managers.py

from geopy import units, distance
from mezzanine.core.managers import CurrentSiteManager

class GeoManager(CurrentSiteManager):
    def near(self, latitude=None, longitude=None, distance_range=30):
        queryset = super(GeoManager, self).get_query_set()

        if not (latitude and longitude and distance_range):
          return queryset.none()

        latitude       = float(latitude)
        longitude      = float(longitude)
        distance_range = float(distance_range)

        rough_distance = units.degrees(arcminutes=units.nautical(kilometers=distance_range)) * 2

        queryset = queryset.filter(
            latitude__range=(
                latitude - rough_distance,
                latitude + rough_distance
            ),
            longitude__range=(
                longitude - rough_distance,
                longitude + rough_distance
            )
        )

        locations = []
        for location in queryset:
          if location.latitude and location.longitude:
            exact_distance = distance.distance(
                (latitude, longitude),
                (location.latitude, location.longitude)
            ).kilometers

            if exact_distance <= distance_range:
              locations.append(location)

        queryset = queryset.filter(id__in=[l.id for l in locations])
        return queryset

models.py

from geopy import geocoders
from geopy.geocoders.google import GQueryError

class BaseGeo(models.Model):
    location  = models.TextField(_('Address'), blank=True)
    latitude  = models.FloatField(_('Latitude'), blank=True, null=True)
    longitude = models.FloatField(_('Longitude'), blank=True, null=True)
    place     = models.TextField(_('Place'), blank=True)
    objects   = GeoManager()

    class Meta:
        abstract = True

    def save(self, domain='maps.google.com.my', *args, **kwargs):
        location = self.location
        if location:
            if not self.latitude or not self.longitude:
                try:
                    g = geocoders.Google(domain=domain)
                    self.place, (self.latitude, self.longitude) = g.geocode(location)
                except GQueryError:
                    pass
                except Exception, e:
                    print '%s' % e

        super(BaseGeo, self).save(*args, **kwargs)