How to schedule a function to run every hour on Flask

Question

I have a Flask web hosting with no access to cron command   How can I execute some Python function every hour

User · Answer

A complete example using schedule and multiprocessing, with on and off control and parameter to run_job() the return codes are simplified and interval is set to 10sec, change to every(2).hour.do()for 2hours. Schedule is quite impressive it does not drift and I've never seen it more than 100ms off when scheduling. Using multiprocessing instead of threading because it has a termination method.

#!/usr/bin/env python3

import schedule
import time
import datetime
import uuid

from flask import Flask, request
from multiprocessing import Process

app = Flask(__name__)
t = None
job_timer = None

def run_job(id):
    """ sample job with parameter """
    global job_timer
    print("timer job id={}".format(id))
    print("timer: {:.4f}sec".format(time.time() - job_timer))
    job_timer = time.time()

def run_schedule():
    """ infinite loop for schedule """
    global job_timer
    job_timer = time.time()
    while 1:
        schedule.run_pending()
        time.sleep(1)

@app.route('/timer/<string:status>')
def mytimer(status, nsec=10):
    global t, job_timer
    if status=='on' and not t:
        schedule.every(nsec).seconds.do(run_job, str(uuid.uuid4()))
        t = Process(target=run_schedule)
        t.start()
        return "timer on with interval:{}sec\n".format(nsec)
    elif status=='off' and t:
        if t:
            t.terminate()
            t = None
            schedule.clear()
        return "timer off\n"
    return "timer status not changed\n"

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

You test this by just issuing:

$ curl http://127.0.0.1:5000/timer/on
timer on with interval:10sec
$ curl http://127.0.0.1:5000/timer/on
timer status not changed
$ curl http://127.0.0.1:5000/timer/off
timer off
$ curl http://127.0.0.1:5000/timer/off
timer status not changed

Every 10sec the timer is on it will issue a timer message to console:

127.0.0.1 - - [18/Sep/2018 21:20:14] "GET /timer/on HTTP/1.1" 200 -
timer job id=b64ed165-911f-4b47-beed-0d023ead0a33
timer: 10.0117sec
timer job id=b64ed165-911f-4b47-beed-0d023ead0a33
timer: 10.0102sec

User · Answer

For a simple solution  you could add a route such as   app route   cron do the thing   methods   POST    def do the thing        logging info  Did the thing       return  OK   200   Then add a unix cron job that POSTs to this endpoint periodically  For example to run it once a minute  in terminal type crontab -e and add this line              opt local bin curl -X POST https   YOUR APP cron do the thing    Note that the path to curl has to be complete  as when the job runs it won t have your PATH  You can find out the full path to curl on your system by which curl   I like this in that it s easy to test the job manually  it has no extra dependencies and as there isn t anything special going on it is easy to understand   Security  If you d like to password protect your cron job  you can pip install Flask-BasicAuth  and then add the credentials to your app configuration   app   Flask   name    app config  BASIC AUTH REALM      realm  app config  BASIC AUTH USERNAME      falken  app config  BASIC AUTH PASSWORD      joshua    To password protect the job endpoint   from flask basicauth import BasicAuth basic auth   BasicAuth app    app route   cron do the thing   methods   POST     basic auth required def do the thing        logging info  Did the thing a bit more securely       return  OK   200   Then to call it from your cron job              opt local bin curl -X POST https   falken joshua YOUR APP cron do the thing

User · Answer

Another alternative might be to use Flask-APScheduler which plays nicely with Flask  e g     Loads scheduler configuration from Flask configuration   Loads job definitions from Flask configuration   More information here    https   pypi python org pypi Flask-APScheduler

User · Answer

I ve tried using flask instead of a simple apscheduler what you need to install is  pip3 install flask apscheduler  Below is the sample of my code  from flask import Flask from flask apscheduler import APScheduler  app   Flask   name    scheduler   APScheduler    def scheduleTask        print  quot This test runs every 3 seconds quot    if   name         main         scheduler add job id    Scheduled Task   func scheduleTask  trigger  quot interval quot   seconds 3      scheduler start       app run host  quot 0 0 0 0 quot

User · Answer

You may use flask-crontab module  which is quite easy  Step 1  pip install flask-crontab Step 2  from flask import Flask from flask crontab import Crontab  app   Flask   name    crontab   Crontab app   Step 3   crontab job minute  quot 0 quot   hour  quot 6 quot   day  quot   quot   month  quot   quot   day of week  quot   quot   def my scheduled job        do something    Step 4  On cmd  hit flask crontab add  Done  now simply run your flask application  and you can check your function will call at 6 00 every day  You may take reference from Here  Official DOc

User · Answer

You can use BackgroundScheduler   from APScheduler package  v3 5 3    import time import atexit  from apscheduler schedulers background import BackgroundScheduler   def print date time        print time strftime   A   d   B  Y  I  M  S  p      scheduler   BackgroundScheduler   scheduler add job func print date time  trigger  interval   seconds 3  scheduler start      Shut down the scheduler when exiting the app atexit register lambda  scheduler shutdown      Note that two of these schedulers will be launched when Flask is in debug mode  For more information  check out this question

User · Answer

I m a little bit new with the concept of application schedulers  but what I found here for APScheduler v3 3 1   it s something a little bit different  I believe that for the newest versions  the package structure  class names  etc   have changed  so I m putting here a fresh solution which I made recently  integrated with a basic Flask application     usr bin python3  quot  quot  quot  Demonstrating Flask  using APScheduler   quot  quot  quot   from apscheduler schedulers background import BackgroundScheduler from flask import Flask  def sensor         quot  quot  quot  Function for test purposes   quot  quot  quot      print  quot Scheduler is alive  quot    sched   BackgroundScheduler daemon True  sched add job sensor  interval  minutes 60  sched start    app   Flask   name      app route  quot  home quot   def home         quot  quot  quot  Function for test purposes   quot  quot  quot      return  quot Welcome Home      quot   if   name       quot   main   quot       app run    I m also leaving this Gist here  if anyone have interest on updates for this example  Here are some references  for future readings   APScheduler Doc  https   apscheduler readthedocs io en latest  daemon True  https   docs python org 3 4 library threading html thread-objects

User · Answer

You could make use of APScheduler in your Flask application and run your jobs via its interface   import atexit    v2 x version - see https   stackoverflow com a 38501429 135978   for the 3 x version from apscheduler scheduler import Scheduler from flask import Flask  app   Flask   name     cron   Scheduler daemon True    Explicitly kick off the background thread cron start     cron interval schedule hours 1  def job function          Do your work here     Shutdown your cron thread if the web process is stopped atexit register lambda  cron shutdown wait False    if   name         main         app run

User · Answer

You could try using APScheduler s BackgroundScheduler to integrate interval job into your Flask app  Below is the example that uses blueprint and app factory  init py     from datetime import datetime    import BackgroundScheduler from apscheduler schedulers background import BackgroundScheduler from flask import Flask  from webapp models main import db  from webapp controllers main import main blueprint        define the job def hello job        print  Hello Job  The time is   s    datetime now     def create app object name       app   Flask   name        app config from object object name      db init app app      app register blueprint main blueprint        init BackgroundScheduler job     scheduler   BackgroundScheduler         in your case you could change seconds to hours     scheduler add job hello job  trigger  interval   seconds 3      scheduler start        try            To keep the main thread alive         return app     except            shutdown if app occurs except          scheduler shutdown     Hope it helps     Ref      https   github com agronholm apscheduler blob master examples schedulers background py

User · Answer

You might want to use some queue mechanism with scheduler like RQ scheduler or something more heavy like Celery  most probably an overkill

[python] How to schedule a function to run every hour on Flask?

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