Python: thinking of a module and its variables as a singleton — Clean approach?

Question

I\'d like to implement some sort of singleton pattern in my Python program. I was thinking of doing it without using classes; that is, I\'d like to put all the singleton-rel

Answer 1

For a legitimate Singleton:

class SingletonMeta(type):
    __classes = {} # protect against defining class with the same name
    def __new__(cls, cls_name, cls_ancestors, cls_dict): 
         if cls_name in cls.__classes:
             return cls.__classes[cls_name]
         type_instance = super(SingletonMeta, cls).__new__(cls, cls_name, cls_ancestors, cls_dict) # pass 'type' instead of 'cls' if you dont want SingletonMeta's attributes reflected in the class
         return type_instance() # call __init__

class Singleton:
    __metaclass__ = SingletonMeta
    # define __init__ however you want

    __call__(self, *args, *kwargs):
        print 'hi!'

To see that it truly is a singleton, try to instantiate this class, or any class that inherits from it.

singleton = Singleton() # prints "hi!"