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##########################
Frequently Asked Questions
##########################
Why doesn't the scheduler run my jobs?
======================================
This could be caused by a number of things. The two most common issues are:
#. Running the scheduler inside a uWSGI worker process while threads have not been
enabled (see the next section for this)
#. Starting a synchronous scheduler with
:meth:`~apscheduler.schedulers.sync.Scheduler.start_in_background` and then letting
the execution reach the end of the script
To demonstrate the latter case, a script like this will **not work**::
from apscheduler.schedulers.sync import Scheduler
from apscheduler.schedulers.triggers.cron import CronTrigger
def mytask():
print("hello")
scheduler = Scheduler()
scheduler.start_in_background()
scheduler.add_schedule(mytask, CronTrigger(hour=0))
The script above will **exit** right after calling
:meth:`~apscheduler.schedulers.sync.add_schedule` so the scheduler will not have a
chance to run the scheduled task.
If you're having any other issue, then enabling debug logging as instructed in the
:ref:`troubleshooting` section should shed some light into the problem.
Why am I getting a ValueError?
==============================
If you're receiving an error like the following::
ValueError: This Job cannot be serialized since the reference to its callable (<bound method xxxxxxxx.on_crn_field_submission
of <__main__.xxxxxxx object at xxxxxxxxxxxxx>>) could not be determined. Consider giving a textual reference (module:function
name) instead.
This means that the function you are attempting to schedule has one of the following
problems:
* It is a lambda function (e.g. ``lambda x: x + 1``)
* It is a bound method (function tied to a particular instance of some class)
* It is a nested function (function inside another function)
* You are trying to schedule a function that is not tied to any actual module (such as a
function defined in the REPL, hence ``__main__`` as the module name)
In these cases, it is impossible for the scheduler to determine a "lookup path" to find
that specific function instance in situations where, for example, the scheduler process
is restarted, or a process pool worker is being sent the related job object.
Common workarounds for these problems include:
* Converting a lambda to a regular function
* Moving a nested function to the module level or to class level as either a class
method or a static method
* In case of a bound method, passing the unbound version (``YourClass.method_name``) as
the target function to ``add_job()`` with the class instance as the first argument (so
it gets passed as the ``self`` argument)
Is there a graphical user interface for APScheduler?
====================================================
No graphical interface is provided by the library itself. However, there are some third
party implementations, but APScheduler developers are not responsible for them. Here is
a potentially incomplete list:
* django_apscheduler_
* apschedulerweb_
* `Nextdoor scheduler`_
.. warning:: As of this writing, these third party offerings have not been updated to
work with APScheduler 4.
.. _django_apscheduler: https://pypi.org/project/django-apscheduler/
.. _Flask-APScheduler: https://pypi.org/project/flask-apscheduler/
.. _pyramid_scheduler: https://github.com/cadithealth/pyramid_scheduler
.. _aiohttp: https://pypi.org/project/aiohttp/
.. _apschedulerweb: https://github.com/marwinxxii/apschedulerweb
.. _Nextdoor scheduler: https://github.com/Nextdoor/ndscheduler
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