bpo-45410: regrtest -W leaves stdout/err FD unchanged (GH-28915)

support.print_warning() now stores the original value of
sys.__stderr__ and uses it to log warnings. libregrtest uses the same
stream to log unraisable exceptions and uncaught threading
exceptions.

Partially revert commit dbe213de7ef28712bbfdb9d94a33abb9c33ef0c2:
libregrtest no longer replaces sys.__stdout__, sys.__stderr__, and
stdout and stderr file descriptors.

Remove also a few unused imports in libregrtest.

1 files changed, 2 insertions, 12 deletions

diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index 8b55352..d5a1d44 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -469,12 +469,8 @@ class TestSupport(unittest.TestCase):
                 if time.monotonic() > deadline:
                     self.fail("timeout")
 
-                old_stderr = sys.__stderr__
-                try:
-                    sys.__stderr__ = stderr
+                with support.swap_attr(support.print_warning, 'orig_stderr', stderr):
                     support.reap_children()
-                finally:
-                    sys.__stderr__ = old_stderr
 
                 # Use environment_altered to check if reap_children() found
                 # the child process
@@ -674,14 +670,8 @@ class TestSupport(unittest.TestCase):
 
     def check_print_warning(self, msg, expected):
         stderr = io.StringIO()
-
-        old_stderr = sys.__stderr__
-        try:
-            sys.__stderr__ = stderr
+        with support.swap_attr(support.print_warning, 'orig_stderr', stderr):
             support.print_warning(msg)
-        finally:
-            sys.__stderr__ = old_stderr
-
         self.assertEqual(stderr.getvalue(), expected)
 
     def test_print_warning(self):