def _fit_called(self) -> bool:
        """
        Returns whether all the transformers in the pipeline were fitted (when applicable).

        Returns
        -------
        bool
            `True` if all the fittable transformers are fitted, `False` otherwise
        """
        return all(
            (not isinstance(t, FittableDataTransformer)) or t._fit_called
            for t in self._transformers
        )

        Returns whether all the transformers in the pipeline were fitted (when applicable).

        Returns
        -------
        bool
            `True` if all the fittable transformers are fitted, `False` otherwise
        
darts/dataprocessing/pipeline.py