when gui loads a file, guess at default variable

If we had a file open in that "slot" (A or B) already, and the selected variable name is also present in the new file, pick that.
If that doesn't work, check to see if the selected variable name in the other file (B or A) is present, and if so pick that.
Otherwise stick with the existing default: the first item.

This should speed things up a little bit when bouncing between files, as the variable the user is most likely interested will already be selected.

pyglance/glance/gui_view.py

@@ -252,7 +252,7 @@ class GlanceGUIView (QtGui.QWidget) :
         variableSelection = QtGui.QComboBox()
         variableSelection.setDisabled(True)
         variableSelection.currentIndexChanged.connect(partial(self.reportVariableSelected, file_prefix=file_prefix))
-        variableSelection.lastSelected = None
+        variableSelection.lastSelected = "InvalidStringThatShouldNeverExist"
         self.widgetInfo[file_prefix]['variable'] = variableSelection
         grid_layout.addWidget(variableSelection, currentRow, 2, 1, 3)
         
@@ -891,13 +891,32 @@ class GlanceGUIView (QtGui.QWidget) :
         
         # if we got a new variable list, set up the appropriate drop down list
         if variable_list is not None :
+            # Cache now, because clear/addItems will change it as a side effect
+            last_selected = self.widgetInfo[file_prefix]['variable'].lastSelected
+
             # set up the list of selectable variables for analysis
             self.widgetInfo[file_prefix]['variable'].clear()
             self.widgetInfo[file_prefix]['variable'].addItems(variable_list)
+
+            # If the new file has the same variable name we were just
+            # displaying, default to it.
+            i = self.widgetInfo[file_prefix]['variable'].findText(last_selected)
+            if i != -1:
+                selected_variable = last_selected
+            else:
+                # That didn't work? Well, can we find a variable name
+                # matching what the other field is displaying?
+                if file_prefix == A_CONST: other = B_CONST
+                else:                      other = A_CONST
+                other_string = self.widgetInfo[other]['variable'].currentText()
+                i = self.widgetInfo[file_prefix]['variable'].findText(other_string)
+                if i != -1:
+                    selected_variable = last_selected
         
         # set the selected variable
         tempPosition = self.widgetInfo[file_prefix]['variable'].findText(selected_variable)
         self.widgetInfo[file_prefix]['variable'].setCurrentIndex(tempPosition)
+        self.widgetInfo[file_prefix]['variable'].lastSelected = selected_variable
         
         # set the override
         self.widgetInfo[file_prefix]['override'].setChecked(use_fill_override)