Forgot to add this

sugar/p2p/model/AbstractModel.py

@@ -0,0 +1,10 @@
+class AbstractModel:
+	def __init__(self):
+		self._listeners = []
+	
+	def add_listener(self, listener):
+		self._listeners.append(listener)
+	
+	def _notify_model_change(self, key):
+		for listener in self._listeners:
+			listener(self, key)