Default to stdout isatty for colour detection instead of stderr

Lib/_colorize.py

@@ -49,7 +49,7 @@ def can_colorize() -> bool:
         if os.environ.get("TERM") == "dumb":
             return False
 
-    if not hasattr(sys.stderr, "fileno"):
+    if not hasattr(sys.stdout, "fileno"):
         return False
 
     if sys.platform == "win32":
@@ -62,6 +62,6 @@ def can_colorize() -> bool:
             return False
 
     try:
-        return os.isatty(sys.stderr.fileno())
+        return os.isatty(sys.stdout.fileno())
     except io.UnsupportedOperation:
-        return sys.stderr.isatty()
+        return sys.stdout.isatty()

Lib/test/test_code_module.py

@@ -5,8 +5,7 @@
 from textwrap import dedent
 from contextlib import ExitStack
 from unittest import mock
-from test.support import import_helper
-
+from test.support import force_not_colorized_test_class, import_helper
 
 code = import_helper.import_module('code')
 
@@ -30,6 +29,7 @@ def mock_sys(self):
         del self.sysmod.ps2
 
 
+@force_not_colorized_test_class
 class TestInteractiveConsole(unittest.TestCase, MockSys):
     maxDiff = None
 

Lib/test/test_traceback.py

@@ -21,7 +21,7 @@
 from test.support.os_helper import TESTFN, unlink
 from test.support.script_helper import assert_python_ok, assert_python_failure
 from test.support.import_helper import forget
-from test.support import force_not_colorized
+from test.support import force_not_colorized, force_not_colorized_test_class
 
 import json
 import textwrap
@@ -1712,6 +1712,7 @@ def f():
 
 
 @requires_debug_ranges()
+@force_not_colorized_test_class
 class PurePythonTracebackErrorCaretTests(
     PurePythonExceptionFormattingMixin,
     TracebackErrorLocationCaretTestBase,
@@ -1725,6 +1726,7 @@ class PurePythonTracebackErrorCaretTests(
 
 @cpython_only
 @requires_debug_ranges()
+@force_not_colorized_test_class
 class CPythonTracebackErrorCaretTests(
     CAPIExceptionFormattingMixin,
     TracebackErrorLocationCaretTestBase,
@@ -1736,6 +1738,7 @@ class CPythonTracebackErrorCaretTests(
 
 @cpython_only
 @requires_debug_ranges()
+@force_not_colorized_test_class
 class CPythonTracebackLegacyErrorCaretTests(
     CAPIExceptionFormattingLegacyMixin,
     TracebackErrorLocationCaretTestBase,
@@ -2149,10 +2152,12 @@ def test_print_exception_bad_type_python(self):
 boundaries = re.compile(
     '(%s|%s)' % (re.escape(cause_message), re.escape(context_message)))
 
+@force_not_colorized_test_class
 class TestTracebackFormat(unittest.TestCase, TracebackFormatMixin):
     pass
 
 @cpython_only
+@force_not_colorized_test_class
 class TestFallbackTracebackFormat(unittest.TestCase, TracebackFormatMixin):
     DEBUG_RANGES = False
     def setUp(self) -> None:
@@ -2940,6 +2945,7 @@ def f():
         self.assertEqual(report, expected)
 
 
+@force_not_colorized_test_class
 class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
     #
     # This checks reporting through the 'traceback' module, with both
@@ -2956,6 +2962,7 @@ def get_report(self, e):
         return s
 
 
+@force_not_colorized_test_class
 class CExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
     #
     # This checks built-in reporting by the interpreter.