code: def _unpack_case(self, case):
          
          base_mva = case.base_mva
          b = case.connected_buses
          l = case.online_branches
          g = case.online_generators
          nb = len(b)
          nl = len(l)
          ng = len(g)
  
          return b, l, g, nb, nl, ng, base_mva
docs: Returns the contents of the case to be used in the OPF.