code: def url_to_filename(url: str, etag: str = None) -> str:
      
      url_bytes = url.encode('utf-8')
      b64_bytes = base64.b64encode(url_bytes)
      decoded = b64_bytes.decode('utf-8')
  
      if etag:
          # Remove quotes from etag
          etag = etag.replace('"', '')
          return f"{decoded}.{etag}"
      else:
          return decoded
docs: Converts a url into a filename in a reversible way.
      If `etag` is specified, add it on the end, separated by a period
      (which necessarily won't appear in the base64-encoded filename).
      Get rid of the quotes in the etag, since Windows doesn't like them.