How to handle threading expetion in tornado? - python-3.x

Question

I am working with white board application. When I load the page first time it gives the perfect output and second time also gives the perfect output. But when I refresh the page third time it gives the below error as shown below,
Exception in thread Thread-3:
Traceback (most recent call last):
File "/usr/lib/python3.2/threading.py", line 740, in _bootstrap_inner
self.run()
File "/usr/lib/python3.2/threading.py", line 693, in run
self._target(*self._args, **self._kwargs)
File "/home/nyros/Desktop/python3/whiteboard/websockethandler.py", line 45, in redis_listener
listener.send_message(message['data'])
File "/home/nyros/Desktop/python3/whiteboard/websockethandler.py", line 150, in send_message
self.write_message(message)
File "/home/nyros/Desktop/python3/venv3/lib/python3.2/site-packages/tornado/websocket.py", line 165, in write_message
self.ws_connection.write_message(message, binary=binary)
AttributeError: 'NoneType' object has no attribute 'write_message'
Code As below:
def redis_listener(self, room_name, page_no):
self.logger.info("Starting listener thread for room %s" % room_name)
rr = redis.Redis(host=config.REDIS_IP_ADDRESS, port=config.REDIS_PORT, db=1)
r = rr.pubsub()
r.subscribe(self.construct_key(room_name, page_no))
for message in r.listen():
print(message, "ok ok ok .......")
for listener in self.application.LISTENERS.get(room_name, {}).get(page_no, []):
self.logger.debug("Sending message to room %s" % room_name)
listener.send_message(message['data'])
def send_message(self, message):
if type(message) == type(b''):
self.logger.info("Decoding binary string")
message = message.decode('utf-8')
elif type(message) != type(''):
self.logger.info("Converting message from %s to %s" % (type(message),
type('')))
message = str(message)
message = b64encode(compress(bytes(quote(message), 'utf-8'), 9))
self.write_message(message)

Answer 1

Looks like you have different listeners in array. It's hard to tell exact reason of problem, but try to log them like this:
if hasattr(self, 'write_message'):
self.write_message(message)
else:
self.logger.debug(self)
It will prevent error.