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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _internal_network_removed(self, ri, port, ex_gw_port):
 """Remove an internal router port Check to see if this is the last port to be removed for a given network scoped by a VRF (note: there can be different mappings between VRFs and networks -- 1-to-1, 1-to-n, n-to-1, n-to-n -- depending on the configuration and workflow used). If it is the last port, set the flag indicating that the internal sub-interface for that netowrk on the ASR should be deleted """

        itfc_deleted = False
        driver = self.driver_manager.get_driver(ri.id)
        vrf_name = driver._get_vrf_name(ri)
        network_name = ex_gw_port['hosting_info'].get('network_name')
        if self._router_ids_by_vrf_and_ext_net.get(
            vrf_name, {}).get(network_name) and (
                ri.router['id'] in
                self._router_ids_by_vrf_and_ext_net[vrf_name][network_name]):
            # If this is the last port for this neutron router,
            # then remove this router from the list
            if len(ri.internal_ports) == 1 and port in ri.internal_ports:
                self._router_ids_by_vrf_and_ext_net[
                    vrf_name][network_name].remove(ri.router['id'])

                # Check if any other routers in this VRF have this network,
                # and if not, set the flag to remove the interface
                if not self._router_ids_by_vrf_and_ext_net[vrf_name].get(
                        network_name):
                    LOG.debug("++ REMOVING NETWORK %s" % network_name)
                    itfc_deleted = True
                    del self._router_ids_by_vrf_and_ext_net[
                        vrf_name][network_name]
                    if not self._router_ids_by_vrf_and_ext_net.get(vrf_name):
                        del self._router_ids_by_vrf_and_ext_net[vrf_name]

        driver.internal_network_removed(ri, port,
                                        itfc_deleted=itfc_deleted)
        if ri.snat_enabled and ex_gw_port:
            driver.disable_internal_network_NAT(ri, port, ex_gw_port,
                                                itfc_deleted=itfc_deleted)