diff --git a/dictdata.py b/dictdata.py
index 5ef8d2d..f4d338b 100644
--- a/dictdata.py
+++ b/dictdata.py
@@ -1,4 +1,7 @@
 import plugin
+class ReadOnlyError(Exception):
+	pass
+
 class DictData(plugin.JSONData):
 	def __init__(self,filename,**kwargs):
 		plugin.JSONData.__init__(self,kwargs)
@@ -14,3 +17,15 @@ class DictData(plugin.JSONData):
 		return k in self.value
 	def get(self,k,default=None):
 		return self.value.get(k,default)
+
+class ReadOnlyDictData(DictData):
+	def __setitem__(self,k,v):
+		raise ReadOnlyError("Cannot set item {} to {}".format(k,v))
+
+class Numerical(ReadOnlyDictData):
+	def load(self,filename):
+		super(Numerical,self).load(filename)
+		n = {}
+		for k in self.value:
+			n[int(k)]=self.value[k]
+		self.value = n