code: def load_idx_cont(self, idx_spec, loader_cont_fn, **kwargs):
          
          if len(self) == 0:
              raise ValueError("Please call open_file() first!")
  
          idx_lst = self.get_matching_indexes(idx_spec)
          if len(self) == 0:
              raise ValueError("Please call open_file() first!")
  
          for i in idx_lst:
              try:
                  dst_obj = self.get_hdu(i, **kwargs)
  
                  loader_cont_fn(dst_obj)
  
              except Exception as e:
                  self.logger.error("Error loading index '%s': %s" % (i, str(e)))
docs: Parameters
          ----------
          idx_spec : str
              A string in the form of a pair of brackets enclosing some
              index expression matching HDUs in the file
  
          loader_cont_fn : func (data_obj) -> None
              A loader continuation function that takes a data object
              generated from loading an HDU and does something with it
  
          kwargs : optional keyword arguments
              Any optional keyword arguments are passed to the code that
              loads the data from the file