Flowy Docs

Flowy is a workflow modeling and execution library. A workflow is a process composed of independent and interdependent tasks. The independent tasks can be concurrent and can run in parallel on many machines. Flowy uses single-threaded Python code to model workflows. It infers the concurrency by building the task dependency graph at run-time. A workflow engine, like Amazon’s SWF, handles the task scheduling and routing. The engine also stores task results and a history of the entire workflow execution. An open source alternative to Amazon SWF is also available as part of the Eucalyptus project.

Modeling workflows with Python code is easy and familiar. It also gives the user great flexibility without sacrificing the readability. A toy example workflow, with Flowy, looks like this:

def sum_activity(a, b):
    return a + b

def square_activity(n):
    return n ** 2

class ExampleWorkflow(object):
    def __init__(self, square, sum):
        self.square = square
        self.sum = sum

    def __call__(self, a, b):
        a_squared = self.square(a)
        b_squared = self.square(b)
        return self.sum(a_squared, b_squared)

w = flowy.LocalWorkflow(ExampleWorkflow)
w.conf_activity('square', square_activity)
w.conf_activity('sum', sum_activity)
print(w.run(2, 10))

Getting Started

Flowy is available on the Python Package Index site. To install it use pip:

pip install flowy

Next, you should read the Tutorial. It provides a narrative introduction of the most important features of Flowy. It also shows how to run a workflow on different engines.




  • using boto3 as an underlaying for communicating with AWS SWF


  • A large and backward-incompatible rewrite.
  • Added a local engine that can run workflows on a single machine using threads or processes. This is handy for local development and quick prototypes.
  • Added workflow execution tracing and visualisation, as dot graphs, for the local engine.
  • Proxy objects replaced task results. This allows a workflow to run as single threaded Python code, without Flowy. It also makes testing more convenient.
  • Moved the workflow configuration outside of the workflow code. This makes it easy to configure the same workflow to run on different engines.