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>Hello, <b>world</b>!</p>')
      'Hello, world!'
      >>> html_to_text('<a href="http://example.com">This is a link</a>')
      'This is a link'
      >>> html_to_text('No tags here.')
      'No tags here.'
      """
output:     import re
      return re.sub(r'<[^>]+>', '', html_string)