input: 
  def html_to_text(html_string: str) -> str:
      """Convert an HTML string to plain text by removing all HTML tags.
      >>> html_to_text('<p>This <b>is</b> a test.</p>')
      'This is a test.'
      >>> html_to_text('<html><body><h1>Title</h1><p>Paragraph text</p></body></html>')
      'TitleParagraph text'
      """
  
output:     import re
      return re.sub(r'<[^>]+>', '', html_string)