input: Write a function to remove all HTML tags from a given string. If the input string is empty then return the empty string. If the input string does not contain any HTML tags, return the string as is.
  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("<p>This is another <i>test</i> string</p>")=="This is another test string"
  assert clean_html_tags("No tags here")=="No tags here"
  assert clean_html_tags("")==""
  assert clean_html_tags("<p>Only one tag</p>")=="Only one tag"
output: def clean_html_tags(str):
      import re
      clean_str = re.sub("<.*?>", "", str)
      return clean_str