code: def download_ftp_url(source_url, target_uri, buffer_size=8192):
      
  
      ensure_file_directory(target_uri)
  
      with urllib.request.urlopen(source_url) as source_file:
          with open(target_uri, 'wb') as target_file:
              shutil.copyfileobj(source_file, target_file, buffer_size)
docs: Uses urllib. thread safe?