class_docstr: Helper function for downloading external dependency
  
  >>> from nlpaug.util.file.download import DownloadUtil
code: def download_back_translation(dest_dir):
      url = "https://storage.googleapis.com/uda_model/text/back_trans_checkpoints.zip"
      file_path = DownloadUtil.download(url, dest_dir=dest_dir)
      DownloadUtil.unzip(file_path)
  
file_path: nlpaug/nlpaug/util/file/download.py
imports: import gzip
  import os
  import shutil
  import tarfile
  import urllib
  import zipfile
  import gdown
  import requests
label_desc: Use image node_id 4 for calling the DownloadUtil obj's underlying member method code with example usage: obj.download_back_translation(dest_dir) without return types