Add optional 'onerror' argument to os.walk(), to control error

handling.

Lib/os.py

@@ -203,7 +203,7 @@ def renames(old, new):
 
 __all__.extend(["makedirs", "removedirs", "renames"])
 
-def walk(top, topdown=True):
+def walk(top, topdown=True, onerror=None):
     """Directory tree generator.
 
     For each directory in the directory tree rooted at top (including top
@@ -232,6 +232,13 @@ def walk(top, topdown=True):
     dirnames have already been generated by the time dirnames itself is
     generated.
 
+    By default errors from the os.listdir() call are ignored.  If
+    optional arg 'onerror' is specified, it should be a function; it
+    will be called with one argument, an os.error instance.  It can
+    report the error to continue with the walk, or raise the exception
+    to abort the walk.  Note that the filename is available as the
+    filename attribute of the exception object.
+
     Caution:  if you pass a relative pathname for top, don't change the
     current working directory between resumptions of walk.  walk never
     changes the current directory, and assumes that the client doesn't
@@ -259,7 +266,9 @@ def walk(top, topdown=True):
         # Note that listdir and error are globals in this module due
         # to earlier import-*.
         names = listdir(top)
-    except error:
+    except error, err:
+        if onerror is not None:
+            onerror(err)
         return
 
     dirs, nondirs = [], []
@@ -274,7 +283,7 @@ def walk(top, topdown=True):
     for name in dirs:
         path = join(top, name)
         if not islink(path):
-            for x in walk(path, topdown):
+            for x in walk(path, topdown, onerror):
                 yield x
     if not topdown:
         yield top, dirs, nondirs