# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1421953986 -3600
# Node ID 3feba2b55cfcf838e76934238996764f20e2f890
# Parent  1fe444f390cd9e5558420c901ef002517fa8c214
Added some explanatory comments.

diff -r 1fe444f390cd -r 3feba2b55cfc imiptools/period.py
--- a/imiptools/period.py	Thu Jan 22 18:41:32 2015 +0100
+++ b/imiptools/period.py	Thu Jan 22 20:13:06 2015 +0100
@@ -148,11 +148,15 @@
     for point, (starting, ending) in get_scale(l):
 
         # Discard all active events ending at or before this start time.
+        # Free up the position in the active list.
 
         for t in ending:
             i = active.index(t)
             active[i] = None
 
+        # For each event starting at the current point, fill any newly-vacated
+        # position or add to the end of the active list.
+
         for t in starting:
             try:
                 i = active.index(None)
@@ -160,6 +164,8 @@
             except ValueError:
                 active.append(t)
 
+        # Discard vacant positions from the end of the active list.
+
         while active and active[-1] is None:
             active.pop()