# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1508882959 -7200
# Node ID f8b6e1ae40f429d568c2967b372942842971a5e9
# Parent  aa6e36ed60eb17cc212e6e22439399c75b454581
Employ a simple filter invocation to materialise recurrence periods and to
filter exception periods.

diff -r aa6e36ed60eb -r f8b6e1ae40f4 imiptools/data.py
--- a/imiptools/data.py	Tue Oct 24 23:24:41 2017 +0200
+++ b/imiptools/data.py	Wed Oct 25 00:09:19 2017 +0200
@@ -1278,19 +1278,13 @@
 
     # Return a sorted list of the periods.
 
-    periods = list(MergingIterator([rule_periods, iter(rdates or [])]))
+    periods = MergingIterator([rule_periods, iter(rdates or [])])
 
     # Exclude exception dates.
 
-    exdates = obj.get_date_value_item_periods("EXDATE", obj_tzid or tzid)
+    exdates = set(obj.get_date_value_item_periods("EXDATE", obj_tzid or tzid) or [])
 
-    if exdates:
-        for period in exdates:
-            i = bisect_left(periods, period)
-            while i < len(periods) and periods[i] == period:
-                del periods[i]
-
-    return periods
+    return filter(lambda p, excluded=exdates: p not in excluded, periods)
 
 def get_sender_identities(mapping):