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introduction

This article is my right to python The static method inside （staticmethod） and Class method （classmethod） Some insights , I hope I can help you . Before preparing to write this article, I was also very confused , Always don't understand , muddle along , Just understand the code , It's not often used anyway , I didn't care . But recently, due to the needs of the project , The full screen static methods and class methods are true, which makes me a little confused , What do I do , Want to continue , Then you have to learn . Don't push yourself , Never know your potential .

A relatively simple and rough way to distinguish ： To decide whether to use @staticmethod still @classmethod, You have to look inside class methods . If your method accesses other variables in the class / Method , So use @classmethod. On the other hand , If the method does not touch any other variables in the class , So use @staticmethod.
But its design has a deeper logical connection :
classmethod Mainly used to replace constructors .
staticmethod Do not use the state of the object , Don't even use the structure of the class itself . It can be a function outside a class . It is only placed inside the class , Used to group functions with similar functions （ for example , image Java Mathematical static methods ）

@classmethod
Person.printAge = classmethod(Person.printAge)

@staticmethod
Calculator.add_numbers = staticmethod(Calculator.add_numbers)

Can understand these two lines of code , You should be able to understand what static methods are , What is a class method . Of course , It doesn't matter if you don't understand , Let's explain in detail through chestnuts \

@classmethod

What is a class method ？

What is a class method ？
A class method is a method bound to a class rather than its object . It does not need to create class instances , It's like staticmethod equally .

The difference between static methods and class methods is ：

Static methods know nothing about classes , Process parameters only
Class methods apply to classes , Because its parameters are always the class itself .
Class methods can be called by classes and their objects .

Class.classmethod()
Class().classmethod()

But anyway ,class Methods are always attached to a class , The first parameter is the class itself .cls

def classMethod(cls, args…)

Example 1

Code ：

class Person:
age = 25
def printAge(cls):
print('The age is:', cls.age)
Person.printAge = classmethod(Person.printAge)
Person.printAge()

result ：

Code ：

class Person:
age = 25
@classmethod
def printAge(cls):
print('The age is:', cls.age)
Person.printAge()

result ：

You will find that the code has changed , But the result is the same . If you are careful, you will find , you 're right , In code
****@classmethod Equivalent to Person.printAge = classmethod(Person.printAge)

Instance methods can call instance methods 、 Class method 、 Static methods . Class objects can only call class methods 、 Static methods .

classmethod And staticmethod Usage is similar. ,classmethod Can pass staticmethod Instead of , When called through a class , The two are indistinguishable from each other for the caller . The difference between the two is that ,classmethod Added a reference to the actual calling class .
🥭🥭 Method can determine that it is called through the base class , Or is it called through a subclass
🥭🥭 When called through subclasses , Method can return instances of subclasses instead of base classes
🥭🥭 When called through subclasses , Method can call other of the subclass classmethod

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