Django queryset for objects within X long/lat radius

distance.py

# Simple version of Django queryset for objects within X long/lat radius
import math

def get_queryset(self):
    user = self.request.user
    lat = self.request.query_params.get('lat', None)
    lon = self.request.query_params.get('long', None)

    if lat and lon:
        lat = float(lat)
        lon = float(lon)

        R = 6378.1  # earth radius
        distance = 10  # distance in km

        lat1 = lat - math.degrees(distance / R)
        lat2 = lat + math.degrees(distance / R)
        long1 = lon - math.degrees(distance / R / math.cos(math.degrees(lat)))
        long2 = lon + math.degrees(distance / R / math.cos(math.degrees(lat)))
        queryset = UserDetail.objects.filter(current_lat__gte=lat1, current_lat__lte=lat2)\
            .filter(current_long__gte=long1, current_long__lte=long2)