class_docstr: Helper function for downloading external dependency
  
  >>> from nlpaug.util.file.download import DownloadUtil
code: def download(src, dest_dir, dest_file=None):
      if not os.path.exists(dest_dir):
          os.makedirs(dest_dir)
  
      if dest_file is None:
          dest_file = os.path.basename(src)
  
      if not os.path.exists(dest_dir + dest_file):
          req = urllib.request.Request(src)
          file = urllib.request.urlopen(req)
          with open(os.path.join(dest_dir, dest_file), "wb") as output:
              output.write(file.read())
      return os.path.join(dest_dir, dest_file)
  
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 5 for calling the DownloadUtil obj's underlying member method code with example usage: obj.download(src, dest_dir, dest_file) and returns: os