[Python][Tornado]: 500 Internal Server Error when navigating between pages - html

Question

I'm trying to navigate between 2 HTML pages through Tornado. Following is the code for the routes and their respective handlers:
class MainHandler(tornado.web.RequestHandler):
def get(self):
log.info("Rendering index.html")
self.render("index.html")
class NotificationsPageHandler(tornado.web.RequestHandler):
def get(self):
log.info("Rendering notifications")
self.render("notifications.html")
def start_server():
settings = {
"static_path": os.path.join(os.path.dirname(__file__), "static")
}
application = tornado.web.Application([
(r"/", MainHandler),
(r"/notifications.html", NotificationsPageHandler),
], **settings)
application.listen(8989)
tornado.ioloop.IOLoop.current().start()
When I load 127.0.0.1:8989 on the browser, I get the index.html page but when I try to navigate to notifications.html through an anchor tag in index.html, I get the following stack trace:
2016-07-06 12:07:06,546 - tornado.application - ERROR - Uncaught exception GET /notifications.html (127.0.0.1)
HTTPServerRequest(protocol='http', host='127.0.0.1:8989', method='GET', uri='/notifications.html', version='HTTP/1.1', remote_ip='127.0.0.1', headers={'Accept-Language': 'en-US,en;q=0.8', 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8', 'Host': '127.0.0.1:8989', 'Upgrade-Insecure-Requests': '1', 'Accept-Encoding': 'gzip, deflate, sdch', 'User-Agent': 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36', 'Referer': 'http://127.0.0.1:8989/', 'Connection': 'keep-alive'})
Traceback (most recent call last):
File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 1443, in _execute
result = method(*self.path_args, **self.path_kwargs)
File "BADWebServer.py", line 231, in get
self.render("notifications.html")
File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 699, in render
html = self.render_string(template_name, **kwargs)
File "/usr/local/lib/python3.5/dist-packages/tornado/web.py", line 806, in render_string
return t.generate(**namespace)
File "/usr/local/lib/python3.5/dist-packages/tornado/template.py", line 345, in generate
return execute()
File "notifications_html.generated.py", line 5, in _tt_execute
_tt_tmp = item.score # notifications.html:37
NameError: name 'item' is not defined
2016-07-06 12:07:06,548 - tornado.access - ERROR - 500 GET /notifications.html (127.0.0.1) 4.51ms
I have seen a similar post, how to navigate from one html to other in tornado using anchor tag but I'm not sure why I'm getting the exception.

Answer 1

You're getting the error because, as the trace says, "name 'item' is not defined". Your notifications.html template contains some markup like:
{{ item.score }}
... but you haven't passed an "item" variable in. See the template syntax guide for an example.