code: def explode(self, hosts, hostgroups, contactgroups):
          
          for i in self:
              # items::explode_host_groups_into_hosts
              # take all hosts from our hostgroup_name into our host_name property
              self.explode_host_groups_into_hosts(i, hosts, hostgroups)
  
              # items::explode_contact_groups_into_contacts
              # take all contacts from our contact_groups into our contact property
              self.explode_contact_groups_into_contacts(i, contactgroups)
docs: Loop over all escalation and explode hostsgroups in host
          and contactgroups in contacts
  
          Call Item.explode_host_groups_into_hosts and Item.explode_contact_groups_into_contacts
  
          :param hosts: host list to explode
          :type hosts: alignak.objects.host.Hosts
          :param hostgroups: hostgroup list to explode
          :type hostgroups: alignak.objects.hostgroup.Hostgroups
          :param contactgroups: contactgroup list to explode
          :type contactgroups: alignak.objects.contactgroup.Contactgroups
          :return: None