docs: def download_command(args):
      """Downloads and extracts the latest App Engine SDK to the given
      destination."""
      latest_two_versions = list(reversed(get_gae_versions()))[:2]
  
      zip = None
      version_number = None
  
      for version in latest_two_versions:
          if is_existing_up_to_date(args.destination, version[0]):
              print(
                  'App Engine SDK already exists and is up to date '
                  'at {}.'.format(args.destination))
              return
  
          try:
              print('Downloading App Engine SDK {}'.format(
                  '.'.join([str(x) for x in version[0]])))
              zip = download_sdk(version[1])
              version_number = version[0]
              break
          except Exception as e:
              print('Failed to download: {}'.format(e))
              continue
  
      if not zip:
          return
  
      print('Extracting SDK to {}'.format(args.destination))
  
      extract_zip(zip, args.destination)
      fixup_version(args.destination, version_number)
  
      print('App Engine SDK installed.')