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Utilities

Scheduling Tasks

On Posix systems, using cron is a perfectly valid way to schedule tasks for your application. See Command Line Scripts for an example of script that can access all of the application model and internals and that is therefore an ideal target for a cron job.

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 easy_install:

$ easy_install tgschuduler

Setup

TGScheduler is not started by default. To allow your tasks to run, simply start the scheduler when your application is loaded. You can do that in lib/app_globals.py:

import tgscheduler

class Globals(object):
    def __init__(self):
        tgscheduler.start_scheduler()

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)

class Globals(object):
    def __init__(self):
        tgscheduler.start_scheduler()
        tgscheduler.add_interval_task(60*15, update_stocks)