code: def run(self):
          
          for line in self.incoming:
              message = loads(line)
              result = self._evaluate(message)
              if result is self._SKIP:
                  continue
              self.output.write(dumps(result, cls=_DatetimeJSONEncoder) + b"\n")
docs: For each incoming message, decode the JSON, evaluate expression, encode
          as JSON and write that to the output file.