def _list_variables(self, station_codes):
<EOL>rvar = re.compile(r"<STR_LIT>")<EOL>variables = set()<EOL>resp = requests.post(<EOL>self.obs_retrieval_url,<EOL>data={<EOL>"<STR_LIT:state>": "<STR_LIT>",<EOL>"<STR_LIT>": "<STR_LIT>",<EOL>"<STR_LIT>": "<STR_LIT:3>",<EOL>"<STR_LIT>": "<STR_LIT:U+0020>".join(station_codes),<EOL>"<STR_LIT>": -<NUM_LIT:1>,<EOL>},<EOL>)<EOL>resp.raise_for_status()<EOL>list(map(variables.add, rvar.findall(resp.text)))<EOL>return variables<EOL>
Internal helper to list the variables for the given station codes.