class_docstr: A base class for the CLAVRx File Handlers.
class_docstr_tok: ["A","base","class","for","the","CLAVRx","File","Handlers","."]
code: def _find_input_nc(filename: str, l1b_base: str) -> str:
      dirname = os.path.dirname(filename)
      l1b_filename = os.path.join(dirname, l1b_base + ".nc")
      if os.path.exists(l1b_filename):
          return str(l1b_filename)
  
      glob_pat = os.path.join(dirname, l1b_base + "*R20*.nc")
      LOG.debug("searching for {0}".format(glob_pat))
      found_l1b_filenames = list(glob(glob_pat))
      if len(found_l1b_filenames) == 0:
          raise IOError(
              "Could not find navigation donor for {0}"
              " in same directory as CLAVR-x data".format(l1b_base)
          )
      LOG.debug(
          "Candidate nav donors: {0}".format(repr(found_l1b_filenames))
      )
      return found_l1b_filenames[0]
  
imports: import logging
  import os
  from glob import glob
  from typing import Optional, Union
  import netCDF4
  import numpy
  import xarray
  from pyresample import geometry
  from satpy.readers.file_handlers import BaseFileHandler
  from satpy.readers.hdf4_utils import SDS, HDF4FileHandler
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 6 for calling the _CLAVRxHelper obj's underlying member method code with example usage: obj._find_input_nc(filename, l1b_base) and returns: found_l1b_filenames, str