class_docstr: NWCSAF PPS&MSG NetCDF reader.
code: def _prepare_variable_for_palette(self, variable, info):
      try:
          so_dataset = self.nc[
              self._get_varname_in_file(
                  info, info_type="scale_offset_dataset"
              )
          ]
      except KeyError:
          scale = 1
          offset = 0
          fill_value = 255
      else:
          scale = so_dataset.attrs["scale_factor"]
          offset = so_dataset.attrs["add_offset"]
          fill_value = so_dataset.attrs["_FillValue"]
      variable.attrs["palette_meanings"] = [
          int(val) for val in variable.attrs["palette_meanings"].split()
      ]
  
      if (
          fill_value not in variable.attrs["palette_meanings"]
          and "fill_value_color" in variable.attrs
      ):
          variable.attrs["palette_meanings"] = [
              fill_value
          ] + variable.attrs["palette_meanings"]
          variable = xr.DataArray(
              da.vstack(
                  (
                      np.array(variable.attrs["fill_value_color"]),
                      variable.data,
                  )
              ),
              coords=variable.coords,
              dims=variable.dims,
              attrs=variable.attrs,
          )
      val, idx = np.unique(
          variable.attrs["palette_meanings"], return_index=True
      )
      variable.attrs["palette_meanings"] = val * scale + offset
      variable = variable[idx]
      return variable
  
imports: import functools
  import logging
  import os
  from contextlib import suppress
  from datetime import datetime
  import dask.array
  import numpy
  import xarray
  from pyproj import CRS
  from pyresample.geometry import AreaDefinition
  from satpy.readers.file_handlers import BaseFileHandler
  from satpy.readers.utils import unzip_file
  from satpy.utils import get_chunk_size_limit
label_desc: Use image node_id 11 for calling the NcNWCSAF obj's underlying member method code with example usage: obj._prepare_variable_for_palette(variable, info) and returns: variable