A framework that is similar to this in python (that I am one of the authors of) [1] (and [2] for more in-depth docs/examples). It's used in openstack (which some people may have heard of) where appropriate (and where desirable...) to help in consistent, scalable execution using a flow like methodology to declaratively describe workflows (and execute them using various strategies/engines).

[1] https://github.com/openstack/taskflow

[2] http://docs.openstack.org/developer/taskflow/