old_contents: from core.models import Network
  from deleter import Deleter
  
  class NetworkDeleter(Deleter):
      model='Network'
  
      def call(self, pk):
          network = Network.objects.get(pk=pk) 
          if (network.router_id) and (network.subnet_id):
              self.driver.delete_router_interface(network.router_id, network.subnet_id)
          if network.subnet_id:
              self.driver.delete_subnet(network.subnet_id)
          if network.router_id:
              self.driver.delete_router(network.router_id)
          if network.network_id:
              self.driver.delete_network(network.network_id)
          network.delete()
  
new_contents: from core.models import Network
  from observer.deleter import Deleter
  
  class NetworkDeleter(Deleter):
      model='Network'
  
      def call(self, pk):
          network = Network.objects.get(pk=pk) 
          if (network.router_id) and (network.subnet_id):
              self.driver.delete_router_interface(network.router_id, network.subnet_id)
          if network.subnet_id:
              self.driver.delete_subnet(network.subnet_id)
          if network.router_id:
              self.driver.delete_router(network.router_id)
          if network.network_id:
              self.driver.delete_network(network.network_id)
          network.delete()
  
subject: fix import error