I've used Geocoder, a good Python library that supports multiple providers, including Google, Geonames, and OpenStreetMaps, to mention just a few. I've tried using the GeoPy library, and it often gets timeouts. Developing your own code for GeoNames is not the best use of your time and you may end up getting unstable code. Geocoder is very simple to use in my experience, and has good enough documentation. Below is some sample code for looking up city by latitude and longitude, or finding latitude/longitude by city name.
import geocoder
g = geocoder.osm([53.5343609, -113.5065084], method='reverse')
print g.json['city'] # Prints Edmonton
g = geocoder.osm('Edmonton, Canada')
print g.json['lat'], g.json['lng'] # Prints 53.5343609, -113.5065084