Added stricter controls over the returned values by the datasource.

Created by: stefanoborini

The datasource must return a list of DataValues. This PR enforces the types of both the returned entity and its content.

force_bdss/core_evaluation_driver.py

@@ -145,7 +145,7 @@ def _compute_layer_results(environment_data_values,
 
         if not isinstance(res, list):
             error_txt = (
-                "The run method of data source {} must return a list." 
+                "The run method of data source {} must return a list."
                 " It returned instead {}. Fix the run() method to return"
                 " the appropriate entity.".format(
                     factory.name,
@@ -197,7 +197,6 @@ def _compute_layer_results(environment_data_values,
                 log.error(error_txt)
                 raise RuntimeError(error_txt)
 
-
         # At this point, the returned data values are unnamed.
         # Add the names as specified by the user.
         for dv, output_slot_info in zip(res, model.output_slot_info):