Shulou(Shulou.com)05/31 Report--

This article focuses on "Python built-in properties getattribute interceptor how to use", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to use the Python built-in attribute getattribute interceptor.

Introduction

Because all classes in python inherit the object class by default.

The object class provides many original built-in properties and methods, so user-defined classes inherit these built-in properties in Python.

You can use the dir () function to see that although python provides a lot of built-in properties, not many are commonly used in actual development. However, the built-in properties provided by many systems need to be rewritten before they are used in actual development.

For python, an attribute or function can be understood as an attribute

1. The use of the built-in attribute _ _ getattribute__ 1. Override the _ _ getattribute__ method class Student (object): country = "china" # def _ init__ (self,name,age): self.name = name self.age = age def _ getattribute__ (self, attr): # Note: attr is the passed property name Not the attribute value print ("start the property verification intercept function") print (attr) return object.__getattribute__ (self, attr) # returns the attribute name S1 = Student ("tom", 19) print (Student.country,s1.country,s1.name,s1.age) # invokes the attribute The _ _ getattribute__ method''is called to notice the result. The property is called four times, but the _ _ getattribute__ method is called only three times. Start attribute check intercept function country start attribute check intercept function name start attribute check intercept function agechina china tom 19 check interceptor

Analysis and summary:

1. Attribute _ attribute _ is the property access interceptor, that is, the _ _ getattribute__ method of the class is automatically called when the property of the class is accessed by the instance.

When an instance calls a property, such as s1.name, it passes name into the _ _ getattribute__ method as an argument, and then returns the result of name processing after a series of operations.

As long as a class inheriting object is defined in Python, there is a property interceptor by default, but instead of doing anything after the interception, it returns directly. So we can overwrite the _ _ getattribute__ method to achieve related functions, such as viewing permissions, printing log logs, and so on.

two。 If _ _ getattribute__, is overridden, the class will call the overridden method, so the method must have a renturn return value and return the property passed in, otherwise the property call will fail.

3. Note that if you use the class name directly. The class property is called in the form of a class property, and the _ _ getattribute__ method is not called.

two。 Override _ _ getattribute__ to implement property interception function class Student (object): country = "china" # Class attributes are not put in _ _ dict__ def _ _ init__ (self,name,age): self.name = name self.age = age def _ _ getattribute__ (self, attr): # Note: attr is the passed property name Not the attribute value print ("start the property verification intercept function") print (attr) if attr = = "name": # Note that the original attribute name is referenced instead of self Just quote it in quotation marks. Print ("calling the name property now") elif attr = = "age": print ("calling the age property now") else: print ("calling other properties now") return object.__getattribute__ (self, attr) # returns the property name S1 = Student ("tom", 19) print (s1.name.s1.age S1.country)''the result is as follows: the start attribute verification intercept function name now calls the name attribute start attribute verification intercept function age now calls the age attribute start attribute verification interception function country now calls other attributes tom 19 china''' summary points:

1. The parameter passed in attribute _ (self,*args,**kwgs) is the attribute name, not the attribute value. Many beginners have misunderstandings.

two。 When a class property is called with a class name, the _ _ getattribute__ method is not passed, and only the instance object's call to the property is sought, including calling the class property.

3. Attribute _ attribute _ is an attribute interceptor. The attribute call will be processed, and finally a return value will be returned to the caller after processing the incoming attribute.

At this point, I believe you have a deeper understanding of "Python built-in attribute getattribute interceptor". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.