code: def main(argv):
      if len(argv) not in (2, 3):
          print(
              "Usage: %s <input_filename> [<output_filename>]" % argv[0]
          )
          sys.exit(1)
  
      input_filename = argv[1]
      output_filename = None if len(argv) == 2 else argv[2]
  
      try:
          convert(input_filename, output_filename)
      except ConversionError as e:
          print("Could not execute conversion:", e)
          sys.exit(1)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import re
  import sys
  import time
  from absl import app
  from absl import logging
  from third_party.nucleus.io import bed
  from third_party.nucleus.io import fastq
  from third_party.nucleus.io import gff
  from third_party.nucleus.io import sam
  from third_party.nucleus.io import vcf
label_desc: Use image node_id 6 for calling a global function with example usage: main(argv) without return types