How to use the thefuck.logs.warn function in thefuck

def shell_logger(output):
    """Logs shell output to the `output`.

    Works like unix script command with `-f` flag.

    """
    if not os.environ.get('SHELL'):
        logs.warn("Shell logger doesn't support your platform.")
        sys.exit(1)

    fd = os.open(output, os.O_CREAT | os.O_TRUNC | os.O_RDWR)
    os.write(fd, b'\x00' * const.LOG_SIZE_IN_BYTES)
    buffer = mmap.mmap(fd, const.LOG_SIZE_IN_BYTES, mmap.MAP_SHARED, mmap.PROT_WRITE)
    return_code = _spawn(os.environ['SHELL'], partial(_read, buffer))

    sys.exit(return_code)

parser.print_help()
    elif known_args.version:
        logs.version(get_installation_info().version,
                     sys.version.split()[0], shell.info())
    # It's important to check if an alias is being requested before checking if
    # `TF_HISTORY` is in `os.environ`, otherwise it might mess with subshells.
    # Check https://github.com/nvbn/thefuck/issues/921 for reference
    elif known_args.alias:
        print_alias(known_args)
    elif known_args.command or 'TF_HISTORY' in os.environ:
        fix_command(known_args)
    elif known_args.shell_logger:
        try:
            from .shell_logger import shell_logger  # noqa: E402
        except ImportError:
            logs.warn('Shell logger supports only Linux and macOS')
        else:
            shell_logger(known_args.shell_logger)
    else:
        parser.print_usage()

def get_output(script):
    """Gets command output from shell logger."""
    with logs.debug_time(u'Read output from external shell logger'):
        commands = _get_last_n(const.SHELL_LOGGER_LIMIT)
        for command in commands:
            if command['command'] == script:
                lines = _get_output_lines(command['output'])
                output = '\n'.join(lines).strip()
                return output
            else:
                logs.warn("Output isn't available in shell logger")
                return None

def get_output(script):
    """Reads script output from log.

    :type script: str
    :rtype: str | None

    """
    if six.PY2:
        logs.warn('Experimental instant mode is Python 3+ only')
        return None

    if 'THEFUCK_OUTPUT_LOG' not in os.environ:
        logs.warn("Output log isn't specified")
        return None

    if const.USER_COMMAND_MARK not in os.environ.get('PS1', ''):
        logs.warn(
            "PS1 doesn't contain user command mark, please ensure "
            "that PS1 is not changed after The Fuck alias initialization")
        return None

    try:
        with logs.debug_time(u'Read output from log'):
            fd = os.open(os.environ['THEFUCK_OUTPUT_LOG'], os.O_RDONLY)
            buffer = mmap.mmap(fd, const.LOG_SIZE_IN_BYTES, mmap.MAP_SHARED, mmap.PROT_READ)

def get_output(script):
    """Reads script output from log.

    :type script: str
    :rtype: str | None

    """
    if six.PY2:
        logs.warn('Experimental instant mode is Python 3+ only')
        return None

    if 'THEFUCK_OUTPUT_LOG' not in os.environ:
        logs.warn("Output log isn't specified")
        return None

    if const.USER_COMMAND_MARK not in os.environ.get('PS1', ''):
        logs.warn(
            "PS1 doesn't contain user command mark, please ensure "
            "that PS1 is not changed after The Fuck alias initialization")
        return None

    try:
        with logs.debug_time(u'Read output from log'):
            fd = os.open(os.environ['THEFUCK_OUTPUT_LOG'], os.O_RDONLY)
            buffer = mmap.mmap(fd, const.LOG_SIZE_IN_BYTES, mmap.MAP_SHARED, mmap.PROT_READ)
            _skip_old_lines(buffer)
            lines = _get_output_lines(script, buffer)
            output = '\n'.join(lines).strip()
            logs.debug(u'Received output: {}'.format(output))

def _get_alias(known_args):
    if six.PY2:
        warn("The Fuck will drop Python 2 support soon, more details "
             "https://github.com/nvbn/thefuck/issues/685")

    alias = shell.app_alias(known_args.alias)

    if known_args.enable_experimental_instant_mode:
        if six.PY2:
            warn("Instant mode requires Python 3")
        elif not which('script'):
            warn("Instant mode requires `script` app")
        else:
            return shell.instant_mode_alias(known_args.alias)

    return alias

def _get_alias(known_args):
    if six.PY2:
        warn("The Fuck will drop Python 2 support soon, more details "
             "https://github.com/nvbn/thefuck/issues/685")

    alias = shell.app_alias(known_args.alias)

    if known_args.enable_experimental_instant_mode:
        if six.PY2:
            warn("Instant mode requires Python 3")
        elif not which('script'):
            warn("Instant mode requires `script` app")
        else:
            return shell.instant_mode_alias(known_args.alias)

    return alias

def _setup_db(self):
        cache_dir = self._get_cache_dir()
        cache_path = Path(cache_dir).joinpath('thefuck').as_posix()

        try:
            self._db = shelve.open(cache_path)
        except shelve_open_error + (ImportError,):
            # Caused when switching between Python versions
            warn("Removing possibly out-dated cache")
            os.remove(cache_path)
            self._db = shelve.open(cache_path)

        atexit.register(self._db.close)