adressing feature request rte-france#217

CHANGELOG.rst

@@ -43,6 +43,8 @@ Change Log
 - [ADDED] some handy argument in the `action_space.get_all_unitary_redispatch` and
   `action_space.get_all_unitary_curtail` (see doc)
 - [IMPROVED] prevent the use of the same instance of a backend in different environments
+- [IMPROVED] `Issue#217 <https://github.com/rte-france/Grid2Op/issues/217>`_ : no more errors when trying to
+  load a grid with unsupported elements (eg. 3w trafos or static generators) by PandaPowerBackend
 
 [1.5.2] - 2021-05-10
 -----------------------

grid2op/Space/GridObjects.py

@@ -1638,7 +1638,7 @@ def assert_grid_correct_cls(cls):
             raise IncorrectNumberOfSubstation("The number of substation is not consistent in "
                                               "self.sub_info (size \"{}\")"
                                               "and  self.n_sub ({})".format(len(cls.sub_info), cls.n_sub))
-        if np.sum(cls.sub_info) != cls.n_load + cls.n_gen + 2*cls.n_line + cls.n_storage:
+        if np.sum(cls.sub_info) != cls.n_load + cls.n_gen + 2 * cls.n_line + cls.n_storage:
             err_msg = "The number of elements of elements is not consistent between self.sub_info where there are "
             err_msg += "{} elements connected to all substations and the number of load, generators and lines in " \
                        "the _grid ({})."
@@ -1745,7 +1745,10 @@ def assert_grid_correct_cls(cls):
 
         # no empty bus: at least one element should be present on each bus
         if np.any(cls.sub_info < 1):
-            raise BackendError("There are {} bus with 0 element connected to it.".format(np.sum(cls.sub_info < 1)))
+            # raise BackendError("There are {} bus with 0 element connected to it.".format(np.sum(cls.sub_info < 1)))
+            warnings.warn(f"There are {np.sum(cls.sub_info < 1)} substations where  no 'controlable' elements "
+                          f"are connected. These substations will be used in the computation of the powerflow "
+                          f"(by the backend) but you will NOT be able to control anything on them.")
 
         # redispatching / unit commitment
         if cls.redispatching_unit_commitment_availble:

grid2op/data_test/5bus_modif_grid/config.py

@@ -0,0 +1,19 @@
+from grid2op.Action import TopologyAction
+from grid2op.Reward import L2RPNReward
+from grid2op.Rules import DefaultRules
+from grid2op.Chronics import Multifolder
+from grid2op.Chronics import GridStateFromFileWithForecasts
+from grid2op.Backend import PandaPowerBackend
+
+config = {
+    "backend": PandaPowerBackend,
+    "action_class": TopologyAction,
+    "observation_class": None,
+    "reward_class": L2RPNReward,
+    "gamerules_class": DefaultRules,
+    "chronics_class": Multifolder,
+    "grid_value_class": GridStateFromFileWithForecasts,
+    "volagecontroler_class": None,
+    "thermal_limits": None,
+    "names_chronics_to_grid": None
+}