code: def list_images(self, identifier, offset=-1, limit=-1):
          
          # Get image group to ensure that it exists. The object contains the full
          # list of group images
          img_grp = self.get_object(identifier)
          if img_grp is None:
              return None
          # Extract subset of group images based on offset and limit arguments
          total_count = len(img_grp.images)
          items = []
          if offset < total_count:
              if limit > 0:
                  list_end = min((offset + limit), total_count)
              else:
                  list_end = total_count
              for i in range(offset, list_end):
                  items.append(img_grp.images[i])
          # Return object listing
          return datastore.ObjectListing(items, offset, limit, total_count)
docs: Parameters
          ----------
          identifier : string
              Unique image group identifier
          limit : int
              Limit number of results in returned object listing
          offset : int
              Set offset in list (order as defined by object store)
  
          Returns
          -------
          ObjectListing
              Listing of group images or None if image group does not exist