How to use the nova.i18n._ function in nova

msg = _("Requested network does not contain "
                            "enough (2+) usable hosts")
                    raise exc.HTTPBadRequest(explanation=msg)
            except netexc.AddrFormatError:
                msg = _("CIDR is malformed.")
                raise exc.HTTPBadRequest(explanation=msg)
            except netexc.AddrConversionError:
                msg = _("Address could not be converted.")
                raise exc.HTTPBadRequest(explanation=msg)

        networks = []
        try:
            if CONF.enable_network_quota:
                reservation = QUOTAS.reserve(context, networks=1)
        except exception.OverQuota:
            msg = _("Quota exceeded, too many networks.")
            raise exc.HTTPBadRequest(explanation=msg)

        kwargs['project_id'] = context.project_id

        try:
            networks = self.network_api.create(context,
                                               label=label, **kwargs)
            if CONF.enable_network_quota:
                QUOTAS.commit(context, reservation)
        except exception.PolicyNotAuthorized as e:
            raise exc.HTTPForbidden(explanation=six.text_type(e))
        except exception.CidrConflict as e:
            raise exc.HTTPConflict(explanation=e.format_message())
        except Exception:
            if CONF.enable_network_quota:
                QUOTAS.rollback(context, reservation)

class FloatingIpPoolNotFound(NotFound):
    msg_fmt = _("Floating IP pool not found.")
    safe = True


class NoMoreFloatingIps(FloatingIpNotFound):
    msg_fmt = _("Zero floating IPs available.")
    safe = True


class FloatingIpAssociated(NovaException):
    msg_fmt = _("Floating IP %(address)s is associated.")


class FloatingIpNotAssociated(NovaException):
    msg_fmt = _("Floating IP %(address)s is not associated.")


class NoFloatingIpsDefined(NotFound):
    msg_fmt = _("Zero floating IPs exist.")


class NoFloatingIpInterface(NotFound):
    msg_fmt = _("Interface %(interface)s not found.")


class FloatingIpAllocateFailed(NovaException):
    msg_fmt = _("Floating IP allocate failed.")


class FloatingIpAssociateFailed(NovaException):
    msg_fmt = _("Floating IP %(address)s association has failed.")

# be rolled up at the end of the check() function. These functions are
    # intended to be run in order and build on top of each other so order
    # matters.
    _upgrade_checks = (
        # Added in Ocata
        (_('Cells v2'), _check_cellsv2),
        # Added in Ocata
        (_('Placement API'), _check_placement),
        # Added in Rocky (but also useful going back to Pike)
        (_('Ironic Flavor Migration'), _check_ironic_flavor_migration),
        # Added in Rocky
        (_('Request Spec Migration'), _check_request_spec_migration),
        # Added in Stein (but also useful going back to Rocky)
        (_('Console Auths'), _check_console_auths),
        # Added in Train
        (_('Cinder API'), _check_cinder),
    )


CATEGORIES = {
    'upgrade': UpgradeCommands,
}


add_command_parsers = functools.partial(cmd_common.add_command_parsers,
                                        categories=CATEGORIES)


category_opt = cfg.SubCommandOpt('category',
                                 title='Command categories',
                                 help='Available categories',
                                 handler=add_command_parsers)

def _get_kstat_by_name(self, kstat_class, module, instance, name):
        """Return Kstat snapshot data via RAD as a dictionary."""
        pattern = {
            'class':    kstat_class,
            'module':   module,
            'instance': instance,
            'name':     name
        }
        try:
            self._kstat_control.update()
            kstat_object = self.rad_connection.get_object(
                kstat.Kstat(), rad.client.ADRGlobPattern(pattern))
        except Exception as reason:
            LOG.info(_("Unable to retrieve kstat object '%s:%s:%s' of class "
                       "'%s' via kstat(3RAD): %s")
                     % (module, instance, name, kstat_class, reason))
            return None

        kstat_data = {}
        for named in kstat_object.fresh_snapshot().data.NAMED:
            kstat_data[named.name] = getattr(named.value,
                                             str(named.value.discriminant))
        return kstat_data

def __init__(self, driver, name, pool=None, snapshot=None,
                 read_only=False):
        client, ioctx = driver._connect_to_rados(pool)
        try:
            self.volume = tpool.Proxy(rbd.Image(ioctx, name,
                                                snapshot=snapshot,
                                                read_only=read_only))
        except rbd.ImageNotFound:
            with excutils.save_and_reraise_exception():
                LOG.debug("rbd image %s does not exist", name)
                driver._disconnect_from_rados(client, ioctx)
        except rbd.Error:
            with excutils.save_and_reraise_exception():
                LOG.exception(_("error opening rbd image %s"), name)
                driver._disconnect_from_rados(client, ioctx)

        self.driver = driver
        self.client = client
        self.ioctx = ioctx

class OsInfoNotFound(NotFound):
    msg_fmt = _("No configuration information found for operating system "
                "%(os_name)s")


class BuildRequestNotFound(NotFound):
    msg_fmt = _("BuildRequest not found for instance %(uuid)s")


class AttachInterfaceNotSupported(Invalid):
    msg_fmt = _("Attaching interfaces is not supported for "
                "instance %(instance_uuid)s.")


class AttachInterfaceWithQoSPolicyNotSupported(AttachInterfaceNotSupported):
    msg_fmt = _("Attaching interfaces with QoS policy is not supported for "
                "instance %(instance_uuid)s.")


class NetworksWithQoSPolicyNotSupported(Invalid):
    msg_fmt = _("Using networks with QoS policy is not supported for "
                "instance %(instance_uuid)s. (Network ID is %(network_id)s)")


class CreateWithPortResourceRequestOldVersion(Invalid):
    msg_fmt = _("Creating servers with ports having resource requests, like a "
                "port with a QoS minimum bandwidth policy, is not supported "
                "until microversion 2.72.")


class InvalidReservedMemoryPagesOption(Invalid):
    msg_fmt = _("The format of the option 'reserved_huge_pages' is invalid. "

instance, network_id, port_id, req_ip)
        except (exception.PortNotFound,
                exception.NetworkNotFound) as e:
            raise exc.HTTPNotFound(explanation=e.format_message())
        except (exception.FixedIpAlreadyInUse,
                exception.InterfaceAttachFailedNoNetwork,
                exception.NoMoreFixedIps,
                exception.PortInUse,
                exception.NetworkDuplicated,
                exception.NetworkAmbiguous,
                exception.PortNotUsable) as e:
            raise exc.HTTPBadRequest(explanation=e.format_message())
        except exception.InstanceIsLocked as e:
            raise exc.HTTPConflict(explanation=e.format_message())
        except NotImplementedError:
            msg = _("Network driver does not support this function.")
            raise webob.exc.HTTPNotImplemented(explanation=msg)
        except exception.InterfaceAttachFailed:
            msg = _("Failed to attach interface")
            raise webob.exc.HTTPInternalServerError(explanation=msg)
        except exception.InstanceInvalidState as state_error:
            common.raise_http_conflict_for_instance_invalid_state(state_error,
                    'attach_interface', server_id)

        return self.show(req, server_id, vif['id'])

"value": value,
                                        "aggregate_id": aggregate_id})
                if new_entries:
                    context.session.execute(
                        api_models.AggregateMetadata.__table__.insert(),
                        new_entries)

                return metadata
        except db_exc.DBDuplicateEntry:
            # a concurrent transaction has been committed,
            # try again unless this was the last attempt
            with excutils.save_and_reraise_exception() as ctxt:
                if attempt < max_retries - 1:
                    ctxt.reraise = False
                else:
                    msg = _("Add metadata failed for aggregate %(id)s "
                            "after %(retries)s retries") % \
                              {"id": aggregate_id, "retries": max_retries}
                    LOG.warning(msg)

def _check_body(self, body):
        if body is None or body == "":
            raise webob.exc.HTTPBadRequest(explanation=_("No request body"))

def validate_device_name(value):
    try:
        # NOTE (ndipanov): Do not allow empty device names
        #                  until assigning default values
        #                  are supported by nova.compute
        utils.check_string_length(value, 'Device name',
                                  min_length=1, max_length=255)
    except exception.InvalidInput:
        raise exception.InvalidBDMFormat(
            details=_("Device name empty or too long."))

    if ' ' in value:
        raise exception.InvalidBDMFormat(
            details=_("Device name contains spaces."))