diff -r d8e49a2795e7 Lib/os.py
--- a/Lib/os.py	Sat Mar 07 18:14:07 2015 -0800
+++ b/Lib/os.py	Sat Mar 07 22:10:20 2015 -0500
@@ -323,7 +323,7 @@
     the value of topdown, the list of subdirectories is retrieved before the
     tuples for the directory and its subdirectories are generated.
 
-    By default errors from the os.listdir() call are ignored.  If
+    By default errors from the os.scandir() call are ignored.  If
     optional arg 'onerror' is specified, it should be a function; it
     will be called with one argument, an OSError instance.  It can
     report the error to continue with the walk, or raise the exception
@@ -351,36 +351,43 @@
             dirs.remove('CVS')  # don't visit CVS directories
 
     """
-
-    islink, join, isdir = path.islink, path.join, path.isdir
-
-    # We may not have read permission for top, in which case we can't
-    # get a list of the files the directory contains.  os.walk
-    # always suppressed the exception then, rather than blow up for a
-    # minor reason when (say) a thousand readable directories are still
-    # left to visit.  That logic is copied here.
+    # Determine which are files and which are directories
+    dirs = []
+    nondirs = []
+    symlinks = set()
     try:
-        # Note that listdir is global in this module due
-        # to earlier import-*.
-        names = listdir(top)
-    except OSError as err:
+        for entry in scandir(top):
+            try:
+                if entry.is_dir():
+                    dirs.append(entry.name)
+                else:
+                    nondirs.append(entry.name)
+            except OSError:
+                # os.walk() includes paths where is_dir() raises
+                # OSError in the nondirs list
+                nondirs.append(entry.name)
+            try:
+                if entry.is_symlink():
+                    symlinks.add(entry.name)
+            except OSError:
+                pass
+    except OSError as error:
         if onerror is not None:
-            onerror(err)
+            onerror(error)
         return
 
-    dirs, nondirs = [], []
-    for name in names:
-        if isdir(join(top, name)):
-            dirs.append(name)
-        else:
-            nondirs.append(name)
-
+    # Yield before recursion if going top down
     if topdown:
         yield top, dirs, nondirs
+
+    # Recurse into sub-directories, following symbolic links if
+    # "followlinks" is True
     for name in dirs:
-        new_path = join(top, name)
-        if followlinks or not islink(new_path):
+        if followlinks or name not in symlinks:
+            new_path = path.join(top, name)
             yield from walk(new_path, topdown, onerror, followlinks)
+
+    # Yield after recursion if going bottom up
     if not topdown:
         yield top, dirs, nondirs