code: def _cache(self, key, val):
          
          cache_size = (1 if util.dimensionless_contents(self.streams, self.kdims)
                        else self.cache_size)
          if len(self) >= cache_size:
              first_key = next(k for k in self.data)
              self.data.pop(first_key)
          self[key] = val
docs: Request that a key/value pair be considered for caching.