<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def walk(cls, top=".", ext=".abo"):
 """ 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. """

        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