code: def activate_page(self, page_id):
          r
          if page_id == "next":
              page_keys = list(self._pages.keys())
              key_count = len(page_keys)
              if key_count > 0:
                  idx = page_keys.index(self._active_page.page_id)
                  if idx >= key_count-1:
                      idx = 0
                  else:
                      idx += 1
                  self._active_page = self._pages[page_keys[idx]]
                  self._active_page._render()
                  self._page_changed(self._active_page)
  
          elif page_id in self._pages:
              self._active_page = self._pages[page_id]
              self._page_changed(self._active_page)
          else:
              raise ValueError("Page with {page_id} not found in page list".format(page_id = page_id))
docs: r"""
          Activates a display page. Content of the active page is shown in the display.
  
          :param page_id:  Id of page to activate
          :type page_id: ``str``