Forgot that 3.6 does not support lru_cache without ()

src/calng/SimpleAssembler.py

@@ -182,7 +182,7 @@ class SimpleAssembler(TrainMatcher.TrainMatcher):
         self._buffered_status_update.set("rate", self._rate_tracker.get())
         self.set(self._buffered_status_update)
 
-    @functools.lru_cache
+    @functools.lru_cache()
     def _source_to_index(self, source):
         # note: cache means warning only shows up once (also not performance-critical)
         # TODO: allow user to inspect, modify the mapping