Collection of useful functions and patterns for Python

utils.py

class Singleton(object):
    """
    Decorator for the singletton pattern in Python: http://stackoverflow.com/q/31875

    Usage::

        >>> @Singleton
            class MyClassSingleton(object): pass

        >>> instance = MyClassSingleton.instance
    """

    def __init__(self, decorated):
        self.__decorated = decorated

    @property
    def instance(self):
        try:
            return self.__instance
        except AttributeError:
            self.__instance = self.__decorated()
            return self.__instance

    def __call__(self):
        raise TypeError('Singleton must be accessed through instance property')

    def __instancecheck__(self, instance):
        return isinstance(instance, self.__decorated)


def flatten(x):
    """
    Returns a flatten tuple out of a nested structure of lists and tuples::

        >>> flatten([1,2,3,(4,5,[6]),[7,8,9]])
        (1, 2, 3, 4, 5, 6, 7, 8, 9)
    """
    return sum(map(flatten, x), ()) if isinstance(x, (tuple, list)) else (x,)