Reorder env variable checks

Author: pablogsal

Lib/test/test_traceback.py

@@ -4314,8 +4314,8 @@ def foo():
         self.assertEqual(actual, expected)
 
     def test_colorized_detection_checks_for_environment_variables(self):
-        with unittest.mock.patch("sys.stderr") as stderr_mock:
-            stderr_mock.isatty.return_value = True
+        with unittest.mock.patch("os.isatty") as isatty_mock:
+            isatty_mock.return_value = True
             with unittest.mock.patch("os.environ", {'TERM': 'dumb'}):
                 self.assertEqual(traceback._can_colorize(), False)
             with unittest.mock.patch("os.environ", {'PY_COLORS': '1'}):
@@ -4325,12 +4325,12 @@ def test_colorized_detection_checks_for_environment_variables(self):
             with unittest.mock.patch("os.environ", {'NO_COLOR': '1'}):
                 self.assertEqual(traceback._can_colorize(), False)
             with unittest.mock.patch("os.environ", {'NO_COLOR': '1', "PY_COLORS": '1'}):
-                self.assertEqual(traceback._can_colorize(), True)
+                self.assertEqual(traceback._can_colorize(), False)
             with unittest.mock.patch("os.environ", {'FORCE_COLOR': '1'}):
                 self.assertEqual(traceback._can_colorize(), True)
             with unittest.mock.patch("os.environ", {'FORCE_COLOR': '1', 'NO_COLOR': '1'}):
                 self.assertEqual(traceback._can_colorize(), False)
-            stderr_mock.isatty.return_value = False
+            isatty_mock.return_value = False
             self.assertEqual(traceback._can_colorize(), False)
 
 if __name__ == "__main__":

Lib/traceback.py

@@ -1,6 +1,7 @@
 """Extract, format and print information about Python stack traces."""
 
 import os
+import io
 import collections.abc
 import itertools
 import linecache
@@ -141,19 +142,22 @@ def _can_colorize():
         except (ImportError, AttributeError):
             return False
 
-    if not _COLORIZE:
+    if "NO_COLOR" in os.environ:
         return False
-    if os.environ.get("PY_COLORS") == "1":
-        return True
     if os.environ.get("PY_COLORS") == "0":
         return False
-    if "NO_COLOR" in os.environ:
+    if not _COLORIZE:
         return False
     if "FORCE_COLOR" in os.environ:
         return True
-    return (
-        hasattr(sys.stderr, "isatty") and sys.stderr.isatty() and os.environ.get("TERM") != "dumb"
-    )
+    if os.environ.get("PY_COLORS") == "1":
+        return True
+    if os.environ.get("TERM") == "dumb":
+        return False
+    try:
+        return os.isatty(sys.stderr.fileno())
+    except io.UnsupportedOperation:
+        return sys.stderr.isatty()
 
 def _print_exception_bltin(exc, /):
     file = sys.stderr if sys.stderr is not None else sys.__stderr__