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Django ZTask - A simple background task scheduler for Django

Project Description

In version 0.1.4, we are introducing two major changes:

1. Tasks now have a "created" datetime field. This was added to make sure `--replayfailed` replayed tasks in the appropriate order
2. Introduced [South]( migrations.

IF YOU HAVE ALREADY INSTALLED django-ztask - you can "fake" the first migration, and then run the second migration:

./ migrate django_ztask --fake 0001
./ migrate django_ztask

If you are not using [South]( in your Django project, it is strongly recommended you do. If you
are not, you will have to add the "created" field to your database manually.


Download and install 0MQ version 2.1.3 or better from [](

Install pyzmq and django_ztaskd using PIP:

pip install pyzmq
pip install -e

Add `django_ztask` to your `INSTALLED_APPS` setting in ``


Then run `syncdb`

python syncdb

Running the server

Run django-ztask using the command:

python ztaskd

Command-line arguments

The `ztaskd` command takes a series of command-line arguments:

- `--noreload`

By default, `ztaskd` will use the built-in Django reloader
to reload the server whenever a change is made to a python file. Passing
in `--noreload` will prevent it from listening for changed files.
(Good to use in production.)

- `-l` or `--loglevel`

Choose from the standard `CRITICAL`, `ERROR`, `WARNING`,
`INFO`, `DEBUG`, or `NOTSET`. If this argument isn't passed
in, `INFO` is used by default.

- `-f` or `--logfile`

The file to log messages to. By default, all messages are logged
to `stdout`

- `--replayfailed`

If a command has failed more times than allowed in the
`ZTASKD_RETRY_COUNT` (see below for more), the task is
logged as failed. Passing in `--replayfailed` will cause all
failed tasks to be re-run.


There are several settings that you can put in your `` file in
your Django project. These are the settings and their defaults

ZTASKD_URL = 'tcp://'

By default, `ztaskd` will run over TCP, listening on port 5555.


If set to `True`, all `.async` and `.after` tasks will be run in-process and
not sent to the `ztaskd` process. Good for task debugging.


If set, all tasks will be logged, but not executed. This setting is often
used during testing runs. If you set `ZTASKD_DISABLED` before running
`python test`, tasks will be logged, but not executed.


The number of times a task should be reattempted before it is considered failed.


The number, in seconds, to wait in-between task retries.


This is a list of callables - either classes or functions - that are called when the server first
starts. This is implemented to support several possible Django setup scenarios when launching
`ztask` - for an example, see the section below called **Implementing with Johnny Cache**.

Running in production

A recommended way to run in production would be to put something similar to
the following in to your `rc.local` file. This example has been tested on
Ubuntu 10.04 and Ubuntu 10.10:

#!/bin/bash -e
pushd /var/www/path/to/site
sudo -u www-data python ztaskd --noreload -f /var/log/ztaskd.log &

Making functions in to tasks

Decorators and function extensions make tasks able to run.
Unlike some solutions, tasks can be in any file anywhere.
When the file is imported, `ztaskd` will register the task for running.

**Important note: all functions and their arguments must be able to be pickled.**

([Read more about pickling here](

It is a recommended best practice that instead of passing a Django model object
to a task, you intead pass along the model's ID or primary key, and re-get
the object in the task function.

The @task Decorator

from django_ztask.decorators import task

The `@task()` decorator will turn any normal function in to a
`django_ztask` task if called using one of the function extensions.

Function extensions

Any function can be called in one of three ways:

- `func(*args, *kwargs)`

Calling a function normally will bypass the decorator and call the function directly

- `func.async(*args, **kwargs)`

Calling a function with `.async` will cause the function task to be called asyncronously
on the ztaskd server. For backwards compatability, `.delay` will do the same thing as `.async`, but is deprecated.

- `func.after(seconds, *args, **kwargs)`

This will cause the task to be sent to the `ztaskd` server, which will wait `seconds`
seconds to execute.


from django_ztask.decorators import task

def print_this(what_to_print):
print what_to_print

if __name__ == '__main__':

# Call the function directly
print_this('Hello world!')

# Call the function asynchronously
print_this.async('This will print to the ztaskd log')

# Call the function asynchronously
# after a 5 second delay
print_this.after(5, 'This will print to the ztaskd log')

Implementing with Johnny Cache

Because [Johnny Cache]( monkey-patches all the Django query compilers,
any changes to models in django-ztask that aren't properly patched won't reflect on your site until the cache
is cleared. Since django-ztask doesn't concern itself with Middleware, you must put Johnny Cache's query cache
middleware in as a callable in the `ZTASKD_ON_LOAD` setting.


If you wanted to do this and other things, you could write your own function, and pass that in to
`ZTASKD_ON_LOAD`, as in this example:


def ztaskd_startup_stuff():
Stuff to run every time the ztaskd server
is started or reloaded
from johnny import middleware
... # Other setup stuff



See: [](
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