code: def _checkFileExists(self):
          
          if self._fileName and not os.path.exists(self._fileName):
              msg = "File not found: {}".format(self._fileName)
              logger.error(msg)
              self.setException(IOError(msg))
              return False
          else:
              return True
docs: Verifies that the underlying file exists and sets the _exception attribute if not
              Returns True if the file exists.
              If self._fileName is None, nothing is checked and True is returned.