Periodically lets you define periodic tasks in Python, and then run them however you want (think cron job).

Goals

1. Tasks and their schedules should be defined in Python—not crontabs or the database.
2. There should be multiple ways to trigger tasks, but only one syntax for defining them. Just because you trigger your tasks with a cron job on one server doesn't mean you can always do that. When you can't, you shouldn't have to rewrite all your code—just change a setting.
3. The system should be highly flexible, but…
4. …there should be shortcuts for the most common schedules (hourly, daily, etc.).
5. The system should try to recover gracefully, but…
6. …it should also alert the administrators if anything goes wrong.

Installation

1. pip install django-periodically
2. Add 'periodically' to your INSTALLED_APPS in settings.py.
3. python manage.py syncdb

Usage

Defining and Scheduling Tasks

Periodically gives you a few ways to schedule periodic tasks. The easiest is to use the included decorators:

from periodically.decorators import *

@hourly()
def my_task():
    print 'Do something!'

@every(minutes=45)
def my_other_task():
    print 'Do something else every 45 minutes!'

However, you can also define task classes:

from periodically.tasks import PeriodicTask
from periodically import register
from periodically.schedules import Daily

# Define the task.
class MyTask(PeriodicTask):
    def run(self):
        print 'Do something.'

# Schedule the task.
register.task(MyTask(), Daily())

Tasks can be scheduled anywhere in your project, but Periodically automatically looks for a periodictasks module in your INSTALLED_APPS, so it's probably a good idea to define all your tasks in myapp/periodictasks.py.

Running Your Tasks

Periodically uses a pluggable backend system to decouple the defining and scheduling of your tasks from their execution. The default backend will not run your tasks automatically, so you need to tell it to by using the runtasks management command. Generally, you would use a cronjob (or similar) to do this. For example, placing the following line in your crontab file would check for tasks that need to be run every five minutes:

*/5 * * * * python /path/to/manage.py runtasks

### Scheduler Backends

One of the things that makes Periodically so flexible is its scheduler backend system. A single project can even use multiple backends!

Using Custom Backends

In settings.py:

PERIODICALLY = {
        ...
    'SCHEDULERS': {
    'special': {
        'backend': 'myapp.MySpecialBackend',
        },
    },
}

Then, in your app's periodictasks.py file:

@hourly(backend='special')
def do_something():
            print 'Doing something!'

This setup works great for scheduling a specific task with a particular backend, but if you find that you want to change the backend that all of your tasks use, it's easier to just override the default:

PERIODICALLY = {
    ...
    'SCHEDULERS': {
        'default': {
            'backend': 'myapp.MySpecialBackend',
        },
    },
}

With the above code in your settings.py file, all tasks will use myapp.MySpecialBackend by default.

Backend Groups

Sometimes it's convenient to create backend groups. A good example of this is when you have several different backends that should all be triggered by a cron job. Here's how you add backends to groups in your settings.py file:

PERIODICALLY = {
        ...
    'SCHEDULERS': {
                'default': {
                        'backend': 'myapp.MySpecialBackend',
                        'groups': ['cron'],
                },
                'special': {
                        'backend': 'myapp.MySpecialBackend',
                        'groups': ['cron'],
                },
                'another': {
                        'backend': 'myapp.AnotherBackend',
                },
    },
}

Now you'll be able to use the --group option of the runtasks management command to selectively run tasks: .. code-block:: python

python manage.py runtasks --group cron

Your crontab would now look like this: .. code-block:: python

*/5 * * * * python /path/to/manage.py runtasks --group cron

TIP

If you plan to use a cron job to trigger task execution, it's a good idea to always create a "cron" group. That way, if you ever add new non-cron backends, you won't have to change your crontab; you just won't add your new backend to the "cron" group.

Logging

Periodically uses Django's logging system to let you know when something goes wrong. To enable this, just add a "periodically" logger to your settings.py file:

LOGGING = {
        ...
    # This part should be in your settings file by default.
    'handlers': {
        'mail_admins': {
            'level': 'ERROR',
            'class': 'django.utils.log.AdminEmailHandler'
        }
    },
    'loggers': {
        ...
        # Add the following to enable logging for Periodically.
        'periodically': {
            'handlers': ['mail_admins'],
            'level': 'ERROR',
            'propagate': True,
        },
    },
}

This is a relatively simple setup that will send an email to the site admins whenever a periodic task fails, but Django is capable of much more. For more information, check out [the Django docs](https://docs.djangoproject.com/en/dev/topics/logging/).