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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def query_rates(self, pairs=[]):
        ''' Perform a request against truefx data '''
        # If no pairs, TrueFx will use the ones given the last time
        payload = {'id': self._session}
        if pairs:
            payload['c'] = _clean_pairs(pairs)
        response = requests.get(self._api_url, params=payload)

        mapped_data = _fx_mapping(response.content.split('\n')[:-2])
        return Series(mapped_data) if len(mapped_data) == 1 \
            else DataFrame(mapped_data)