add a couple comments to describe why the error cases are there..

ui/server.py

@@ -44,9 +44,9 @@ class MEDAServer:
 		try:
 			id = uuid.UUID(id)
 			return self._objstore[id][-1].encode()
-		except ValueError:
+		except ValueError:	# invalid format for uuid
 			request.setResponseCode(400)
-		except KeyError:
+		except KeyError:	# no object
 			request.setResponseCode(404)
 
 	@app.route('/store')