diff -r 2959c3e986e0 -r bd872f64a8ba mercurial/revlog.py
--- a/mercurial/revlog.py	Sat May 06 04:51:25 2017 +0530
+++ b/mercurial/revlog.py	Fri Feb 10 16:56:29 2017 -0800
@@ -913,8 +913,8 @@
             stop = []
         stoprevs = set([self.rev(n) for n in stop])
         startrev = self.rev(start)
-        reachable = set((startrev,))
-        heads = set((startrev,))
+        reachable = {startrev}
+        heads = {startrev}
 
         parentrevs = self.parentrevs
         for r in self.revs(start=startrev + 1):
@@ -2039,7 +2039,7 @@
     DELTAREUSESAMEREVS = 'samerevs'
     DELTAREUSENEVER = 'never'
 
-    DELTAREUSEALL = set(['always', 'samerevs', 'never'])
+    DELTAREUSEALL = {'always', 'samerevs', 'never'}
 
     def clone(self, tr, destrevlog, addrevisioncb=None,
               deltareuse=DELTAREUSESAMEREVS, aggressivemergedeltas=None):