def start_box_selection(self):
        """Prepare for box selection mode and set it."""
        ### store current mouse pos
        self.initial_box_pos = SERVICES_NS.get_mouse_pos()

        ### get a copy of the scrolling amount by adding
        ### (0, 0) to it and store the copy as the initial
        ### scrolling
        self.initial_scrolling = self.scrolling_amount + (0, 0)

        ### create a rect with arbitrary values,
        ### representing a selection box
        self.selection_box = Rect(0, 0, 0, 0)

        ### set behaviour related to box selection in the
        ### window manager and go to beginning of the app
        ### loop

        APP_REFS.wm.set_state("box_selection")
        raise ContinueLoopException
Prepare for box selection mode and set it.
nodezator/editing/selection.py