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Push application context in Flask

I am developing an online voting system for my final year college project . The multi threading class gives a user 15 seconds to vote . It accepts a timestamp cookie and compares it to the current time.
class MonitorThread(threading.Thread):
def __init__(self, timecookie):
threading.Thread.__init__(self)
self.timecookie = timecookie
def run(self):
try:
while 1:
timenow = datetime.timestamp(datetime.now())
if timenow - int(float(self.timecookie)) < 15:
continue
else:
return redirect(url_for('index'))
sleep(0.1)
except KeyboardInterrupt:
GPIO.cleanup()
The videostream route runs the user's webcam to capture images for face verification and also runs an instance of the multi threading class .
# app.route('/videostream')
def videostream():
video_stream = VideoCamera()
timecookie = getcookie('time')
MonitorThread(timecookie).start()
return Response(gen(video_stream), mimetype='multipart/x-mixed-replace; boundary=frame')
This results in an error:
Traceback (most recent call last):
File "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner
self.run()
File "/home/abhishek/Documents/sem8/project/myfinalyear/app/app.py", line 48, in run
return redirect(url_for('index'))
File "/home/abhishek/Documents/sem8/project/myfinalyear/env/lib/python3.8/site-packages/flask/helpers.py", line 306, in url_for
raise RuntimeError(
RuntimeError: Attempted to generate a URL without the application context being pushed. This has to be executed when application context is available.
I want to end the voting process as soon as the time is up . Please suggest ideas.

Have you tried wrapping it with a with statement?
with app.app_context():
If it still doesn't work, you can try setting a SERVER_NAME configuration, as written in the documentation:
If set, url_for can generate external URLs with only an application context instead of a request context

AWS lambda, scrapy and catching exceptions

I'm running scrapy as a AWS lambda function. Inside my function I need to have a timer to see whether it's running longer than 1 minute and if so, I need to run some logic. Here is my code:
def handler():
x = 60
watchdog = Watchdog(x)
try:
runner = CrawlerRunner()
runner.crawl(MySpider1)
runner.crawl(MySpider2)
d = runner.join()
d.addBoth(lambda _: reactor.stop())
reactor.run()
except Watchdog:
print('Timeout error: process takes longer than %s seconds.' % x)
# some other logic here
watchdog.stop()
Watchdog timer class I took from this answer. The problem is the code never hits that except Watchdog block, but rather throws an exception outside:
Exception in thread Thread-1:
Traceback (most recent call last):
File "/usr/lib/python3.6/threading.py", line 916, in _bootstrap_inner
self.run()
File "/usr/lib/python3.6/threading.py", line 1182, in run
self.function(*self.args, **self.kwargs)
File "./functions/python/my_scrapy/index.py", line 174, in defaultHandler
raise self
functions.python.my_scrapy.index.Watchdog: 1
I need to catch exception in the function. How would I go about that.
PS: I'm very new to Python.

Alright this question had me going a little crazy, here is why that doesn't work:
What the Watchdog object does is create another thread where the exception is raised but not handled (the exception is only handled in the main process). Luckily, twisted has some neat features.
You can do it running the reactor in another thread:
import time
from threading import Thread
from twisted.internet import reactor
runner = CrawlerRunner()
runner.crawl(MySpider1)
runner.crawl(MySpider2)
d = runner.join()
d.addBoth(lambda _: reactor.stop())
Thread(target=reactor.run, args=(False,)).start() # reactor will run in a different thread so it doesn't lock the script here
time.sleep(60) # Lock script here
# Now check if it's still scraping
if reactor.running:
# do something
else:
# do something else
I'm using python 3.7.0

Twisted has scheduling primitives. For example, this program runs for about 60 seconds:
from twisted.internet import reactor
reactor.callLater(60, reactor.stop)
reactor.run()

(Python) correct use of greenlets

I have a remotely installed BeagleBone Black that needs to control a measurement device, a pan/tilt head, upload measured data, host a telnet server,...
I'm using Python 2.7
This is the first project in which I need to program, so a lot of questions come up.
I'd mostly like to know if what I'm doing is a reasonable way of handling what I need and why certain things don't do what I think.
Certain modules need to work together and share data. Best example is the telnet module, when the telnet user requests the position of the pan/tilt head.
As I understand it, the server is blocking the program, so I use gevent/Greenlets to run it from the "main" script.
Stripped down versions:
teln module
from gevent import monkey; monkey.patch_all() # patch functions to use gevent
import gevent
import gevent.server
from telnetsrv.green import TelnetHandler, command
__all__ = ["MyTelnetHandler", "start_server"] # used when module is loaded as "from teln import *"
class MyTelnetHandler(TelnetHandler):
"""Telnet implementation."""
def writeerror(self, text):
"""Write errors in red, preceded by 'ERROR: '."""
TelnetHandler.writeerror(self, "\n\x1b[31;5;1mERROR: {}\x1b[0m\n".format(text))
#command(["exit", "logout", "quit"], hidden=True)
def dummy(self, params):
"""Disables these commands and get them out of the "help" listing."""
pass
def start_server():
"""Server constructor, starts server."""
server = gevent.server.StreamServer(("", 2323), MyTelnetHandler.streamserver_handle)
print("server created")
try:
server.serve_forever()
finally:
server.close()
print("server finished")
"""Main loop"""
if __name__ == "__main__":
start_server()
Main script:
#! /usr/bin/env python
# coding: utf-8
from gevent import monkey; monkey.patch_all() # patch functions to gevent versions
import gevent
from gevent import Greenlet
import teln # telnet handler
from time import sleep
from sys import exit
"""Main loop"""
if __name__ == "__main__":
thread_telnet = Greenlet(teln.start_server)
print("greenlet created")
thread_telnet.start()
print("started")
sleep(10)
print("done sleeping")
i = 1
try:
while not thread_telnet.ready():
print("loop running ({:03d})".format(i))
i += 1
sleep(1)
except KeyboardInterrupt:
print("interrupted")
thread_telnet.kill()
print("killed")
exit()
The final main loop would need to run much more functions.
questions:
Is this a reasonable way of running processes/functions at the same time?
How do I get a function in the telnet module to call functions from a third module, controlling the head?
How do I make sure that the head isn't being controlled by the telnet module as well as the main script (which runs some kind of schedule)?
In the "def start_server()" function in teln module, two print commands are called when starting and stopping the server. I do not see these appearing in the terminal. What could be happening?
When I open a telnet session from a remote machine, and then close it, I get the following output (program keeps running):
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/gevent/greenlet.py", line 536, in run
result = self._run(*self.args, **self.kwargs)
File "/usr/local/lib/python2.7/dist-packages/telnetsrv/telnetsrvlib.py", line 815, in inputcooker
c = self._inputcooker_getc()
File "/usr/local/lib/python2.7/dist-packages/telnetsrv/telnetsrvlib.py", line 776, in _inputcooker_getc
ret = self.sock.recv(20)
File "/usr/local/lib/python2.7/dist-packages/gevent/_socket2.py", line 283, in recv
self._wait(self._read_event)
File "/usr/local/lib/python2.7/dist-packages/gevent/_socket2.py", line 182, in _wait
self.hub.wait(watcher)
File "/usr/local/lib/python2.7/dist-packages/gevent/hub.py", line 651, in wait
result = waiter.get()
File "/usr/local/lib/python2.7/dist-packages/gevent/hub.py", line 898, in get
return self.hub.switch()
File "/usr/local/lib/python2.7/dist-packages/gevent/hub.py", line 630, in switch
return RawGreenlet.switch(self)
cancel_wait_ex: [Errno 9] File descriptor was closed in another greenlet
Fri Sep 22 09:31:12 2017 <Greenlet at 0xb6987bc0L: <bound method MyTelnetHandler.inputcooker of <teln.MyTelnetHandler instance at 0xb69a1c38>>> failed with cancel_wait_ex
While trying out different things to get to understand how greenlets work, I have received similar ("cancel_wait_ex: [Errno 9] File descriptor was closed in another greenlet") error messages often.
I have searched around but can't find/understand what is happening and what I am supposed to do.
If something goes wrong while running a greenlet, I do not get the exception that points to the problem (for instance when I try to print an integer), but a similar error message as above. How can I see the "original" raised exception?

Running several ApplicationSessions non-blockingly using autbahn.asyncio.wamp

I'm trying to run two autobahn.asyncio.wamp.ApplicationSessions in python at the same time. Previously, I did this using a modification of the autobahn library as suggested in this post's answer. I now
require a bit more professional solution.
After googling about for a while, this post appeared quite promising, but uses the twisted library, instead of asyncio. I wasn't able to identify a similar solution for the asyncio branch of the autobahn library, since it doesn't appear to be using Reactors.
The main problem I have, is that ApplicationRunner.run() is blocking (which is why I previously outsourced it to a thread), so I can't just run a second ApplicationRunner after it.
I do need to access 2 websocket channels at the same time, which I cannot appear to do with a single ApplicationSession.
My Code so far:
from autobahn.asyncio.wamp import ApplicationSession
from autobahn.asyncio.wamp import ApplicationRunner
from asyncio import coroutine
import time
channel1 = 'BTC_LTC'
channel2 = 'BTC_XMR'
class LTCComponent(ApplicationSession):
def onConnect(self):
self.join(self.config.realm)
#coroutine
def onJoin(self, details):
def onTicker(*args, **kwargs):
print('LTCComponent', args, kwargs)
try:
yield from self.subscribe(onTicker, channel1)
except Exception as e:
print("Could not subscribe to topic:", e)
class XMRComponent(ApplicationSession):
def onConnect(self):
self.join(self.config.realm)
#coroutine
def onJoin(self, details):
def onTicker(*args, **kwargs):
print('XMRComponent', args, kwargs)
try:
yield from self.subscribe(onTicker, channel2)
except Exception as e:
print("Could not subscribe to topic:", e)
def main():
runner = ApplicationRunner("wss://api.poloniex.com:443", "realm1", extra={})
runner.run(LTCComponent)
runner.run(XMRComponent) # <- is not being called
if __name__ == "__main__":
try:
main()
except KeyboardInterrupt:
quit()
except Exception as e:
print(time.time(), e)
My knowledge of the autobahn library is limited, and I'm afraid the documentation isn't improving my situation much. Am I overlooking something here? A function, a parameter, which would enable me to either compound my components or run them both at once?
Perhaps a similar solution as provided here, which implements an alternative ApplicationRunner ?
Related Topics
Running two ApplicationSessions in twisted
Running Autobahn ApplicationRunner in Thread
Autobahn.wamp.ApplicationSession Source
Autobahn.wamp.Applicationrunner Source
As Requested, the Traceback from #stovfl's answer using multithreading code:
Exception in thread Thread-2:
Traceback (most recent call last):
File "/home/nils/anaconda3/lib/python3.5/threading.py", line 914, in _bootstrap_inner
self.run()
File "/home/nils/git/tools/gemini_wss/t2.py", line 27, in run
self.appRunner.run(self.__ApplicationSession)
File "/home/nils/anaconda3/lib/python3.5/site-packages/autobahn- 0.14.1-py3.5.egg/autobahn/asyncio/wamp.py", line 143, in run
transport_factory = WampWebSocketClientFactory(create, url=self.url, serializers=self.serializers)
File "/home/nils/anaconda3/lib/python3.5/site-packages/autobahn- 0.14.1-py3.5.egg/autobahn/asyncio/websocket.py", line 319, in __init__
WebSocketClientFactory.__init__(self, *args, **kwargs)
File "/home/nils/anaconda3/lib/python3.5/site-packages/autobahn- 0.14.1-py3.5.egg/autobahn/asyncio/websocket.py", line 268, in __init__
self.loop = loop or asyncio.get_event_loop()
File "/home/nils/anaconda3/lib/python3.5/asyncio/events.py", line 626, in get_event_loop
return get_event_loop_policy().get_event_loop()
File "/home/nils/anaconda3/lib/python3.5/asyncio/events.py", line 572, in get_event_loop
% threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'Thread-2'.
Exception in thread Thread-1:
**Same as in Thread-2**
...
RuntimeError: There is no current event loop in thread 'Thread-1'.

As I see from the traceback, we only reach Step 2 of 4
From the asyncio docs:
This module provides infrastructure for writing single-threaded concurrent code using coroutines, multiplexing I/O access over sockets and other resources
So I drop my first proposal using multithreading.
I could imagin the following three options:
Do it with multiprocessing instead of multithreading
Do it with coroutine inside asyncio loop
Switch between channels in def onJoin(self, details)
Second proposal, first option using multiprocessing.
I can start two asyncio loops, so appRunner.run(...) should work.
You can use one class ApplicationSession if the channel are the only different.
If you need to pass different class ApplicationSession add it to the args=
class __ApplicationSession(ApplicationSession):
# ...
try:
yield from self.subscribe(onTicker, self.config.extra['channel'])
except Exception as e:
# ...
import multiprocessing as mp
import time
def ApplicationRunner_process(realm, channel):
appRunner = ApplicationRunner("wss://api.poloniex.com:443", realm, extra={'channel': channel})
appRunner.run(__ApplicationSession)
if __name__ == "__main__":
AppRun = [{'process':None, 'channel':'BTC_LTC'},
{'process': None, 'channel': 'BTC_XMR'}]
for app in AppRun:
app['process'] = mp.Process(target = ApplicationRunner_process, args = ('realm1', app['channel'] ))
app['process'].start()
time.sleep(0.1)
AppRun[0]['process'].join()
AppRun[1]['process'].join()

Following the approach you linked for twisted I managed to get same behaviour with asyncio setting start_loop=False
import asyncio
from autobahn.asyncio.wamp import ApplicationSession, ApplicationRunner
runner1 = ApplicationRunner(url, realm, extra={'cli_id': 1})
coro1 = runner1.run(MyApplicationSession, start_loop=False)
runner2 = ApplicationRunner(url, realm, extra={'cli_id': 2})
coro2 = runner2.run(MyApplicationSession, start_loop=False)
asyncio.get_event_loop().run_until_complete(coro1)
asyncio.get_event_loop().run_until_complete(coro2)
asyncio.get_event_loop().run_forever()
class MyApplicationSession(ApplicationSession):
def __init__(self, cfg):
super().__init__(cfg)
self.cli_id = cfg.extra['cli_id']
def onJoin(self, details):
print("session attached", self.cli_id)

Python Multiprocessing atexit Error "Error in atexit._run_exitfuncs"

I am trying to run a simple multiple processes application in Python. The main thread spawns 1 to N processes and waits until they all done processing. The processes each run an infinite loop, so they can potentially run forever without some user interruption, so I put in some code to handle a KeyboardInterrupt:
#!/usr/bin/env python
import sys
import time
from multiprocessing import Process
def main():
# Set up inputs..
# Spawn processes
Proc( 1).start()
Proc( 2).start()
class Proc ( Process ):
def __init__ ( self, procNum):
self.id = procNum
Process.__init__(self)
def run ( self ):
doneWork = False
while True:
try:
# Do work...
time.sleep(1)
sys.stdout.write('.')
if doneWork:
print "PROC#" + str(self.id) + " Done."
break
except KeyboardInterrupt:
print "User aborted."
sys.exit()
# Main Entry
if __name__=="__main__":
main()
The problem is that when using CTRL-C to exit, I get an additional error even though the processes seem to exit immediately:
......User aborted.
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
File "C:\Python26\lib\atexit.py", line 24, in _run_exitfuncs
func(*targs, **kargs)
File "C:\Python26\lib\multiprocessing\util.py", line 281, in _exit_function
p.join()
File "C:\Python26\lib\multiprocessing\process.py", line 119, in join
res = self._popen.wait(timeout)
File "C:\Python26\lib\multiprocessing\forking.py", line 259, in wait
res = _subprocess.WaitForSingleObject(int(self._handle), msecs)
KeyboardInterrupt
Error in sys.exitfunc:
Traceback (most recent call last):
File "C:\Python26\lib\atexit.py", line 24, in _run_exitfuncs
func(*targs, **kargs)
File "C:\Python26\lib\multiprocessing\util.py", line 281, in _exit_function
p.join()
File "C:\Python26\lib\multiprocessing\process.py", line 119, in join
res = self._popen.wait(timeout)
File "C:\Python26\lib\multiprocessing\forking.py", line 259, in wait
res = _subprocess.WaitForSingleObject(int(self._handle), msecs)
KeyboardInterrupt
I am running Python 2.6 on Windows. If there is a better way to handle multiprocessing in Python, please let me know.

This is a very old question, but it seems like the accepted answer does not actually fix the problem.
The main issue is that you need to handle the keyboard interrupt in the parent process as well. Additionally to that, in the while loop, you just need to exit the loop, there's no need to call sys.exit()
I've tried to as closely match the example in the original question. The doneWork code does nothing in the example so have removed that for clarity.
import sys
import time
from multiprocessing import Process
def main():
# Set up inputs..
# Spawn processes
try:
processes = [Proc(1), Proc(2)]
[p.start() for p in processes]
[p.join() for p in processes]
except KeyboardInterrupt:
pass
class Proc(Process):
def __init__(self, procNum):
self.id = procNum
Process.__init__(self)
def run(self):
while True:
try:
# Do work...
time.sleep(1)
sys.stdout.write('.')
except KeyboardInterrupt:
print("User aborted.")
break
# Main Entry
if __name__ == "__main__":
main()

Rather then just forcing sys.exit(), you want to send a signal to your threads to tell them to stop. Look into using signal handlers and threads in Python.
You could potentially do this by changing your while True: loop to be while keep_processing: where keep_processing is some sort of global variable that gets set on the KeyboardInterrupt exception. I don't think this is a good practice though.