input: Write a function to remove all HTML tags from a given string. The function should return the cleaned string without any HTML tags.
  
  def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str
  
  # Test cases
  assert clean_html_tags("<p>This is a <b>test</b> string</p>") == "This is a test string"
  assert clean_html_tags("<div>Hello, World!</div>") == "Hello, World!"
  assert clean_html_tags("<a href='#'>Link</a>") == "Link"
  assert clean_html_tags("No tags in this string") == "No tags in this string"
  assert clean_html_tags("") == ""
output: def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str