osm_reverse_geocode.py

import requests
try:
    from urllib.parse import urlencode
except ImportError:
    from urllib import urlencode


def reverse_geocode(lng, lat, zoom=18):
    OSM_API_URL = 'http://nominatim.openstreetmap.org/reverse?'
    _headers = {'User-Agent': 
                'Identify your application in accordance with Nominatim API Usage Policy'}
    params = {'format': 'json', 'zoom': zoom, 'lon': lng, 'lat': lat}
    r = requests.get(OSM_API_URL + urlencode(params), headers=_headers)
    if r.status_code == 200:
        return r.json()
    elif r.status_code == 404:
        raise ValueError
    else:
        raise ConnectionError

Nominatim Usage Policy