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 _scale_vars(s, v_list):
  """Scale all variables in v_list by s."""
  return [s * v for v in v_list]