comment on road grade; exception handling on unpickling

flow/energy_models/base_energy.py

@@ -10,6 +10,9 @@ class BaseEnergyModel(metaclass=ABCMeta):
     vehicle type: whether EV or Combustion Engine, Toyota Prius or Tacoma
     or non-Toyota vehicles. Non-Toyota vehicles are set by default
     to be an averaged-size vehicle.
+
+    Note: road grade is included as an input parameter, but the
+    functional dependence on road grade is not yet implemented.
     """
 
     def __init__(self):

flow/energy_models/toyota_energy.py

@@ -14,8 +14,15 @@ def __init__(self, filename):
         # download file from s3 bucket
         s3 = boto3.client('s3')
         s3.download_file('toyota.restricted', filename, 'temp.pkl')
+
         with open('temp.pkl', 'rb') as file:
-            self.toyota_energy = pickle.load(file)
+            try:
+                self.toyota_energy = pickle.load(file)
+            except TypeError:
+                print('Must use Python version 3.6.8 to unpickle')
+                # delete pickle file
+                os.remove(file)
+                raise
 
         # delete pickle file
         os.remove(file)