Python Cookbook

Implementing Static Methods

Credit: Alex Martelli, Carel Fellinger

Problem

You want to call methods directly on a class without supplying an instance of the class as the first argument, or on any instance without having the instance implicitly become the first argument.

Solution

In Python 2.2 (on either classic or new-style classes), the new built-in staticmethod function wraps any callable into a static method, and we just bind the same name to the staticmethod object in class scope:

class Greeter:
    def greet(name): print "Hello", name
    greet = staticmethod(greet)

In Python 2.1 and earlier, we can easily simulate the same construct:

class staticmethod:
    def _ _init_ _(self, anycallable): self._ _call_ _ = anycallable

Now, with any release of Python, we can say:

>>> greeting = Greeter(  )
>>> greeting.greet("Peter")
Hello Peter
>>> Greeter.greet("Paul")
Hello Paul

You can get a static method as a class attribute or as the attribute of any instance of the class. It does not matter which, because when you call the static method, it calls the underlying callable anyway.

Discussion

In Python, when you want to make a function available for calling, you normally expose it as an attribute of a module, not of a class. An attribute of a class object that starts out as a Python function implicitly mutates into an unbound method (see Recipe 5.13 for a way to exploit this). Thus, if you want to make the function available as a class attribute, without mutation, you need to wrap the function into a callable ...