class_docstr: File handler for NC seviri files.
  
  **Calibration**
  
  See :mod:`satpy.readers.seviri_base`. Note that there is only one set of
  calibration coefficients available in the netCDF files and therefore there
  is no `calib_mode` argument.
  
  **Metadata**
  
  See :mod:`satpy.readers.seviri_base`.
docstr: Get coefficients for calibration from counts to radiance.
code: def _get_calib_coefs(self, dataset, channel):
      """Get coefficients for calibration from counts to radiance."""
      band_idx = list(CHANNEL_NAMES.values()).index(channel)
      offset = dataset.attrs["add_offset"].astype("float32")
      gain = dataset.attrs["scale_factor"].astype("float32")
      # Only one calibration available here
      return {
          "coefs": {
              "NOMINAL": {"gain": gain, "offset": offset},
              "EXTERNAL": self.ext_calib_coefs.get(channel, {}),
          },
          "radiance_type": self.nc["planned_chan_processing"].values[
              band_idx
          ],
      }
  
imports: import datetime
  import logging
  from datetime import timedelta
  import numpy
  from satpy._compat import cached_property
  from satpy.readers._geos_area import get_area_definition, get_geos_area_naming
  from satpy.readers.eum_base import get_service_mode
  from satpy.readers.file_handlers import BaseFileHandler, open_dataset
  from satpy.readers.seviri_base import CHANNEL_NAMES, SATNUM, NoValidOrbitParams, OrbitPolynomialFinder, SEVIRICalibrationHandler, add_scanline_acq_time, get_cds_time, get_satpos, mask_bad_quality, round_nom_time
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 13 for calling the NCSEVIRIFileHandler obj's underlying member method code with example usage: obj._get_calib_coefs(dataset, channel) and returns: dict