code: def _call_proc(self,
                     proc: Callable[[Optional[str], Optional[str], argparse.Namespace], bool],
                     ifn: Optional[str],
                     ofn: Optional[str]) -> bool:
          
          rslt = False
          try:
              rslt = proc(ifn, ofn, self.opts)
          except Exception as e:
              self._proc_error(ifn, e)
          return True if rslt or rslt is None else False
docs: Call the actual processor and intercept anything that goes wrong
          :param proc: Process to call
          :param ifn: Input file name to process.  If absent, typical use is stdin
          :param ofn: Output file name. If absent, typical use is stdout
          :return: true means process was successful