TaskFlow/Task Arguments and Results

Overview

In TaskFlow, all flow state should go to storage. That includes all the information that task needs when it is executed (task arguments), and all the information task produces (task results). Developer who implements task or flow can specify what arguments task accepts and what result it returns in several ways.

Set of names of task arguments is available as requires property of the task instance. When task is about to be executed values with this names are retrieved from storage and passed to execute method of the task as keyword arguments.

Set of names of task results (what task provides) is available as provides property of task instance. After task finishes successfully, it's result(s) (what task execute method returns) are available by these names from storage (there will be examples below).

Arguments Specification

There are different way to specify task argument set.

Arguments Inference

Task arguments can be inferred from arguments of execute method of the task. For example:

   >>> class MyTask(task.Task):
   ...     def execute(self, spam, eggs):
   ...         return spam + eggs
   ... 
   >>> MyTask().requires
   set(['eggs', 'spam'])

Inference from signature is simplest way to specify task arguments. Optional arguments (with default values), and special arguments like self, *args and **kwargs are ignored on iferrence:

   >>> class MyTask(task.Task):
   ...     def execute(self, spam, eggs=()):
   ...         return spam + eggs
   ... 
   >>> MyTask().requires
   set(['spam'])
   >>>
   >>> class UniTask(task.Task):
   ...     def execute(self,  *args, **kwargs):
   ...         pass
   ... 
   >>> UniTask().requires
   set([])