Fixed indentation and added error message for unlinked Summary file with distribcell paths in DataFrame

openmc/filter.py

@@ -629,6 +629,12 @@ class Filter(object):
             # Create Pandas Multi-index columns for each level in CSG tree
             if distribcell_paths:
 
+                # Distribcell paths require linked metadata from the Summary
+                if self.distribcell_paths is None:
+                    msg = 'Unable to construct distribcell paths since '
+                          'the Summary is not linked to the StatePoint'
+                    raise ValueError(msg)
+
                 # Make copy of array of distribcell paths to use in
                 # Pandas Multi-index column construction
                 distribcell_paths = copy.deepcopy(self.distribcell_paths)

openmc/mgxs/mgxs.py

@@ -2576,9 +2576,11 @@ class Chi(MGXS):
         xs_type: {'macro', 'micro'}
             Return macro or micro cross section in units of cm^-1 or barns.
             Defaults to 'macro'.
-    distribcell_paths : list of str
-        The paths traversed through the CSG tree to reach each distribcell
-        instance (for 'distribcell' filters only)
+        distribcell_paths : bool, optional
+            Construct columns for distribcell tally filters (default is True).
+            The geometric information in the Summary object is embedded into
+            a Multi-index column with a geometric "path" to each distribcell
+            instance.
 
         Returns
         -------