bpo-42053: fixed fwalk incorrect boolean test for non-fd arguments

Lib/os.py

@@ -461,7 +461,7 @@ def fwalk(top=".", topdown=True, onerror=None, *, follow_symlinks=False, dir_fd=
                 dirs.remove('CVS')  # don't visit CVS directories
         """
         sys.audit("os.fwalk", top, topdown, onerror, follow_symlinks, dir_fd)
-        if not isinstance(top, int) or not hasattr(top, '__index__'):
+        if not isinstance(top, int) and not hasattr(top, '__index__'):
             top = fspath(top)
         # Note: To guard against symlink races, we use the standard
         # lstat()/open()/fstat() trick.

Lib/test/test_os.py

@@ -1527,6 +1527,25 @@ def test_fd_leak(self):
         self.addCleanup(os.close, newfd)
         self.assertEqual(newfd, minfd)
 
+    def test_fwalk(self):
+        class CustomBaseClass():
+            def __init__(self, val):
+                self.val = val
+            def __index__(self):
+                return os.open(self.val, os.O_RDONLY)
+        class CustomStrClass(CustomBaseClass):
+            def __fspath__(self):
+                return str(self.val)
+
+        top = CustomBaseClass('.')
+        with self.assertRaisesRegex(TypeError, f'open: path should be string, bytes or os.PathLike'):
+            next(os.fwalk(top=top, follow_symlinks=True))
+
+        top = CustomStrClass('.')
+        root, dirs, files, rootfd  = next(os.fwalk(top=top, follow_symlinks=True))
+        self.assertIsInstance(root, CustomStrClass)
+        self.assertNotIsInstance(root, str)
+
     # fwalk() keeps file descriptors open
     test_walk_many_open_files = None
 

Misc/NEWS.d/next/Library/2021-08-04-16-45-58.bpo-42053.WzOl39.rst

@@ -0,0 +1,2 @@
+fixed incorrect boolean test for non-fd arguments in os.fwalk.
+Added test with custom class and __index__ method