diff -r 2959c3e986e0 -r bd872f64a8ba mercurial/__init__.py
--- a/mercurial/__init__.py	Sat May 06 04:51:25 2017 +0530
+++ b/mercurial/__init__.py	Fri Feb 10 16:56:29 2017 -0800
@@ -22,14 +22,14 @@
 
 # Modules that have both Python and C implementations. See also the
 # set of .py files under mercurial/pure/.
-_dualmodules = set([
+_dualmodules = {
     'mercurial.base85',
     'mercurial.bdiff',
     'mercurial.diffhelpers',
     'mercurial.mpatch',
     'mercurial.osutil',
     'mercurial.parsers',
-])
+}
 
 class hgimporter(object):
     """Object that conforms to import hook interface defined in PEP-302."""