Python 2.2 quick reference

Sometimes you want to associate a function with a particular class, but it doesn't always have an instance (self) to operate on. In these cases, you can declare a static method within the class. Such a method is like any other method, except that you won't include a first argument of self in the argument list. To make a method static, include a line of this form just after the method's declaration:

f = staticmethod ( f )

where f is the name of the method.

To call a static method, use this syntax:

C.f(...)

where C is the class name and f is the method name.

Here's an example. Suppose you have a class called Celsius that represents a temperature, and you want to be able to convert an object of that class to a 6-character string for display. Normally you would declare a .__str__() method in the class to do the conversion.

However, suppose you have a variable named outdoor that may contain a Celsius object, but sometimes the temperature is unknown and outdoor is set to None. You want to write a function that will convert the temperature if it is known, but render the value as '******' if not. You could write a standalone function that does that, but it really is associated with the class. So you write a static function like this:

class Celsius:
    ...
    def show(temp):
        if  temp is None:
            return '******'
        else:
            return str(temp)
    show  =  staticmethod(show)

Then you could call this method as "Celsius.show(outdoor)".