Difference between staticmethod and classmethod

Question

What is the difference between a function decorated with @staticmethod and one decorated with @classmethod?

Answer 1

Another consideration with respect to staticmethod vs classmethod comes up with inheritance. Say you have the following class:

class Foo(object):
    @staticmethod
    def bar():
        return "In Foo"

And you then want to override bar() in a child class:

class Foo2(Foo):
    @staticmethod
    def bar():
        return "In Foo2"

This works, but note that now the bar() implementation in the child class (Foo2) can no longer take advantage of anything specific to that class. For example, say Foo2 had a method called magic() that you want to use in the Foo2 implementation of bar():

class Foo2(Foo):
    @staticmethod
    def bar():
        return "In Foo2"
    @staticmethod
    def magic():
        return "Something useful you'd like to use in bar, but now can't" 

The workaround here would be to call Foo2.magic() in bar(), but then you're repeating yourself (if the name of Foo2 changes, you'll have to remember to update that bar() method).

To me, this is a slight violation of the open/closed principle, since a decision made in Foo is impacting your ability to refactor common code in a derived class (ie it's less open to extension). If bar() were a classmethod we'd be fine:

class Foo(object):
    @classmethod
    def bar(cls):
        return "In Foo"

class Foo2(Foo):
    @classmethod
    def bar(cls):
        return "In Foo2 " + cls.magic()
    @classmethod
    def magic(cls):
        return "MAGIC"

print Foo2().bar()

Gives: In Foo2 MAGIC