Class method vs Static method in Python
The @classmethod decorator is a built-in function decorator that is an expression that gets evaluated after your function is defined. The result of that evaluation shadows your function definition.
A class method receives the class as an implicit first argument, just like an instance method receives the instance
class C(object): @classmethod def fun(cls, arg1, arg2, ...): .... fun: function that needs to be converted into a class method returns: a class method for function.
- A class method is a method that is bound to the class and not the object of the class.
- They have the access to the state of the class as it takes a class parameter that points to the class and not the object instance.
- It can modify a class state that would apply across all the instances of the class. For example, it can modify a class variable that will be applicable to all the instances.
A static method does not receive an implicit first argument.
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class C(object): @staticmethod def fun(arg1, arg2, ...): ... returns: a static method for function fun.
- A static method is also a method that is bound to the class and not the object of the class.
- A static method can’t access or modify the class state.
- It is present in a class because it makes sense for the method to be present in class.
Class method vs Static Method
- A class method takes cls as the first parameter while a static method needs no specific parameters.
- A class method can access or modify the class state while a static method can’t access or modify it.
- In general, static methods know nothing about the class state. They are utility-type methods that take some parameters and work upon those parameters. On the other hand class methods must have class as a parameter.
- We use @classmethod decorator in python to create a class method and we use @staticmethod decorator to create a static method in python.
When to use what?
- We generally use class method to create factory methods. Factory methods return class objects ( similar to a constructor ) for different use cases.
- We generally use static methods to create utility functions.
How to define a class method and a static method?
To define a class method in python, we use @classmethod decorator, and to define a static method we use @staticmethod decorator.
Let us look at an example to understand the difference between both of them. Let us say we want to create a class Person. Now, python doesn’t support method overloading like C++ or Java so we use class methods to create factory methods. In the below example we use a class method to create a person object from birth year.
As explained above we use static methods to create utility functions. In the below example we use a static method to check if a person is an adult or not.
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