Helper to filter the closest station to a given location.

def _filter_closest(self, lat, lon, stations):
        """Helper to filter the closest station to a given location."""
        current_location = (lat, lon)
        closest = None
        closest_distance = None

        for station in stations:
            station_loc = (station.latitude, station.longitude)
            station_distance = distance.distance(current_location,
                                                 station_loc).km
            if not closest or station_distance < closest_distance:
                closest = station
                closest_distance = station_distance

        return closest