Singleton with Metaclass
Singletons get a bad wrap but they can often be useful when used properly. I came across this pattern for implementing them in Python a couple of years back, it worked well in 2.7 but may be out of date for 3.
class Singleton(type):def __init__(cls, name, bases, dict):super(Singleton, cls).__init__(name, bases, dict)cls._instance = Nonedef __call__(cls, *args, **kw):if cls._instance is None:cls._instance = super(Singleton, cls).__call__(*args, **kw)return cls._instance
This can now be implemented in any class you wish to make singleton like so:
class SingleInstance():__metaclass__ = Singletondef __init__(self):passdef __str__(self):return 'SingleInstance'