code: def weather_at_zip_code(self, zipcode, country):
          
          assert isinstance(zipcode, str), "Value must be a string"
          assert isinstance(country, str), "Value must be a string"
          encoded_zip = zipcode
          encoded_country = country
          zip_param = encoded_zip + ',' + encoded_country
          params = {'zip': zip_param, 'lang': self._language}
          uri = http_client.HttpClient.to_url(OBSERVATION_URL,
                                              self._API_key,
                                              self._subscription_type,
                                              self._use_ssl)
          _, json_data = self._wapi.cacheable_get_json(uri, params=params)
          return self._parsers['observation'].parse_JSON(json_data)
docs: Queries the OWM Weather API for the currently observed weather at the
          specified zip code and country code (eg: 2037, au).
          
          :param zip: the location's zip or postcode
          :type zip: string
          :param country: the location's country code
          :type country: string
          :returns: an *Observation* instance or ``None`` if no weather data is
              available
          :raises: *ParseResponseException* when OWM Weather API responses' data
              cannot be parsed or *APICallException* when OWM Weather API can not be
              reached