code: def _compute_scale(self, instruction_id, svg_dict):
          
          bbox = list(map(float, svg_dict["svg"]["@viewBox"].split()))
          scale = self._zoom / (bbox[3] - bbox[1])
          self._symbol_id_to_scale[instruction_id] = scale
docs: Compute the scale of an instruction svg.
  
          Compute the scale using the bounding box stored in the
          :paramref:`svg_dict`. The scale is saved in a dictionary using
          :paramref:`instruction_id` as key.
  
          :param str instruction_id: id identifying a symbol in the defs
          :param dict svg_dict: dictionary containing the SVG for the
            instruction currently processed