Refs #9204 - Make sure new settings object is cleared ...

... whenever the singleton is reset.

Also, slight change so that we only ever load the instrument once on
interface startup.

Code/Mantid/MantidQt/CustomInterfaces/src/SANSRunWindow.cpp

@@ -314,9 +314,9 @@ void SANSRunWindow::initLocalPython()
   }
   runPythonCode("import ISISCommandInterface as i\nimport copy");
   runPythonCode("import isis_instrument\nimport isis_reduction_steps");
-  handleInstrumentChange();
 
   loadUserFile();
+  handleInstrumentChange();
 }
 /** Initialise some of the data and signal connections in the save box
 */
@@ -690,7 +690,7 @@ bool SANSRunWindow::loadUserFile()
     m_uiForm.mask_table->removeRow(i);
   }
 
-  QString pyCode = "i.ReductionSingleton.clean(isis_reducer.ISISReducer)";
+  QString pyCode = "i.Clean()";
   pyCode += "\ni.ReductionSingleton().set_instrument(isis_instrument.";
   pyCode += getInstrumentClass()+")";
   pyCode += "\ni.ReductionSingleton().user_settings =";
@@ -2362,7 +2362,6 @@ void SANSRunWindow::handleReduceButtonClick(const QString & typeStr)
   }
 
   //Reset the objects by initialising a new reducer object
-  //py_code = "i._refresh_singleton()";
   if (runMode == SingleMode) // TODO: test if it is really necessary to reload the file settings.
   {
   py_code = "\ni.ReductionSingleton.clean(isis_reducer.ISISReducer)";
@@ -2821,12 +2820,19 @@ void SANSRunWindow::handleInstrumentChange()
 
   //set up the required Python objects and delete what's out of date (perhaps everything is cleaned here)
   const QString instClass(getInstrumentClass());
-  QString pyCode("if i.ReductionSingleton().get_instrument() != '");
-  pyCode += m_uiForm.inst_opt->currentText()+"':";
-  pyCode += "\n\ti.ReductionSingleton.clean(isis_reducer.ISISReducer)";
-  pyCode += "\ni.ReductionSingleton().set_instrument(isis_instrument.";
-  pyCode += instClass+")";
-  runReduceScriptFunction(pyCode);
+
+  // Only set the instrument if it isn't alread set to what has been selected.
+  // This is useful on interface start up, where we have already loaded the user file
+  // and don't want to set the instrument twice.
+  const QString currentInstName = runPythonCode(
+    "print i.ReductionSingleton().get_instrument().name()").trimmed();
+  if( currentInstName != m_uiForm.inst_opt->currentText() )
+  {
+    QString pyCode("i.ReductionSingleton.clean(isis_reducer.ISISReducer)");
+    pyCode += "\ni.ReductionSingleton().set_instrument(isis_instrument.";
+    pyCode += instClass+")";
+    runReduceScriptFunction(pyCode);
+  }
 
   //now update the GUI
   fillDetectNames(m_uiForm.detbank_sel);

Code/Mantid/scripts/SANS/ISISCommandInterface.py

@@ -56,6 +56,13 @@ def issueWarning(msg):
 def _refresh_singleton():
     ReductionSingleton.clean(isis_reducer.ISISReducer)
     ReductionSingleton().remove_settings()
+
+def Clean():
+    """
+    An exposed command to allow cleaning of the reducer, and any related
+    settings.
+    """
+    _refresh_singleton()
 
 def UserPath(path):
     """

Code/Mantid/scripts/SANS/isis_reducer.py

@@ -133,6 +133,12 @@ def __getitem__(self, key):
         def __setitem__(self, key, value):
             self._prop_man()[key] = value
 
+        def __len__(self):
+            return len(self._prop_man())
+
+        def clear(self):
+            PropertyManagerDataService.remove(SETTINGS_PROP_MAN_NAME)
+
     return PropertyManagerPicklableWrapper()
 
 class Sample(object):
@@ -435,8 +441,11 @@ def deep_copy(self):
         return copy.deepcopy(current_settings)
 
     def remove_settings(self):
+        logger.debug("Clearing reducer settings.")
         global current_settings
         current_settings = None
+        self.settings.clear()
+        assert len(self.settings) == 0
 
     def cur_settings(self):
         """