A bit more pythonic way of using the items callback in node categories. The category.items attribute is now a function taking a context parameter instead of a property. This can be used for checking validity, e.g. for doing node group recursion checks, and filter out unusable items.

release/scripts/modules/nodeitems_utils.py

@@ -26,21 +26,17 @@ class NodeCategory():
     def poll(cls, context):
         return True
 
-    @property
-    def items(self):
-        if hasattr(self, '_items'):
-            return self._items
-        elif hasattr(self, '_itemfunc'):
-            return self._itemfunc(self)
-
-    def __init__(self, identifier, name, description="", items=[]):
+    def __init__(self, identifier, name, description="", items=None):
         self.identifier = identifier
         self.name = name
         self.description = description
-        if callable(items):
-            self._itemfunc = items
+
+        if items is None:
+            self.items = lambda context: []
+        elif callable(items):
+            self.items = items
         else:
-            self._items = items
+            self.items = lambda context: items
 
 class NodeItem():
     def __init__(self, nodetype, label=None, settings={}):
@@ -69,7 +65,7 @@ def register_node_categories(identifier, cat_list):
         layout = self.layout
         col = layout.column()
         default_context = bpy.app.translations.contexts.default
-        for item in self.category.items:
+        for item in self.category.items(context):
             op = col.operator("node.add_node", text=item.label, text_ctxt=default_context)
             op.type = item.nodetype
             op.use_transform = True