Guarantee that /usr/local/bin and /usr/bin are in PATH

def _get_path():
    """Guarantee that /usr/local/bin and /usr/bin are in PATH"""
    if _path:
        return _path[0]
    environ_paths = set(os.environ['PATH'].split(':'))
    environ_paths.add('/usr/local/bin')
    environ_paths.add('/usr/bin')
    _path.append(':'.join(environ_paths))
    logger.debug('PATH = %s', _path[-1])
    return _path[0]