bpo-30125: disable faulthandler in ctypes test_SEH

Disable faulthandler to run test_SEH() of test_ctypes to prevent the following log with a traceback: Windows fatal exception: access violation Add support.disable_faulthandler() context manager.
python · vstinner · Apr 21, 2017 · Apr 21, 2017 · Apr 21, 2017 · 25cef3e489d1dd0883d121e5b27d7850fc1e21e1
commit 25cef3e489d1dd0883d121e5b27d7850fc1e21e1
diff --git a/Lib/ctypes/test/test_win32.py b/Lib/ctypes/test/test_win32.py
@@ -41,15 +41,19 @@ class FunctionCallTestCase(unittest.TestCase):
    @unittest.skipIf(sys.executable.lower().endswith('_d.exe'),
                     "SEH not enabled in debug builds")
    def test_SEH(self):
-        # Call functions with invalid arguments, and make sure
-        # that access violations are trapped and raise an
-        # exception.
-        self.assertRaises(OSError, windll.kernel32.GetModuleHandleA, 32)
+        # Disable faulthandler to prevent logging the warning:
+        # "Windows fatal exception: access violation"
+        with support.disable_faulthandler():
+            # Call functions with invalid arguments, and make sure
+            # that access violations are trapped and raise an
+            # exception.
+            self.assertRaises(OSError, windll.kernel32.GetModuleHandleA, 32)

    def test_noargs(self):
        # This is a special case on win32 x64
        windll.user32.GetDesktopWindow()

+
 @unittest.skipUnless(sys.platform == "win32", 'Windows-specific test')
 class TestWintypes(unittest.TestCase):
    def test_HWND(self):

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
@@ -2595,3 +2595,19 @@ def setswitchinterval(interval):
        if _is_android_emulator:
            interval = minimum_interval
    return sys.setswitchinterval(interval)
+
+
+@contextlib.contextmanager
+def disable_faulthandler():
+    # use sys.__stderr__ instead of sys.stderr, since regrtest replaces
+    # sys.stderr with a StringIO which has no file descriptor when a test
+    # is run with -W/--verbose3.
+    fd = sys.__stderr__.fileno()
+
+    is_enabled = faulthandler.is_enabled()
+    try:
+        faulthandler.disable()
+        yield
+    finally:
+        if is_enabled:
+            faulthandler.enable(file=fd, all_threads=True)