Package: appenginetaskutils
# appenginetaskutilsThis is the repo for the appengine task utils library. It generates the appenginetaskutils package## InstallUse the python package for this library. You can find the package online [here](https://pypi.python.org/pypi/appenginetaskutils).Change to your Python App Engine project's root folder and do the following:> pip install appenginetaskutils --target libOr add it to your requirements.txt. You'll also need to set up vendoring, see [app engine vendoring instructions here](https://cloud.google.com/appengine/docs/python/tools/using-libraries-python-27).## @taskThe most basic element of the taskutils library is task(). This decorator function is designed to be used as a replacement for [deferred](https://cloud.google.com/appengine/articles/deferred).### Configuring @taskWhen using deferred you have a builtin to configure in app.yaml to make it work. For taskutils.task, you need to add the following to your app.yaml and/or \<servicename\>.yaml file:handlers:- url: /_ah/task/.*script: taskutils.applogin: adminThis rule creates a generic handler for task to defer work to background push tasks.Add it at the top of the list (to make sure other rules don't override it).### Importing taskYou can import task into your modules like this:from taskutils import task### Using task as a decoratorYou can take any function and make it run in a separate task, like this:@taskdef myfunction():... do stuff ...Just call the function normally, eg:myfunction()You can use @task on any function, including nested functions, recursive functions, recursive nested functions, the sky is the limit. This is possible because of use of [yccloudpickle](https://medium.com/the-infinite-machine/python-function-serialisation-with-yccloudpickle-b2ff6b2ad5da#.zei3n0ibu) as the underlying serialisation library.Your function can also have arguments, including other functions:def myouterfunction(mapf):@taskdef myinnerfunction(objects):for object in objects:mapf(object)...get some list of lists of objects...for objects in objectslist:myinnerfunction(objects)def dosomethingwithobject(object):... do something with an object ...myouterfunction(dosomethingwithobject)The functions and arguments are being serialised and deserialised for you behind the scenes.When enqueuing a background task, the App Engine Task and TaskQueue libraries can take a set of parameters. You can pass these to the decorator:@task(queue="myqueue", countdown=5)def anotherfunction():... do stuff ...Details of the arguments allowed to Tasks are available [here](https://cloud.google.com/appengine/docs/python/refdocs/google.appengine.api.taskqueue), under **class google.appengine.api.taskqueue.Task(payload=None, \*\*kwargs)**. The task decorator supports a couple of extra ones, detailed below.### Using task as a factoryYou can also use task to decorate a function on the fly, like this:def somefunction(a, b):... does something ...somefunctionintask = task(somefunction, queue="myqueue")Then you can call the function returned by task when you are ready:somefunctionintask(1, 2)You could do both of these steps at once, too:task(somefunction, queue="myqueue")(1, 2)### transactionalPass transactional=True to have your [task launch transactionally](https://cloud.google.com/appengine/docs/python/datastore/transactions#transactional_task_enqueuing). eg:@task(transactional=True)def myserioustransactionaltask():...### includeheadersIf you'd like access to headers in your function (a dictionary of headers passed to your task, it's a web request after all), set includeheaders=True in your call to @task. You'll also need to accept the headers argument in your function.@task(includeheaders=True)def myfunctionwithheaders(amount, headers):... stuff ...myfunctionwithheaders(10)App Engine passes useful information to your task in headers, for example X-Appengine-TaskRetryCount.### other bitsWhen using deferred, all your calls are logged as /_ah/queue/deferred. But @task uses a url of the form /_ah/task/\<module\>/\<function\>, eg:/_ah/task/mymodule/somefunctionwhich makes debugging a lot easier.