<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def info_file(distro=None):
 """Return default distroinfo info file"""

    if not distro:
        distro = cfg['DISTRO']
    info_file_conf = distro.upper() + 'INFO_FILE'
    try:
        return cfg[info_file_conf]
    except KeyError:
        raise exception.InvalidUsage(
            why="Couldn't find config option %s for distro: %s"
                % (info_file_conf, distro))