Singleton Utility

The singleton utility provides a class decorator, allowing to easily create singleton classes.

class xobox.utils.singleton.Singleton(decorated)

Decorator class to turn any other class into a lazy singleton.

This class must be applied as a decorator instead of inheriting from this class.

Restrictions

• The decorated class can define one __init__ function, but this constructor is restricted to the self, *args and **kwargs arguments (in fact those must be present).
• To get the singleton instance, the get_instance() method has to be used. Trying to use __call__ will result in a TypeError being raised.
• The actual instance will not be created before get_instance() has been called (lazy behaviour).
• The decorated class cannot be inherited from. Therefore, this decorator can only be applied to final classes.
• This decorator shows good manners and takes care of __doc__, __module__, __name__, __annotations__ and __qualname__ context of the decorated class. This allows care-free handling in conjunction with automated documentation extraction tools such as Sphinx autodoc or similar.

Parameters:decorated – The Python class to be wrapped.

get_instance(*args, **kwargs)

Returns the singleton instance. Upon its first call, it creates a new instance of the decorated class and calls its __init__ method. On all subsequent calls, the already created instance is returned. :param args: positional arguments to be passed to the wrapped class’ constructor :param kwargs: keyword arguments to be passed to the wrapped class’ constructor :return: instance of the singleton-decorated class.