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 reorder_item(self, item, position):
    new_position = min(max(position, 0), len(self._items) - 1)