Method _update_source

traitlets/traitlets.py:347–355

(self, change: t.Any)

                )

    def _update_source(self, change: t.Any) -> None:
        if self.updating:
            return
        with self._busy_updating():
            setattr(self.source[0], self.source[1], self._transform_inv(change.new))
            if getattr(self.target[0], self.target[1]) != change.new:
                raise TraitError(
                    f"Broken link {self}: the target value changed while updating " "the source."
                )

    def unlink(self) -> None:
        self.source[0].unobserve(self._update_target, names=self.source[1])