[openstack-dev] [oslo][mistral] Mistral expressions package

HADDLETON, Robert W (Bob) bob.haddleton at nokia.com
Tue Oct 10 00:41:58 UTC 2017

On 10/9/2017 2:35 PM, Doug Hellmann wrote:
> Excerpts from Bob Haddleton's message of 2017-10-09 11:35:16 -0500:
>> Hello Oslo team:
>> The Mistral project has an expressions package [0] that is used to
>> evaluate inline expressions using a context.  It has a pluggable
>> architecture that presently supports Jinja and YAQL expression
>> evaluation.  It also allows custom functions[1] to provide Python
>> implementations of functionality that is then made available to the
>> expression evaluation engines.
>> This functionality was originally developed to support dynamic
>> processing within Mistral workflows, but is also very useful in other
>> applications that use templates which require runtime evaluation of
>> expressions.
>> I'd like to explore extracting this functionality from mistral to make
>> it more widely available with minimal dependencies.
>> The expressions dependencies are pretty limited:
>> Jinja2
>> oslo.utils
>> oslo.log
>> stevedore
>> yaql
>> and since 60% are already oslo-maintained packages, it seemed like a
>> logical place to start.
>> I'd appreciate feedback on the topic.  There is no real OpenStack
>> dependency in the functionality, so maybe a standalone package on pypi
>> makes sense.
>> Thanks for your help,
>> Bob Haddleton
>> [0] https://github.com/openstack/mistral/tree/master/mistral/expressions
>> [1]
>> https://github.com/openstack/mistral/blob/master/mistral/utils/expression_utils.py#L63
> Oslo is a good place for things like this that have no other obvious
> home, but if the Mistral team is already managing the code is there any
> reason they couldn't also manage the library after you pull it out of
> the service? It's much easier for any project team to manage a library
> now, and we have several other examples of that pattern already.
> Doug
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Hi Doug:

That's probably fine, we're just not sure what the process should be and 
where the library would land?  Do you have an example that we could use 
as a pattern?



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