def flattened(self, flattened: list[Any]) -> None:
        """Setter to conveniently update the list of iterables."""
        if len(flattened) != len(self._flattened):
            raise ValueError(
                f"Mismatch in flattened length ({len(flattened)}) and existing length ({len(self._flattened)})"
            )
        # update the iterable collection
        self._iterables = tree_unflatten(flattened, self._spec)
        self._flattened = flattened
Setter to conveniently update the list of iterables.
src/lightning/pytorch/utilities/combined_loader.py