[1.x] Backport #17772

python/mxnet/module/executor_group.py

@@ -308,8 +308,16 @@ def decide_slices(self, data_shapes):
     def _collect_arrays(self):
         """Collect internal arrays from executors."""
         # convenient data structures
-        self.data_arrays = [[(self.slices[i], e.arg_dict[name]) for i, e in enumerate(self.execs)]
-                            for name, _ in self.data_shapes]
+
+        # check if self.slices is populated, if not then that means that there is no batch size
+        if self.slices:
+            # based on batch size, slice up data for the given contexts (self.execs)
+            self.data_arrays = [[(self.slices[i], e.arg_dict[name]) for i, e in enumerate(self.execs)]
+                                for name, _ in self.data_shapes]
+        else:
+            # just use the context index as index into the data
+            self.data_arrays = [[(slice(i, i+1), e.arg_dict[name]) for i, e in enumerate(self.execs)]
+                                for name, _ in self.data_shapes]
 
         self.state_arrays = [[e.arg_dict[name] for e in self.execs]
                              for name in self.state_names]