Difference between `@staticmethod` and `@classmethod` function decorators in Python
Difference between `@staticmethod` and `@classmethod` function decorators in Python
David Y.
—The Problem
What is the difference between a function decorated with @staticmethod and one decorated with @classmethod in Python?
The Solution
Python programmers who have used classes will know that standard methods inside a class receive the called instance as their first argument. This is conventionally called self and must be specified as a parameter, per the Python principle that “explicit is better than implicit”. The following code snippet shows an example of this:
class Greeter: def __init__(self, name): self.name = name def say_hello(self): print(f"Hello, my name is {self.name}.") alice = Greeter("Alice") alice.say_hello() # will print "Hello, my name is Alice."
Functions decorated by @staticmethod or @classmethod provide alternatives to this behavior. We can decorate a function with @staticmethod to prevent Python from passing an instance of the object to it, as below.
class Greeter: def __init__(self, name): self.name = name @staticmethod def say_hello_static(name): # <-- no self parameter print(f"Hello {name}, how are you?") alice = Greeter("Alice") alice.say_hello_static("Bob") # will print "Hello Bob, how are you?"
This can be useful when we have functionality that logically belongs in a given class, but does not do anything with the instance it’s called on.
By contrast, the @classmethod decorator will make Python pass the class of the instance it’s called on as the first argument. By convention, the first parameter of a class method is called cls. Class methods can also be called on classes directly.
class Greeter: @classmethod def say_hello_class(cls): # <-- cls instead of self print(f"Hello, I am a {cls.__name__}.") Greeter.say_hello_class() # will print "Hello, I am a Greeter." alice = Greeter() alice.say_hello_class() # will print "Hello, I am a Greeter."
Class methods are useful when we want to define behaviors that affect a class as a whole, rather than single instances. A common use case is creating factory methods.
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