def __init__(self, groups=None):
        super(GroupedRequirements, self).__init__(NamedRequirements)
        self.groups = groups or self.default_groups
        self.filename = None
        self.create_default_groups()
def memoized(*args):
        try:
            return stored_results[args]
        except KeyError:
            result = stored_results[args] = fn(*args)
            return result