code: def _memcache_key(self, timestamped=False):
          
          request = tuple(map(str, self.package_requests))
          repo_ids = []
          for path in self.package_paths:
              repo = package_repository_manager.get_repository(path)
              repo_ids.append(repo.uid)
  
          t = ["resolve",
               request,
               tuple(repo_ids),
               self.package_filter_hash,
               self.package_orderers_hash,
               self.building,
               config.prune_failed_graph]
  
          if timestamped and self.timestamp:
              t.append(self.timestamp)
  
          return str(tuple(t))
docs: Makes a key suitable as a memcache entry.