Meaning of @classmethod and @staticmethod for beginner

python

classmethod

staticmethod

decorators

byNikita Barsukov·Aug 15, 2024

In Python, @classmethod morphs a regular function into a class method. This means it obtains the class (cls) as an implicit first argument, giving it the ability to meddle with class state. On the other side, @staticmethod crafts a method which is conceptually bound to the class but doesn't meddle with any instance or class itself.

Here's a quick example:

class MyClass:
    @classmethod
    def cls_method(cls):
        return 'class method called', cls
    
    @staticmethod
    def static_method():
        return 'static method called'

# Usage
print(MyClass.cls_method())    # Output: ('class method called', <class '__main__.MyClass'>)
print(MyClass.static_method()) #'static method called', says it with a static voice!

Always remember, use @classmethod to mingle with class attributes or methods. @staticmethod, however, meets the mark when the method doesn't interact with class or instances.

The Devil is in the Details

Unraveling @classmethod

@classmethod is the secret ingredient for factory methods that create new objects, using cls to create instances, lifting the correct subclass off the production line. For instance, let's suppose the method Date.from_string cranks out a Date instance from a string. Addition of an alternative constructor through @classmethod? Check.

Then there is the mistress of inheritance advantage: @classmethod respects the hierarchy of inheritance, letting sub-classes piggyback on the existing class method and even make it dance to their own tune. No need for a rewrite!

Decrypting @staticmethod

@staticmethod is used when the method behaves like a model citizen, playing nice with the class but never really meddling with it. It doesn’t need access to any class or instance data, making it ideal for utility functions. Take Date.is_date_valid, for instance. Performing a straightforward check that doesn't care for the state of an instance? Yes, please!

When to crown each one

Polish your @classmethod crown if:

Class object is your wingman in calling other class methods or constructors.
Inheritance and overriding of subclasses is not just an option but a necessity.

Don your @staticmethod sunglasses if:

Functionality doesn’t meddle with but is logically tied to the class.
Polluting global namespace with class-related functions is a big no.

Pitfalls to Dodge and Practices to Adopt

Code cohesion and organization

Just like a ringmaster commands the performance, @staticmethod enhances code cohesion by gathering related utilities under one class canopy. Although they don’t mingle with class or instance-specific data, they contribute to a more organized performance!

Abandoning hard-coded class references

Dropping the habit of hard-coded class references by embracing @classmethod is like finding the ideal parking spot at the mall - a game changer! This ensures your class hierarchy retains its complexity and charm, and subclasses can extend functionality without spawning new methods.

Testing becomes a cakewalk

Both sisters @classmethod and @staticmethod are a godsend for improving the testability of your rig. Unit tests become more modular and focused, as dependencies on class and instance state are shown the backseat.

Python’s standard library is a gold mine

Python's standard library is the Holy Grail of innate wisdom on these decorators. str.maketrans is a class act of @staticmethod. It mixes up a translation table apt for str.translate, yet such creative process does not hover about any specific string instance.

Self-explanatory code and simple access

With @classmethod and @staticmethod you’re getting self-documenting code. They act like neon signs for other programmers, highlighting the intent and scope of the method - does it meddle with the class state or is it just a static utility?

Moreover, both can be invoked directly on the class without needing an instance, like so: ClassName.method(), saving you from churning out objects unnecessarily. Smooth sailing!

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