--- a/mercurial/match.py	Sat May 06 04:51:25 2017 +0530
+++ b/mercurial/match.py	Fri Feb 10 16:56:29 2017 -0800
@@ -236,7 +236,7 @@
 
     @propertycache
     def _dirs(self):
-        return set(util.dirs(self._fileroots)) | set(['.'])
+        return set(util.dirs(self._fileroots)) | {'.'}
 
     def visitdir(self, dir):
         '''Decides whether a directory should be visited based on whether it