code: def _gen_full_path(self, filename, file_system=None):
          
          if file_system is None:
              return '{}/{}'.format(self.dest_file_system, filename)
          else:
              if ":" not in file_system:
                  raise ValueError("Invalid file_system specified: {}".format(file_system))
              return '{}/{}'.format(file_system, filename)
docs: Generate full file path on remote device.