input: Write a function to remove all HTML tags from a given string. The function should return the cleaned string without any HTML tags.
  
  import re
  
  # Clean a string of HTML tags
  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><span>Hello</span> World</div>") == "Hello World"
  assert clean_html_tags("") == ""
  assert clean_html_tags("<a href='#'>Link</a>") == "Link"
  assert clean_html_tags("No tags here") == "No tags here"
output: def clean_html_tags(str):
      clean_str = re.sub("<.*?>", "", str)
      return clean_str