diff --git a/calendar/teachingdates/calendars/basecalendar.py b/calendar/teachingdates/calendars/basecalendar.py
index 4f219c7..c66e9c0 100644
--- a/calendar/teachingdates/calendars/basecalendar.py
+++ b/calendar/teachingdates/calendars/basecalendar.py
@@ -16,7 +16,8 @@
     lecture_offsets = []
     skipped_lectures = []
     mondays = []
-    period = "iso"
+    period = None
+    paper = None
     year = datetime.date.today().year
 
     def __init__(self,