Init Plugin class vars per subclass

xblock/core.py

@@ -19,7 +19,7 @@
     HandlersMixin,
     XmlSerializationMixin,
 )
-from xblock.plugin import Plugin
+from xblock.plugin import Plugin, PluginMetaclass
 from xblock.validation import Validation
 
 
@@ -64,6 +64,7 @@ class XBlockMetaclass(
         ScopedStorageMixin.__metaclass__,
         RuntimeServicesMixin.__metaclass__,
         TagCombiningMetaclass,
+        PluginMetaclass,
 ):
     """
     Metaclass for XBlock.
@@ -182,10 +183,30 @@ def validate(self):
         return Validation(self.scope_ids.usage_id)
 
 
+class AsideMetaclass(
+        ScopedStorageMixin.__metaclass__,
+        RuntimeServicesMixin.__metaclass__,
+        PluginMetaclass,
+):
+    """
+    Metaclass for XBlock.
+
+    Combines all the metaclasses XBlocks needs:
+
+    * `ChildrenModelMetaclass`
+    * `ModelMetaclass`
+    * `TagCombiningMetaclass`
+
+    """
+    pass
+
+
 class XBlockAside(ScopedStorageMixin, RuntimeServicesMixin, HandlersMixin, Plugin):
     """
     This mixin allows Xblock-like class to declare that it provides aside functionality.
     """
+    __metaclass__ = AsideMetaclass
+
     entry_point = "xblock_asides.v1"
 
     @classmethod

xblock/plugin.py

@@ -43,6 +43,21 @@ def default_select(identifier, all_entry_points):
         raise AmbiguousPluginError(all_entry_points)
 
 
+class PluginMetaclass(type):
+    """
+    Initialize class vars per subclass
+    """
+    def __new__(mcs, name, bases, attrs):
+        """
+        Init the class vars
+        """
+        # Temporary entry points, for register_temp_plugin.  A list of pairs,
+        # (identifier, entry_point):
+        #   [('test1', test1_entrypoint), ('test2', test2_entrypoint), ...]
+        attrs['extra_entry_points'] = []
+        return super(PluginMetaclass, mcs).__new__(mcs, name, bases, attrs)
+
+
 class Plugin(object):
     """Base class for a system that uses entry_points to load plugins.
 
@@ -51,14 +66,10 @@ class Plugin(object):
         `entry_point`: The name of the entry point to load plugins from.
 
     """
+    __metaclass__ = PluginMetaclass
 
     entry_point = None  # Should be overwritten by children classes
 
-    # Temporary entry points, for register_temp_plugin.  A list of pairs,
-    # (identifier, entry_point):
-    #   [('test1', test1_entrypoint), ('test2', test2_entrypoint), ...]
-    extra_entry_points = []
-
     @classmethod
     def _load_class_entry_point(cls, entry_point):
         """