Synnefo

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class ArgBasedSingletonMeta(type):

    """Implement the Singleton pattern with a twist.

    Implement the Singleton pattern with a twist:

    The uniqueness on the object is based on the class name,

    plus the argument list (args and kwargs).

    Unique objects are store in the '_singles' class attribute.

    A distinct _singles object is used per subclass.

    """

    def __call__(cls, *args, **kwargs):

        kwlist = str([(k, kwargs[k]) for k in sorted(kwargs.keys())])

        distinct = str((cls, args, kwlist))

        # Allocate a new _singles attribute per subclass

        if not hasattr(cls, "_singles_cls") or cls != cls._singles_cls:

            cls._singles = {}

            cls._singles_cls = cls

        if distinct not in cls._singles:

            obj = super(ArgBasedSingletonMeta, cls).__call__(*args, **kwargs)

            cls._singles[distinct] = obj

        ret = cls._singles[distinct]

        return ret

class ArgBasedSingleton(object):

    __metaclass__ = ArgBasedSingletonMeta