Method enable_undo

tables/file.py:2388–2486

Enable the Undo/Redo mechanism. This operation prepares the database for undoing and redoing modifications in the node hierarchy. This allows :meth:`File.mark`, :meth:`File.undo`, :meth:`File.redo` and other methods to be called. The filters argument, when s

(self, filters: Filters = Filters(complevel=1))

        return MarkG(trans, _mark_name % mid, "Mark number %d" % mid, new=True)

    def enable_undo(self, filters: Filters = Filters(complevel=1)) -> None:
        """Enable the Undo/Redo mechanism.

        This operation prepares the database for undoing and redoing
        modifications in the node hierarchy. This
        allows :meth:`File.mark`, :meth:`File.undo`, :meth:`File.redo` and
        other methods to be called.

        The filters argument, when specified,
        must be an instance of class Filters (see :ref:`FiltersClassDescr`) and
        is meant for setting the compression values for the action log. The
        default is having compression enabled, as the gains in terms of
        space can be considerable. You may want to disable compression if
        you want maximum speed for Undo/Redo operations.

        Calling this method when the Undo/Redo mechanism is already
        enabled raises an UndoRedoError.

        """
        maxundo = self.params["MAX_UNDO_PATH_LENGTH"]

        class ActionLog(NotLoggedMixin, Table):
            pass

        class ActionLogDesc(IsDescription):
            opcode = UInt8Col(pos=0)
            arg1 = StringCol(maxundo, pos=1, dflt=b"")
            arg2 = StringCol(maxundo, pos=2, dflt=b"")

        self._check_open()

        # Enabling several times is not allowed to avoid the user having
        # the illusion that a new implicit mark has been created
        # when calling enable_undo for the second time.

        if self.is_undo_enabled():
            raise UndoRedoError("Undo/Redo feature is already enabled!")

        self._markers: dict[str, int] = {}
        self._seqmarkers: list[int] = []
        self._nmarks = 0
        self._curtransaction = 0
        self._curmark = -1  # No marks yet

        # Get the Group for keeping user actions
        try:
            tgroup = self.get_node(_trans_group_path)
        except NodeError:
            # The file is going to be changed.
            self._check_writable()

            # A transaction log group does not exist. Create it
            tgroup = self._create_transaction_group()

            # Create a transaction.
            self._trans = self._create_transaction(
                tgroup, self._curtransaction
            )