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Mistral IndexError in line 290

asked 2016-01-21 19:28:14 -0500

michael@plexxi gravatar image

I'm running mistral version 0.1.2 on a workflow that does both fork/join and with-item multiple executions. Mistral is failing with the following: File "/opt/mistral/virtualenv/lib/python2.7/site-packages/mistral/workflow/", line 290, in _triggers_join in_t_ex = in_t_execs[-1] IndexError: list index out of range

Looking at that code I'm seeing the following comments:

# TODO(rakhmerov): Method signature is incorrect given that
# we may have multiple task executions for a task. It should
# accept inbound task execution rather than a spec.
def _triggers_join(self, join_task_spec, inbound_task_spec):


# TODO(rakhmerov): Temporary hack. See the previous comment.
      in_t_ex = in_t_execs[-1]

Is there a known bug or deficiency here?

Thanks! - Michael

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answered 2016-07-17 07:35:18 -0500

michal-gershenzon gravatar image

Adding this answer in case someones reads this in the future.

This issue is solved on master(Newton) : (

It is also possible to fix it with one line in Liberty: On the Mistral VM in file: /usr/lib/python2.7/site-packages/mistral/workflow/

Change Line 284 from:

       in_t_ex = in_t_execs[-1]

To this:

       in_t_ex = in_t_execs[-1] if in_t_execs else None
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Asked: 2016-01-20 19:41:06 -0500

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Last updated: Jul 17 '16