Move empty inst check to method on inst object

scripts/Diffraction/isis_powder/abstract_inst.py

@@ -80,6 +80,12 @@ class AbstractInst(object):
             self._beam_parameters = {'height': height,
                                      'width': width}
 
+    def should_subtract_empty_inst(self):
+        """
+        :return: Whether the empty run should be subtracted from a run being focused
+        """
+        return True
+
     # Mandatory overrides
 
     def _get_run_details(self, run_number_string):

scripts/Diffraction/isis_powder/pearl.py

@@ -67,6 +67,9 @@ class Pearl(AbstractInst):
                                                              cross_correlate_params=cross_correlate_params,
                                                              get_det_offset_params=get_detector_offsets_params)
 
+    def should_subtract_empty_inst(self):
+        return self._inst_settings.subtract_empty_inst
+
     @contextmanager
     def _apply_temporary_inst_settings(self, kwargs):
         self._switch_long_mode_inst_settings(kwargs.get("long_mode"))

scripts/Diffraction/isis_powder/routines/focus.py

@@ -25,9 +25,7 @@ def _focus_one_ws(input_workspace, run_number, instrument, perform_vanadium_norm
         _test_splined_vanadium_exists(instrument, run_details)
 
     # Subtract empty instrument runs, as long as this run isn't an empty and user hasn't turned empty subtraction off
-    if not common.runs_overlap(run_number, run_details.empty_runs) and \
-            (not hasattr(instrument._inst_settings, "subtract_empty_inst") or
-             instrument._inst_settings.subtract_empty_inst):
+    if not common.runs_overlap(run_number, run_details.empty_runs) and instrument.should_subtract_empty_inst():
         input_workspace = common.subtract_summed_runs(ws_to_correct=input_workspace, instrument=instrument,
                                                       empty_sample_ws_string=run_details.empty_runs)