Static methods and class members in Python

Preface

Because the level of Python is currently in the usable stage, the scripts I usually write using Python are relatively simple, and I have never written a slightly larger project. There is still a lack of understanding of classes in Python, the organizational relationships between classes, and how classes are coupled in the entire project. I plan to read Python code written by others to learn the application of Python in engineering and improve my technical level. The selected Python code is the Python crawler code, github address. This code just meets the level of code that is out of my comfort zone, so it is very suitable for my current level to learn.

After Python2.4, decorators are mainly used to implement static methods and class methods.

The decorator uses the @ operator, the example is as follows:

class Example:
 val1 = "Value 1"
 def __init__(self):
 self.val2 = "Value 2"

 @staticmethod
 def staticmd():
 print("静态方法，无法访问Value1和Value2")

 @classmethod
 def classmd(cls):
 print('类方法，类：'+str(cls)+",val1:"+cls.val1+",无法访问val2的值")


example = Example()
example.staticmd() #实例调用静态方法，无法访问实例变量val1和val2
example.classmd() #实例调用类方法，输出结果：类方法，类：<class &#39;__main__.Example&#39;>,val1:Value 1,无法访问val2的值
Example.classmd() #类调用类方法，输出结果：类方法，类：<class &#39;__main__.Example&#39;>,val1:Value 1,无法访问val2的值
example.val1 = "The instance value1 changed"
example.classmd() #类调用类方法，输出结果：类方法，类：<class &#39;__main__.Example&#39;>,val1:Value 1,无法访问val2的值
Example.val1 = "The class value2 changed"
example.classmd() #类调用类方法，输出结果：类方法，类：<class &#39;__main__.Example&#39;>,val1:The class value2 changed,无法访问val2的值
Example.classmd() #类调用类方法，输出结果：类方法，类：<class &#39;__main__.Example&#39;>,val1:The class value2 changed,无法访问val2的值

I believe it is obvious from the above example Distinguish the difference between static methods and class methods.

The first is the difference in syntax:

• Static methods do not need to pass in the self parameter, and class member methods need to pass in the cls parameter representing this class;

• Static methods can access instance variables and class variables. Class member methods cannot access instance variables but can access class variables

Used Difference:

Since static methods cannot access class attributes, instance attributes are equivalent to a relatively independent method and have nothing to do with the class. In this way, static methods are just functions in the scope of the class.

For more articles related to static methods and class members in Python, please pay attention to the PHP Chinese website!