from noc.ip.models import Prefix
from noc.lib.ip import IP

p = Prefix.objects.filter(vrf=12, Prefix_group="Clients-p2p", afi=4)
for pref in p:
    locked_prefixes = pref.nested_prefix_set
    locked = []
    free = []
    for lock in locked_prefixes:
        locked += {lock.prefix}
    del locked[0]
    for free_preffix in IP.prefix(pref.prefix).iter_free(locked):
        free_preffix