code: def walk(cls, top=".", ext=".abo"):
          
          paths = []
          for root, dirs, files in os.walk(top):
              for f in files:
                  if f.endswith(ext):
                      paths.append(os.path.join(root, f))
  
          parser = cls()
          okfiles = parser.parse(paths)
          return parser, paths, okfiles
docs: Scan directory tree starting from top, look for files with extension `ext` and
          parse timing data.
  
          Return: (parser, paths, okfiles)
              where `parser` is the new object, `paths` is the list of files found and `okfiles`
              is the list of files that have been parsed successfully.
              (okfiles == paths) if all files have been parsed.