code: def fname(self, version=None, tags=None, ext=None):
          
          if ext is None:
              ext = self.default_ext
          return '{}{}{}.{}'.format(
              self.fname_base,
              self._tags_to_str(tags=tags),
              self._version_to_str(version=version),
              ext,
          )
docs: Returns the filename appropriate for an instance of this dataset.
  
          Parameters
          ----------
          version: str, optional
              The version of the instance of this dataset.
          tags : list of str, optional
              The tags associated with the instance of this dataset.
          ext : str, optional
              The file extension to use. If not given, the default extension is
              used.
  
          Returns
          -------
          str
              The appropariate filename.