def linkify(words, urls):
  if isinstance(words, basestring) or not isinstance(words, (list, tuple)):
    if isinstance(urls, basestring) or not isinstance(urls, (list, tuple)):
      return linkify([words], [urls])
    else:
      return words
  else:
    html_links = ['<a href="{1}">{0}</a>'.format(word,url)
                    for word, url in zip(words, urls)
                      if word is not None and url is not None]
    return ", ".join(html_links)