gh-47169: Adding errno Symbolic Values to OSError.__str__()

Lib/test/test_exceptions.py

@@ -410,7 +410,7 @@ def test_WindowsError(self):
             w = OSError(9, 'foo', 'bar')
             self.assertEqual(w.errno, 9)
             self.assertEqual(w.winerror, None)
-            self.assertEqual(str(w), "[Errno 9] foo: 'bar'")
+            self.assertEqual(str(w), "[Errno 9 (EBADF)] foo: 'bar'")
             # ERROR_PATH_NOT_FOUND (win error 3) becomes ENOENT (2)
             w = OSError(0, 'foo', 'bar', 3)
             self.assertEqual(w.errno, 2)
@@ -1837,6 +1837,16 @@ def g():
                 next(i)
                 next(i)
 
+    def test_OSError_errno_error_message(self):
+        # From PR 14988.
+        with self.assertRaises(OSError) as cm:
+            open('__non-existent__')
+        self.assertEqual(
+            str(cm.exception),
+            f"[Errno {errno.ENOENT} (ENOENT)] "
+            "No such file or directory: '__non-existent__'",
+        )
+
     @unittest.skipUnless(__debug__, "Won't work if __debug__ is False")
     def test_assert_shadowing(self):
         # Shadowing AssertionError would cause the assert statement to

Lib/test/test_signal.py

@@ -384,7 +384,8 @@ def handler(signum, frame):
             if ('Exception ignored while trying to write to the signal wakeup fd'
                 not in err):
                 raise AssertionError(err)
-            if ('OSError: [Errno %d]' % errno.EBADF) not in err:
+            if ('OSError: [Errno %d (%s)]' %
+                (errno.EBADF, errno.errorcode[errno.EBADF])) not in err:
                 raise AssertionError(err)
         else:
             raise AssertionError("ZeroDivisionError not raised")

Lib/test/test_tabnanny.py

@@ -238,7 +238,7 @@ def test_when_nannynag_error(self):
     def test_when_no_file(self):
         """A python file which does not exist actually in system."""
         path = 'no_file.py'
-        err = (f"{path!r}: I/O Error: [Errno {errno.ENOENT}] "
+        err = (f"{path!r}: I/O Error: [Errno {errno.ENOENT} (ENOENT)] "
               f"{os.strerror(errno.ENOENT)}: {path!r}\n")
         with self.assertRaises(SystemExit):
             self.verify_tabnanny_check(path, err=err)

Misc/NEWS.d/next/Core_and_Builtins/2026-05-18-16-20-18.gh-issue-47169.kE86QZ.rst

@@ -0,0 +1 @@
+Include the symbolic error name in :exc:`OSError` exception string representations.