mend

src/feature-extractor/sample.py

@@ -88,11 +88,15 @@ class Sample:
     def __setitem__(self, key, value):
         vals = key.split(".")
         if 1 == len(vals):
+            if key in self.__general:
+                raise ValueError('Property \"%s\" is already set.' % key)
             self.__general[key] = value
         elif 2 == len(vals) and Sample.__is_valid_prefix(vals[0]):
+            if vals[1] in self.__activities[vals[0]]:
+                raise ValueError('Property \"%s\" is already set.' % key)
             self.__activities[vals[0]][vals[1]] = value
         else:
-            raise ValueError('Unable to access value at %s, unknown prefix.' % key)
+            raise ValueError('Unable to access key \"%s\", unknown prefix.' % key)
 
     def __contains__(self, key):
         vals = key.split(".")