code: def download(cls, filename, input_dir, dl_dir=None):
          
          file_info = cls.parse_remote(filename)
          if not dl_dir:
              dl_dir = os.path.join(input_dir, file_info.bucket,
                                    os.path.dirname(file_info.key))
              utils.safe_makedir(dl_dir)
  
          out_file = os.path.join(dl_dir, os.path.basename(file_info.key))
  
          if not utils.file_exists(out_file):
              with file_transaction({}, out_file) as tx_out_file:
                  command, prog = cls._download_cl(filename)
                  if prog == "gof3r":
                      command.extend(["-p", tx_out_file])
                  elif prog == "awscli":
                      command.extend([tx_out_file])
                  else:
                      raise NotImplementedError(
                          "Unexpected download program %s" % prog)
                  subprocess.check_call(command)
          return out_file
docs: Provide potentially streaming download from S3 using gof3r
          or the AWS CLI.