code: def _get_channel_index(key):
      """Get the avhrr channel index."""
      avhrr_channel_index = {
          "1": 0,
          "2": 1,
          "3a": 2,
          "3b": 2,
          "4": 3,
          "5": 4,
      }
      index = avhrr_channel_index[key["name"]]
      return index
  
imports: import logging
  from datetime import datetime
  import dask.array
  import numpy
  import xarray
  from geotiepoints import SatelliteInterpolator
  from pyorbital.geoloc import compute_pixels, get_lonlatalt
  from pyorbital.geoloc_instrument_definitions import avhrr
  from pyorbital.orbital import Orbital
  from satpy._compat import cached_property
  from satpy.readers.aapp_l1b import get_avhrr_lac_chunks
  from satpy.readers.file_handlers import BaseFileHandler
label_desc: Use image node_id 4 for calling a global function with example usage: _get_channel_index(key) and returns: index