def retrieve_taf(station_icao) -> typing.Tuple[typing.Union[str, None], typing.Union[str, None]]:
url = _BASE_TAF_URL.format(station=station_icao)<EOL>with requests.get(url) as resp:<EOL><INDENT>if not resp.ok:<EOL><INDENT>return f'<STR_LIT>'f'<STR_LIT>'f'<STR_LIT>', None<EOL><DEDENT>return None, resp.content.decode().split('<STR_LIT:\n>')[<NUM_LIT:1>]<EOL><DEDENT>
Retrieves a TAF string from an online database

Args:
    station_icao: ICAO of the station

Returns:
    tuple of error, metar_str