# Scheduling Tasks

On Posix systems, using cron is a perfectly valid way to schedule tasks for your application.

However, it sometimes happen that you need to interact intimately with the runtime environment of your application, that you need to schedule jobs dynamically, or that your hosting service does not provide access to cron. In those cases, you can schedule jobs with the TGScheduler module.

## Installation

TGScheduler is registered on PyPI and therefore can be installed with pip install:

    $ pip install tgscheduler

## Setup

TGScheduler is not started by default. To allow your tasks to run, simply start the scheduler when your application is loaded configured.

You can do that in `config/app_cfg.py`:

    def start_tgscheduler():
        import tgscheduler
        tgscheduler.start_scheduler()

    from tg.configuration import milestones
    milestones.config_ready.register(start_tgscheduler)

Using a Configuration Milestones ensures that our scheduler is not started twice, it is also suggested to register tasks inside the `start_tgscheduler` function so that they are not scheduled twice.

## Scheduling Tasks

To you have four ways to schudule tasks:

- add_interval_task();
- add_monthly_task();
- add_single_task();
- add_weekday_task().

Each of those receive a callable and a time specifier that defines when to run a function. As an example, if you want to update the stock prices in your database every 15 minutes, you would do something like the following:

    def update_stocks():
        url = 'http://example.com/stock_prices.xml'
        data = urllib2.urlopen(url).read()
        etree = lxml.etree.fromtsring(data)
        for el in etree.xpath("//stock"):
            price = model.StockPrice(el.get("name"), int(el.get("price")))
            model.DBSession.add(price)

    def start_tgscheduler():
        import tgscheduler
        tgscheduler.start_scheduler()
        tgscheduler.add_interval_task(60*15, update_stocks)

    from tg.configuration import milestones
    milestones.config_ready.register(start_tgscheduler)

Note

Inside the scheduled tasks you won’t have TurboGears automatically flushing and committing transactions for you, so remember to add a `transaction.commit()` call a the end of your tasks if your application is relying on the transaction manager.