding to the property name (the function property returns the function memory address),
#The first parameter is an object and the second parameter is a string. If it does not exist, an error will be reported
#The third parameter is Default, indicating that if it does not exist, the third parameter will be output
print(getattr(p1,'r_house','The property does not exist'))

setattr(p1,'The fifth emperor of the new world','Monkey D Luffy')  #Add a key value pair in the attribute dictionary, that is, one more attribute
#You can also add function properties
setattr(p1,'add_num',lambda x:x+1)  #Anonymous function of self increasing 1
setattr(p1,'join_str',lambda'yes BadGuy')  #The anonymous function of concatenated string
print(p1.add_num(1313))  #Calling function
print(p1.join_str(p1))  #Because it is an anonymous function with self, the parameter passed in is the object name

delattr(p1,'The fifth emperor of the new world')  #Delete the key value pairs in the attribute dictionary. The first parameter is the object name and the second parameter is the key

Operation result:

Dynamic import module

First, customize a simple module and put it into the web folder to form a package:

#from web import test  #Import the test custom module in the web package normally

#Dynamic import module
module = __import__('web.test')  #Import the test module in the web package under the relative path
print(module)  #In fact, only the web package is imported. The whole module represents the web without test1
#In this way, you can import test1 under the web
module.test.test1()  #Import and call test1 function

#Using the importlib module to import
import importlib
m = importlib.import_module('web.test')
print(m)  #Different from the module, the imported module is test
#So it can be called directly
m.test2()  #m.test.test2 is not needed

Operation result:

Class built in attr attribute

There are three types of built-in attr attributes:

class Test:
    y = 2020
    def __init__(self,x):
        self.x= x

    def __getattr__(self,item):  #item is a required parameter
        print('Being implemented__getattr__Method')

    def __delattr__(self,item):

    def __setattr__(self,key,value):  #When setting the value, it is added to the property dictionary, so the key value pair is passed in
        print('In use__setattr__Set value')
        #__Set value operation is required in setattr \
        self.__dict__[key]= value  #Set the original property dictionary

p1= Test(520)

#__getattr Uuuuuu method
print(p1.x)  #Using the property dictionary to get properties
print(getattr(p1,'__getattr__'))  #Using the getattr function to get properties
p1.jjjjjjjjjjjjjjjjjj  #A nonexistent property name will trigger the execution of the getattr method

#__delatrr method
del p1.y  #When del operation is executed, the execution of the "delattr" method will be triggered
#p1.__dict__.pop('x')  #This method does not trigger the execution of the

#__setattr? Method, when the set value of life will be triggered
print(p1.__dict__)  #Output original attribute dictionary
p1.y= 13  #If you set two new key value pairs, you will execute Zu setattr twice__
p1.z= 14

Operation result:

__The benefits of getattr \
When an attribute that does not exist is passed in, an error will not be reported, but a corresponding reminder will be output

class Test:
    y = 2020
    def __init__(self,x):
        self.x= x

    def __getattr__(self,item):  #item is a required parameter
        print('Properties you are looking for[%s]Non-existent!' %item)  #The item at this time is the property passed in when calling

p1= Test(520)

#__getattr Uuuuuu method
print(p1.x)  #Using the property dictionary to get properties
print(getattr(p1,'__getattr__'))  #Using the getattr function to get properties
p1.jjjjjjjjjjjjjjjjjj  #A nonexistent property name will trigger the execution of the getattr method

Operation result:

Packaging and authorization

Packaging: one type of packaging is usually used to customize the existing types. You can create, modify and delete the functions of the original products, and the others remain the same

Authorization: authorization is a feature of packaging. All updated functions are handled by some part of the new class, but the existing functions are authorized to the default properties of the object. The key point to implement authorization is to override the getattr method

import time  #Import time module

class Open:  #A class that produces a file
    def __init__(self,filename,mode,encoding):
        #self.filename= filename
        #Open a file and set it to the self.file property
        self.file= open(filename,mode,encoding=encoding)
        self.mode= mode
        self.encoding= encoding

    #A transfer station
    def __getattr__(self,item):
        print('[%s]Non-existent!' %item)
        print(item,type(item))  #Output the incoming value and its type

        #Implementation of authorization
        return getattr(self.file, item)
        #Get the information in self.file. If it does not exist, a new one will be created and the memory address of the new method will be returned

    #Overriding the getattr method, that is, customizing a write method, means that a write method already exists,
    #So it will not trigger the getattr method to create a new write method
    def write(self,line):  #The second parameter is the content of the incoming write
        t = time.strftime('%Y-%m-%d %t')  #Character format display system time, year month day
        self.file.write(t + line)  #String splicing

#Instantiation and call
p1= Open('a.txt','r+','gbk')
print(p1.file)  #Output file information  #Trigger the getattr, run the getattr() method
#After creating an item method, you can call the
print(p1.write)  #Trigger getattr again to create a new write method

#You can write
p1.write('Is ok...\n')
p1.write('Finally, it can be written in\n')

p1.file.close()  #Close files to update data

Operation result:

The contents are also written in the file normally:

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Topics: Attribute encoding Python Lambda