Be more informative when unable to JSON serialize

elasticsearch/serializer.py

@@ -28,7 +28,7 @@ class JSONSerializer(object):
             return data.isoformat()
         elif isinstance(data, Decimal):
             return float(data)
-        raise TypeError
+        raise TypeError("Unable to serialize %r (type: %s)" % (data, type(data)))
 
     def loads(self, s):
         try: