code: def full_parser():
      
      global _full_parser
  
      if _full_parser:
          return _full_parser
  
      luigi_parser = luigi.cmdline_parser.CmdlineParser.get_instance()
      if not luigi_parser:
          return None
  
      # build the full argument parser with luigi helpers
      root_task = luigi_parser.known_args.root_task
      _full_parser = luigi_parser._build_parser(root_task)
  
      logger.debug("build full luigi argument parser")
  
      return _full_parser
docs: Returns the full *ArgumentParser* used by the luigi ``CmdlineParser``. The returned instance is
      cached.