code: def resolve_file_format(args, import_files, export_file=None):
      if len(import_files) == 1:
          input_ext = os.path.splitext(import_files[0])[1]
          if input_ext == ".nnp" or input_ext == ".nntxt":
              args.import_format = "NNP"
          elif input_ext == ".onnx":
              args.import_format = "ONNX"
          elif input_ext == ".pb":
              args.import_format = "TF_PB"
          elif input_ext == ".ckpt":
              args.import_format = "TF_CKPT_V1"
          elif input_ext == ".meta":
              args.import_format = "TF_CKPT_V2"
          elif input_ext == ".tflite":
              args.import_format = "TFLITE"
          elif input_ext == "" and os.path.isdir(import_files[0]):
              args.import_format = "SAVED_MODEL"
  
      if export_file:
          output_ext = os.path.splitext(export_file)[1]
          if output_ext == ".nnp":
              args.export_format = "NNP"
          elif output_ext == ".nnb":
              args.export_format = "NNB"
          elif output_ext == ".onnx":
              args.export_format = "ONNX"
          elif output_ext == ".pb":
              args.export_format = "TF_PB"
          elif output_ext == ".tflite":
              args.export_format = "TFLITE"
          elif output_ext == "":
              logger.warning(
                  "The export file format is 'CSRC' or 'SAVED_MODEL' that argument '--export-format' will have to be set!!!"
              )
              assert (
                  args.export_format == "CSRC"
                  or args.export_format == "SAVED_MODEL"
              )
      else:
          args.export_format = ""
  
      if args.import_format in [
          "ONNX",
          "TF_CKPT_V1",
          "TF_CKPT_V2",
          "TF_PB",
          "SAVED_MODEL",
          "TFLITE",
      ] or args.export_format in [
          "ONNX",
          "TFLITE",
          "SAVED_MODEL",
          "TF_PB",
      ]:
          try:
              import nnabla.utils.converter.onnx
              import nnabla.utils.converter.tensorflow
          except ImportError:
              raise ImportError(
                  'nnabla_converter python package is not found, install nnabla_converter package with "pip install nnabla_converter"'
              )
  
file_path: nnabla/python/src/nnabla/utils/cli/convert.py
imports: import os
  import nnabla.logger
  import nnabla.utils.converter
label_desc: Use image node_id 3 for calling a global function with example usage: resolve_file_format(args, import_files, export_file) without return types