waterf 2

Chaining tasks on Google Appengine's (GAE) taskqueue.

A convenience module on top of the deferred library that comes with the Google AppEngine (GAE).

Note that you have to enable the deferred library in your app.yaml

builtins:
- deferred: on

In a nutshell:

from waterf import queue, task

queue.inorder(
    task(check_condition),
    queue.parallel(
        task(remove, id=101),
        task(remove, id=102),
        task(remove, id=103)
    ),
    task(email, to='[e-mail]')
).run()

Should be pretty self-explanatory: it first runs the function check_condition, then it runs the function remove three times in parallel, after that it runs email.

To abort execution of a series you either raise queue.PermanentTaskFailure or as a convenience return queue.ABORT.

You use task() exactly the same as you used deferred.defer():

task(check, id=102, _countdown=20)
task(email, to='[e-mail]', _queue='mailer')

After constructing a task you either run() or enqueue() it; whereby:

task(foo, 'bar').enqueue()  <==> deferred.defer(foo, 'bar')
task(foo, 'bar').run()      <==> foo('bar')

Read the tests. Thank you.