change sort key on the class (not the instances)

grum/dictlist/dictlistitem.py

@@ -12,13 +12,16 @@ class DictListItem(QListWidgetItem):
         self.key = key
         self.value = value
         self.set_alarm(False)
-        self._sort_key = None
 
 
-    def set_sort_key(self, sk):
-        self._sort_key = sk
+    _sort_key = None
+
+    @classmethod
+    def set_sort_key(cls, sk):
+        cls._sort_key = staticmethod(sk) # need to attach as staticmethod, otherwise self is inserted as first argument
 
     def __lt__(self, other):
+        assert self._sort_key == other._sort_key
         sk = self._sort_key
         if sk:
             return sk(self) < sk(other)

grum/dictlist/dictlistwidget.py

@@ -73,8 +73,7 @@ class DictListWidget(QListWidget):
 
 
     def set_sort_key(self, sk):
-        for i in self.items.values():
-            i.set_sort_key(sk)
+        DictListItem.set_sort_key(sk)
 
         if sk is None:
             self.setSortingEnabled(False)