--- a/hgext/evolve.py	Wed Apr 20 18:58:52 2016 +0000
+++ b/hgext/evolve.py	Wed Apr 20 18:59:46 2016 +0000
@@ -3938,7 +3938,7 @@
 def _evolvestateread(repo):
     try:
         f = repo.vfs('evolvestate')
-    except IOError, err:
+    except IOError as err:
         if err.errno != errno.ENOENT:
             raise
         return None