1 files changed, 14 insertions, 4 deletions
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index c587b68b89..c342bbcf19 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -258,10 +258,20 @@ def ismount(path):
 # or to impose a different order of visiting.
 
 def walk(top, func, arg):
-    """walk(top,func,arg) calls func(arg, d, files) for each directory "d"
-    in the tree  rooted at "top" (including "top" itself).  "files" is a list
-    of all the files and subdirs in directory "d".
-    """
+    """Directory tree walk with callback function.
+
+    For each directory in the directory tree rooted at top (including top
+    itself, but excluding '.' and '..'), call func(arg, dirname, fnames).
+    dirname is the name of the directory, and fnames a list of the names of
+    the files and subdirectories in dirname (excluding '.' and '..').  func
+    may modify the fnames list in-place (e.g. via del or slice assignment),
+    and walk will only recurse into the subdirectories whose names remain in
+    fnames; this can be used to implement a filter, or to impose a specific
+    order of visiting.  No semantics are defined for, or required of, arg,
+    beyond that arg is always passed to func.  It can be used, e.g., to pass
+    a filename pattern, or a mutable object designed to accumulate
+    statistics.  Passing None for arg is common."""
+
     try:
         names = os.listdir(top)
     except os.error: