diff -r ad56204f733e -r 5564fcd031df mercurial/hook.py
--- a/mercurial/hook.py	Tue Nov 08 22:22:22 2016 +0900
+++ b/mercurial/hook.py	Tue Nov 08 22:41:45 2016 +0900
@@ -209,11 +209,11 @@
         for hname, cmd in hooks:
             if oldstdout == -1 and _redirect:
                 try:
-                    stdoutno = sys.__stdout__.fileno()
-                    stderrno = sys.__stderr__.fileno()
+                    stdoutno = sys.stdout.fileno()
+                    stderrno = sys.stderr.fileno()
                     # temporarily redirect stdout to stderr, if possible
                     if stdoutno >= 0 and stderrno >= 0:
-                        sys.__stdout__.flush()
+                        sys.stdout.flush()
                         oldstdout = os.dup(stdoutno)
                         os.dup2(stderrno, stdoutno)
                 except (OSError, AttributeError):
@@ -258,7 +258,7 @@
             sys.stderr.flush()
     finally:
         if _redirect and oldstdout >= 0:
-            sys.__stdout__.flush()  # write hook output to stderr fd
+            sys.stdout.flush()  # write hook output to stderr fd
             os.dup2(oldstdout, stdoutno)
             os.close(oldstdout)