parameters: (pathname)
docstring: Return a pair of the subdirectory names and filenames immediately
      contained within the 'pathname' directory.
  
      If 'pathname' does not exist, then None is returned.
docstring_summary: Return a pair of the subdirectory names and filenames immediately
      contained within the 'pathname' directory.
docstring_tokens: Return a pair of the subdirectory names and filenames immediately contained within the pathname directory .
function: def _list_dir(pathname):
      """
      Return a pair of the subdirectory names and filenames immediately
      contained within the 'pathname' directory.
  
      If 'pathname' does not exist, then None is returned.
      """
  
      try:
          (_root, dirs, files) = os.walk(pathname).next()
          return (dirs, files)
      except StopIteration:
          return None
function_tokens: def _list_dir ( pathname ) : try : ( _root , dirs , files ) = os . walk ( pathname ) . next ( ) return ( dirs , files ) except StopIteration : return None