diff --git a/cura/Settings/ExtruderManager.py b/cura/Settings/ExtruderManager.py
index 12277f9641..0ffaca4992 100755
--- a/cura/Settings/ExtruderManager.py
+++ b/cura/Settings/ExtruderManager.py
@@ -41,7 +41,7 @@ class ExtruderManager(QObject):
     def __init__(self, parent = None):
         super().__init__(parent)
         self._extruder_trains = { } #Per machine, a dictionary of extruder container stack IDs. Only for separately defined extruders.
-        self._active_extruder_index = -1
+        self._active_extruder_index = -1 # Indicates the index of the active extruder stack. -1 means no active extruder stack
         self._selected_object_extruders = []
         Application.getInstance().globalContainerStackChanged.connect(self.__globalContainerStackChanged)
         self._global_container_stack_definition_id = None
@@ -74,15 +74,18 @@ class ExtruderManager(QObject):
         except KeyError:
             return 0
 
+    ##  Gets a dict with the extruder stack ids with the extruder number as the key.
+    #   The key "-1" indicates the global stack id.
+    #
     @pyqtProperty("QVariantMap", notify = extrudersChanged)
     def extruderIds(self):
-        map = {}
+        extruder_stack_ids = {}
         global_stack_id = Application.getInstance().getGlobalContainerStack().getId()
-        map["-1"] = global_stack_id
+        extruder_stack_ids["-1"] = global_stack_id
         if global_stack_id in self._extruder_trains:
             for position in self._extruder_trains[global_stack_id]:
-                map[position] = self._extruder_trains[global_stack_id][position].getId()
-        return map
+                extruder_stack_ids[position] = self._extruder_trains[global_stack_id][position].getId()
+        return extruder_stack_ids
 
     @pyqtSlot(str, result = str)
     def getQualityChangesIdByExtruderStackId(self, id: str) -> str:
@@ -516,7 +519,8 @@ class ExtruderManager(QObject):
         result = []
         machine_extruder_count = global_stack.getProperty("machine_extruder_count", "value")
 
-        if machine_extruder_count is 1:
+        # In case the printer is using one extruder, shouldn't exist active extruder stacks
+        if machine_extruder_count == 1:
             return result
 
         if global_stack and global_stack.getId() in self._extruder_trains:
@@ -537,7 +541,7 @@ class ExtruderManager(QObject):
             if self._active_extruder_index == -1:
                 self.setActiveExtruderIndex(0)
         else:
-            if self._active_extruder_index > -1:
+            if self._active_extruder_index != -1:
                 self.setActiveExtruderIndex(-1)
 
         self.activeExtruderChanged.emit()
diff --git a/cura/Settings/MachineManager.py b/cura/Settings/MachineManager.py
index 9ce288e0c0..69cebc26c0 100755
--- a/cura/Settings/MachineManager.py
+++ b/cura/Settings/MachineManager.py
@@ -545,6 +545,10 @@ class MachineManager(QObject):
 
         return result
 
+    ##  Gets a dict with the active materials ids set in all extruder stacks and the global stack
+    #   (when there is one extruder, the material is set in the global stack)
+    #
+    #   \return The material ids in all stacks
     @pyqtProperty("QVariantMap", notify = activeMaterialChanged)
     def allActiveMaterialIds(self) -> Dict[str, str]:
         result = {}