human
I wrote the below code

    if ((lat is None) or (lon is None) or (not os.path.isdir(cache_dir))):
        return
    stations = bom_stations(cache_dir)
    def comparable_dist(wmo_id):
        'Create    a    psudeo-distance    from    lat/lon.'
        (station_lat, station_lon) = stations[wmo_id]
        return (((lat - station_lat) ** 2) + ((lon - station_lon) ** 2))
    return min(stations, key=comparable_dist)

What's a good function header?

=====
Here's a good function header?
assistant
#Here's a good function header.

def closest_station(lat, lon, cache_dir):