code: def first_page(self):
          
          try:
              start_url = self.start_url
          except AttributeError:
              raise PageError("Page %r is already the first page" % self)
          return self.page_for_url(start_url)
docs: Return the first `Page` in the result sequence this `Page`
          instance is from.
  
          If the current page is already the first page in the sequence,
          calling this method raises a `ValueError`.