Creating a static class with no instances

All of the tutorials I see online show how to create classes with __init__ constructor methods so one can declare objects of that type, or instances of that class.

How do I create a class (static in Java) so that I can access all methods and attributes of that class without having to create new instances/objects?

For example:

class World: allElems = [] def addElem(x): allElems.append(x) World.addElem(6) print(World.allElems) 

EDIT

class World(object): allAirports = [] @staticmethod def initialize(): f = open(os.path.expanduser("~/Desktop/1000airports.csv")) file_reader = csv.reader(f) for col in file_reader: allAirports.append(Airport(col[0],col[2],col[3])) 

error: name 'allAirports' is not defined

5 Answers

The Pythonic way to create a static class is simply to declare those methods outside of a class (Java uses classes both for objects and for grouping related functions, but Python modules are sufficient for grouping related functions that do not require any object instance). However, if you insist on making a method at the class level that doesn't require an instance (rather than simply making it a free-standing function in your module), you can do so by using the "@staticmethod" decorator.

That is, the Pythonic way would be:

# My module elements = [] def add_element(x): elements.append(x) 

But if you want to mirror the structure of Java, you can do:

# My module class World(object): elements = [] @staticmethod def add_element(x): World.elements.append(x) 

You can also do this with @classmethod if you care to know the specific class (which can be handy if you want to allow the static method to be inherited by a class inheriting from this class):

# My module class World(object): elements = [] @classmethod def add_element(cls, x): cls.elements.append(x) 

You could use a classmethod or staticmethod

class Paul(object): elems = [] @classmethod def addelem(cls, e): cls.elems.append(e) @staticmethod def addelem2(e): Paul.elems.append(e) Paul.addelem(1) Paul.addelem2(2) print(Paul.elems) 

classmethod has advantage that it would work with sub classes, if you really wanted that functionality.

module is certainly best though.

There are two ways to do that (Python 2.6+):

static method

class Klass(object): @staticmethod def static_method(): print "Hello World" Klass.static_method() 

module

your module file, called klass.py

def static_method(): print "Hello World" 

your code:

import klass klass.static_method() 

Ancient thread, but one way to make this work is:

class Static: def __new__(cls): raise TypeError('Static classes cannot be instantiated') 

Then, you can use it like so:

class Foo(Static): ... 

Seems the most 'Pythonic' to me, anyway.

Example use case: singleton class where I register handlers for conversion between types.

Cheers!

Seems that you need classmethod:

class World(object): allAirports = [] @classmethod def initialize(cls): if not cls.allAirports: f = open(os.path.expanduser("~/Desktop/1000airports.csv")) file_reader = csv.reader(f) for col in file_reader: cls.allAirports.append(Airport(col[0],col[2],col[3])) return cls.allAirports