How to use the jupyterhub.utils.isoformat function in jupyterhub

spawner = user.orm_spawners[server_name]

                if (not spawner.last_activity) or last_activity > spawner.last_activity:
                    self.log.debug(
                        "Activity on server %s/%s: %s",
                        user.name,
                        server_name,
                        isoformat(last_activity),
                    )
                    spawner.last_activity = last_activity
                else:
                    self.log.debug(
                        "Not updating server activity on %s/%s: %s < %s",
                        user.name,
                        server_name,
                        isoformat(last_activity),
                        isoformat(user.last_activity),
                    )

        self.db.commit()

if (not spawner.last_activity) or last_activity > spawner.last_activity:
                    self.log.debug(
                        "Activity on server %s/%s: %s",
                        user.name,
                        server_name,
                        isoformat(last_activity),
                    )
                    spawner.last_activity = last_activity
                else:
                    self.log.debug(
                        "Not updating server activity on %s/%s: %s < %s",
                        user.name,
                        server_name,
                        isoformat(last_activity),
                        isoformat(user.last_activity),
                    )

        self.db.commit()

def server_model(self, spawner, include_state=False):
        """Get the JSON model for a Spawner"""
        return {
            'name': spawner.name,
            'last_activity': isoformat(spawner.orm_spawner.last_activity),
            'started': isoformat(spawner.orm_spawner.started),
            'pending': spawner.pending,
            'ready': spawner.ready,
            'state': spawner.get_state() if include_state else None,
            'url': url_path_join(spawner.user.url, spawner.name, '/'),
            'user_options': spawner.user_options,
            'progress_url': spawner._progress_url,
        }

(we use naïve utc timestamps everywhere)
    """
    try:
        dt = parse_date(timestamp)
    except Exception:
        raise web.HTTPError(400, "Not a valid timestamp: %r", timestamp)
    if dt.tzinfo:
        # strip timezone info to naïve UTC datetime
        dt = dt.astimezone(timezone.utc).replace(tzinfo=None)

    now = datetime.utcnow()
    if (dt - now) > timedelta(minutes=59):
        raise web.HTTPError(
            400,
            "Rejecting activity from more than an hour in the future: {}".format(
                isoformat(dt)
            ),
        )
    return dt

if token.user:
            owner_key = 'user'
            owner = token.user.name

        else:
            owner_key = 'service'
            owner = token.service.name

        model = {
            owner_key: owner,
            'id': token.api_id,
            'kind': kind,
            'created': isoformat(token.created),
            'last_activity': isoformat(token.last_activity),
            'expires_at': isoformat(expires_at),
        }
        model.update(extra)
        return model

)

        if token.user:
            owner_key = 'user'
            owner = token.user.name

        else:
            owner_key = 'service'
            owner = token.service.name

        model = {
            owner_key: owner,
            'id': token.api_id,
            'kind': kind,
            'created': isoformat(token.created),
            'last_activity': isoformat(token.last_activity),
            'expires_at': isoformat(expires_at),
        }
        model.update(extra)
        return model

def user_model(self, user, include_servers=False, include_state=False):
        """Get the JSON model for a User object"""
        if isinstance(user, orm.User):
            user = self.users[user.id]

        model = {
            'kind': 'user',
            'name': user.name,
            'admin': user.admin,
            'groups': [g.name for g in user.groups],
            'server': user.url if user.running else None,
            'pending': None,
            'created': isoformat(user.created),
            'last_activity': isoformat(user.last_activity),
        }
        if '' in user.spawners:
            model['pending'] = user.spawners[''].pending

        if not include_servers:
            model['servers'] = None
            return model

        servers = model['servers'] = {}
        for name, spawner in user.spawners.items():
            # include 'active' servers, not just ready
            # (this includes pending events)
            if spawner.active:
                servers[name] = self.server_model(spawner, include_state=include_state)
        return model