Workflow V2.1.6 - KeyError: 'previous_data'

[GaryRevell]

Trying out the sample code from the documentation "Loops and interrupts" from this page
https://workflow.readthedocs.io/en/latest/#contributing

And get the following stack dump:

grevell@grevell-mac workflow % py3 wf_complex.py
new data: [0]
new data: [0, 1]
Traceback (most recent call last):
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 540, in _process
exception_handler = getattr(
AttributeError: type object 'TransitionActions' has no attribute 'KeyError'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/Users/grevell/Documents/dev/python/workflow/wf_complex.py", line 77, in
my_engine.process([[], [0,1], [0,1,0,1]])
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 390, in process
self._process(objects)
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 546, in _process
self.processing_factory.transition_exception_mapper.Exception( # noqa
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 970, in Exception
reraise(*exc_info)
File "/opt/homebrew/lib/python3.9/site-packages/six.py", line 719, in reraise
raise value
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 529, in _process
self.run_callbacks(callbacks, objects, obj)
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 462, in run_callbacks
self.run_callbacks(inner_callbacks,
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 481, in run_callbacks
self.execute_callback(callback_func, obj)
File "/opt/homebrew/lib/python3.9/site-packages/workflow/engine.py", line 564, in execute_callback
callback(obj, self)
File "/opt/homebrew/lib/python3.9/site-packages/workflow/patterns/controlflow.py", line 338, in _for
eng.extra_data["_Iterators"][step]["previous_data"])
KeyError: 'previous_data'
grevell@grevell-mac workflow %

Not sure if this is still being worked on but it looks a very good candidate for what I need.

Thanks !

Gary