input: def clean_html_tags(str: str) -> str:
      """
      Clean a string of HTML tags.
      >>> clean_html_tags("<p>This is a <b>test</b> string</p>")
      'This is a test string'
      >>> clean_html_tags("<html><head><title>Test</title></head><body>Hello <b>World</b>!</body></html>")
      'Hello World!'
      """
output:     import re
      clean_text = re.sub(r'<.*?>', '', str)
      return clean_text