text: from books import BookDict
  from typing import TYPE_CHECKING
  
  def demo() -> None:  # <1>
      book = BookDict(  # <2>
          isbn='0134757599',
          title='Refactoring, 2e',
          authors=['Martin Fowler', 'Kent Beck'],
          pagecount=478
      )
      authors = book['authors'] # <3>
      if TYPE_CHECKING:  # <4>
          reveal_type(authors)  # <5>
      authors = 'Bob'  # <6>
      book['weight'] = 4.2
      del book['title']
  
  
  if __name__ == '__main__':
      demo()
  