Flask throwing 'Working outside of request context.' - flask

Question

I am trying to use celery for my app which is made in flask but I get the following error "Working outside of request context". It sounds like I am trying to access a request object before the front end makes a request, but I cannot figure out what is wrong. I appreciate if you can let me know what is the problem.
[2017-04-26 13:33:04,940: INFO/MainProcess] Received task: app.result[139a2679-e9df-49b9-ab42-1f53a09c01fd]
[2017-04-26 13:33:06,168: ERROR/PoolWorker-2] Task app.result[139a2679-e9df-49b9-ab42-1f53a09c01fd] raised unexpected: RuntimeError('Working outside of request context.\n\nThis typically means that you attempted to use functionality that needed\nan active HTTP request. Consult the documentation on testing for\ninformation about how to avoid this problem.',)
Traceback (most recent call last):
File "/Library/Python/2.7/site-packages/celery/app/trace.py", line 367, in trace_task
R = retval = fun(*args, **kwargs)
File "/Users/Pooneh/projects/applications/ray_tracer_app_flask/flask_celery.py", line 14, in __call__
return TaskBase.__call__(self, *args, **kwargs)
File "/Library/Python/2.7/site-packages/celery/app/trace.py", line 622, in __protected_call__
return self.run(*args, **kwargs)
File "/Users/Pooneh/projects/applications/ray_tracer_app_flask/app.py", line 33, in final_result
light_position = request.args.get("light_position", "(0, 0, 0)", type=str)
File "/Library/Python/2.7/site-packages/werkzeug/local.py", line 343, in __getattr__
return getattr(self._get_current_object(), name)
File "/Library/Python/2.7/site-packages/werkzeug/local.py", line 302, in _get_current_object
return self.__local()
File "/Library/Python/2.7/site-packages/flask/globals.py", line 37, in _lookup_req_object
raise RuntimeError(_request_ctx_err_msg)
RuntimeError: Working outside of request context.
This typically means that you attempted to use functionality that needed
an active HTTP request. Consult the documentation on testing for
information about how to avoid this problem.
app.py
app = Flask(__name__)
app.config.update(CELERY_BROKER_URL = 'amqp://localhost//',
CELERY_RESULT_BACKEND='amqp://localhost//')
celery = make_celery(app)
#app.route('/')
def my_form():
return render_template("form.html")
#app.route('/result')
def result():
final_result.delay()
return "celery!"
#celery.task(name='app.result')
def final_result():
light_position = request.args.get("light_position", "(0, 0, 0)", type=str)
light_position_coor = re.findall("[-+]?\d*\.\d+|[-+]?\d+", light_position)
x = float(light_position_coor[0])
y = float(light_position_coor[1])
z = float(light_position_coor[2])
encoded = base64.b64encode(open("/Users/payande/projects/applications/app_flask/static/pic.png", "rb").read())
return jsonify(data=encoded)

Answer 1

Celery tasks are run by a background worker asynchronously outside of the HTTP request (which is one of they main benefits of using them), so you cannot access the request object within the task.
You could pass the data to the task as arguments instead:
final_result.delay(request.args.get("light_position"))
#celery.task(name='app.result')
def final_result(light_position):
...
Of course this also means that the return value of the task cannot be used in a HTTP response (since the task can complete after the response has been already sent).