about directories the caller creates or renames before it resumes
\function{walk()} again. Modifying \var{dirnames} when \var{topdown} is
false is ineffective, because in bottom-up mode the directories in
-\var{dirnames} are generated before \var{dirnames} itself is generated.
+\var{dirnames} are generated before \var{dirpath} itself is generated.
By default errors from the \code{os.listdir()} call are ignored. If
optional argument \var{onerror} is specified, it should be a function;