Note: if title is None, will be replaced with obj.filename

def use(self, obj, parent_form=None):
        """Note: if title is None, will be replaced with obj.filename
        """

        if not isinstance(obj, self.input_classes):
            raise RuntimeError('{0!s} cannot handle a {1!s}'.format(self.__class__.__name__, obj.__class__.__name__))

        self.parent_form = parent_form

        if self.title is None:
            self.title = 'file: '+obj.filename
        self._do_use(obj)