Method undo

tables/file.py:2723–2766

Go to a past state of the database. Returns the database to the state associated with the specified mark. Both the identifier of a mark and its name can be used. If the mark is omitted, the last created mark is used. If there are no past marks, or the specified mark

(self, mark: int | str | None = None)

            self._curaction += direction

    def undo(self, mark: int | str | None = None) -> None:
        """Go to a past state of the database.

        Returns the database to the state associated with the specified mark.
        Both the identifier of a mark and its name can be used. If the mark is
        omitted, the last created mark is used. If there are no past
        marks, or the specified mark is not older than the current one, an
        UndoRedoError is raised.

        This method can only be called when the Undo/Redo mechanism
        has been enabled. Otherwise, an UndoRedoError
        is raised.

        """
        self._check_open()
        self._check_undo_enabled()

        #         print("(pre)UNDO: (curaction, curmark) = (%s,%s)" % \
        #               (self._curaction, self._curmark))
        if mark is None:
            markid = self._curmark
            # Correction if we are settled on top of a mark
            opcode = self._actionlog.cols.opcode
            if opcode[self._curaction] == _op_to_code["MARK"]:
                markid -= 1
        else:
            # Get the mark ID number
            markid = self._get_mark_id(mark)
        # Get the final action ID to go
        finalaction = self._get_final_action(markid)
        if finalaction > self._curaction:
            raise UndoRedoError(
                "Mark ``%s`` is newer than the current mark. "
                "Use `redo()` or `goto()` instead." % (mark,)
            )

        # The file is going to be changed.
        self._check_writable()

        # Try to reach this mark by unwinding actions in the log
        self._doundo(finalaction - 1, -1)
        if self._curaction < self._actionlog.nrows - 1:
            self._curaction += 1
        self._curmark = int(self._actionlog.cols.arg1[self._curaction])

    #         print("(post)UNDO: (curaction, curmark) = (%s,%s)" % \
    #               (self._curaction, self._curmark))