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

@@ -373,61 +373,45 @@ 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)
+ 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()
+ else:
+ is_dir = entry.is_dir()
+ except OSError:
+ # If is_dir() raises an OSError, consider the entry not to
+ # be a directory, same behaviour as os.path.isdir().
+ is_dir = False
+
+ if is_dir:
+ dirs.append(entry.name)
+ else:
+ nondirs.append(entry.name)
+
+ if not topdown and is_dir:
+ # Bottom-up: traverse into sub-directory, but exclude
+ # symlinks to directories if followlinks is False
+ if followlinks:
+ walk_into = True
+ else:
+ try:
+ is_symlink = entry.is_symlink()
+ except OSError:
+ # If is_symlink() raises an OSError, consider the
+ # entry not to be a symbolic link, same behaviour
+ # as os.path.islink().
+ is_symlink = False
+ walk_into = not is_symlink
+
+ if walk_into:
+ walk_dirs.append(entry.path)
  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
-
- try:
- if followlinks is _walk_symlinks_as_files:
- is_dir = entry.is_dir(follow_symlinks=False) and not entry.is_junction()
- else:
- is_dir = entry.is_dir()
- except OSError:
- # If is_dir() raises an OSError, consider the entry not to
- # be a directory, same behaviour as os.path.isdir().
- is_dir = False
-
- if is_dir:
- dirs.append(entry.name)
- else:
- nondirs.append(entry.name)
-
- if not topdown and is_dir:
- # Bottom-up: traverse into sub-directory, but exclude
- # symlinks to directories if followlinks is False
- if followlinks:
- walk_into = True
- else:
- try:
- is_symlink = entry.is_symlink()
- except OSError:
- # If is_symlink() raises an OSError, consider the
- # entry not to be a symbolic link, same behaviour
- # as os.path.islink().
- is_symlink = False
- walk_into = not is_symlink
-
- if walk_into:
- walk_dirs.append(entry.path)
- if cont:
- continue
-
  if topdown:
  # Yield before sub-directory traversal if going top down
  yield top, dirs, nondirs

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.