code: async def add_unit(self, count=1, to=None):
          
          app_facade = client.ApplicationFacade.from_connection(self.connection)
  
          log.debug(
              'Adding %s unit%s to %s',
              count, '' if count == 1 else 's', self.name)
  
          result = await app_facade.AddUnits(
              application=self.name,
              placement=parse_placement(to) if to else None,
              num_units=count,
          )
  
          return await asyncio.gather(*[
              asyncio.ensure_future(self.model._wait_for_new('unit', unit_id))
              for unit_id in result.units
          ])
docs: Add one or more units to this application.
  
          :param int count: Number of units to add
          :param str to: Placement directive, e.g.::
              '23' - machine 23
              'lxc:7' - new lxc container on machine 7
              '24/lxc/3' - lxc container 3 or machine 24
  
              If None, a new machine is provisioned.