developing back end run methods

mdpow/analysis/ensemble.py

@@ -505,7 +505,7 @@ def _conclude_ensemble(self):
         pass  # pragma: no cover
 
     def run(self, start=None, stop=None, step=None):
-        """Runs _single_universe on each system and _single_frame
+        """Runs _single_universe on each system or _single_frame
         on each frame in the system.
 
         First iterates through keys of ensemble, then runs _setup_system
@@ -516,16 +516,17 @@ def run(self, start=None, stop=None, step=None):
         self._prepare_ensemble()
         for self._key in ProgressBar(self._ensemble.keys(), verbose=True):
             self._setup_system(self._key, start=start, stop=stop, step=step)
-            self._prepare_universe()
-            self._single_universe()
-            for i, ts in enumerate(ProgressBar(self._trajectory[self.start:self.stop:self.step], verbose=True,
+            try:
+                self._single_universe()
+            except NotImplementedError:
+                for i, ts in enumerate(ProgressBar(self._trajectory[self.start:self.stop:self.step], verbose=True,
                                                postfix=f'running system {self._key}')):
                 self._frame_index = i
                 self._ts = ts
                 self.frames[i] = ts.frame
                 self.times[i] = ts.time
                 self._single_frame()
-            self._conclude_universe()
+                raise
             logger.info("Moving to next universe")
         logger.info("Finishing up")
         self._conclude_ensemble()