code: def create_session(self, **params):
          
          return self.make_request(self.PRICING_SESSION_URL,
                                   method='post',
                                   headers=self._session_headers(),
                                   callback=lambda resp: resp.headers[
                                       'location'],
                                   data=params)
docs: Create the session
          date format: YYYY-mm-dd
          location: ISO code