input: Write a function to clean a string of HTML tags and return the string without the tags. If the input string is empty, return an empty string.
  def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str
  
  assert clean_html_tags("<p>This is a <b>test</b> string</p>")=="This is a test string"
  assert clean_html_tags("<div>Another example</div>")=="Another example"
  assert clean_html_tags("<a href='link'>Link</a>")=="Link"
  assert clean_html_tags("<span>Text with tags</span>")=="Text with tags"
  assert clean_html_tags("")==""
output: def clean_html_tags(str):
      import re
      clean_str = re.sub("<.*?>", "", str)
      return clean_str