Spiff Workflow is a library implementing a framework for workflows. It is based on http://www.workflowpatterns.com and implemented in pure Python.
In addition, Spiff Workflow provides a parser and workflow emulation layer that can be used to create executable Spiff Workflow specifications from Business Process Model and Notation (BPMN) documents.
For documentation please refer to:
https://github.com/knipknap/SpiffWorkflow/wiki
Mailing List: http://groups.google.com/group/spiff-devel/
Workflow.data - implements Workflow Data SubWorkflow.in_assign, out_assign - implements Block Data Task.data - implements Task Data Error handler is executed in a subworkflow. It's block Data inherited from failed task, and not comes back to parent workflow