Open Stack

Hi Stan,

I had a quick(hopefully) question about MuranoPL that I hope you might 
be able to help with, Felipe had mentioned you are very knowledgeable in 
this area. If you don't have time please disregard!

I'm working on a patch for the Murano core library to make volume 
attachment info available, which is available at 
https://review.openstack.org/451909. It's mostly working, but I'm having 
some issues getting the types correct in MuranoPL to make this info 
consumable by end users.

The attachment info from a sample run in the stack $outputs looks like 
this (taken from the dashboard using $reporter)

u'vol-7c8ee61f-a444-46a1-ad70-fc6fce6a7b56-attachments': 
u"[{u'server_id': u'2891067b-e7bb-4ab9-a759-9e81096c0682', 
u'attachment_id': u'7456a4b0-3abd-48a0-a0cb-f3fa0f2706bb', 
u'attached_at': u'2017-03-30T16:51:57.000000', u'host_name': None, 
u'volume_id': u'373e4a5a-46b6-4091-82d6-b3dba62d552b', u'device': 
u'/dev/vda', u'id': u'373e4a5a-46b6-4091-82d6-b3dba62d552b'}]"

Here both key and value appear to be a string (note, I can't confirm 
this as the typeinfo function doesn't appear to be available in 
Instance.yaml for some reason... perhaps I'm using it wrong)

My goal is to then set this into a property of CinderVolume.yaml, with a 
Contract of '[]'. However, when I access this from a sample app, I end 
up with a list of strings, shown by $reporter as:

(u"[{u'server_id': u'2891067b-e7bb-4ab9-a759-9e81096c0682', 
u'attachment_id': u'f5bd50ab-4040-4e2b-8b50-790781d9bc37', 
u'attached_at': u'2017-03-30T16:51:59.000000', u'host_name': None, 
u'volume_id': u'ed7eb535-9e81-4c97-b063-86936d4ee306', u'device': 
u'/dev/vdb', u'id': u'ed7eb535-9e81-4c97-b063-86936d4ee306'}]",)

So my question is:

1) Why is the content of this 'get_attr' coming from heat being stored 
in the stack outputs as a string, and

2) Is there a way I can cast this to a list of dicts or similar 
structure so it can be iterated as expected?

Any tips much appreciated.

Thanks,
-Paul