GH-119169: Simplify os.walk() exception handling (#121435)

Handle errors from `os.scandir()` and `ScandirIterator` similarly, which
lets us loop over directory entries with `for`.

Lib/os.py

@@ -373,26 +373,8 @@ def walk(top, topdown=True, onerror=None, followlinks=False):
         # minor reason when (say) a thousand readable directories are still
         # left to visit.
         try:
-            scandir_it = scandir(top)
-        except OSError as error:
-            if onerror is not None:
-                onerror(error)
-            continue
-
-        cont = False
-        with scandir_it:
-            while True:
-                try:
-                    try:
-                        entry = next(scandir_it)
-                    except StopIteration:
-                        break
-                except OSError as error:
-                    if onerror is not None:
-                        onerror(error)
-                    cont = True
-                    break
-
+            with scandir(top) as entries:
+                for entry in entries:
                     try:
                         if followlinks is _walk_symlinks_as_files:
                             is_dir = entry.is_dir(follow_symlinks=False) and not entry.is_junction()
@@ -425,7 +407,9 @@ def walk(top, topdown=True, onerror=None, followlinks=False):
 
                         if walk_into:
                             walk_dirs.append(entry.path)
-        if cont:
+        except OSError as error:
+            if onerror is not None:
+                onerror(error)
             continue
 
         if topdown:

Misc/NEWS.d/next/Library/2024-07-06-16-08-39.gh-issue-119169.o0YymL.rst

@@ -0,0 +1 @@
+Slightly speed up :func:`os.walk` by simplifying exception handling.