implementing shared_surfaces method. Not working

hub/city_model_structure/building.py

@@ -44,6 +44,7 @@ class Building(CityObject):
     self._appliances_electrical_demand = dict()
     self._domestic_hot_water_heat_demand = dict()
     self._eave_height = None
+    self._neighbours = None
     self._grounds = []
     self._roofs = []
     self._walls = []
@@ -441,3 +442,15 @@ class Building(CityObject):
       for usage in internal_zone.usages:
         _usage = f'{_usage}{usage.name}_{usage.percentage} '
     return _usage.rstrip()
+
+  def identify_shared_walls(self):
+    """
+    Identifies which building' walls adjoin the neighbouring building and saves that information in the
+    corresponding surfaces
+    """
+    for wall in self.walls:
+      percentage = 0
+      for building in self._neighbours:
+        for neighbour_wall in building.walls:
+          percentage += wall.shared_percentage(neighbour_wall)
+      wall.set_shared_percentage(percentage)