input: Write a function to clean a string of HTML tags using regular expressions. The function should remove all HTML tags and return the cleaned string.
  def clean_html_tags(html_str):
      clean_str = re.sub("<.*?>", "", html_str)
      return clean_str
output: def clean_html_tags(html_str):
      clean_str = re.sub("<.*?>", "", html_str)
      return clean_str