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``

def activate_page(self, page_id):
        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``

        """
        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))