Processing a List in a Dictionary - list

Question

I am trying to process a dictionary of tags to produce a command line that will be passed to a python program that will apply tags to an object. Tags can be either single cardinality (i.e. the "key" can appear only once on the tagged element) or multi-cardinality (i.e. the "key" can appear multiple times on the element). Single Cardinality tagging is fine, my problem is with multi-cardinality.
The dictionary in the ansible host_vars file would be:
multi_tags:
multi_tag1: value1
multi_tag2: mvalue1
multi_tag2: mvalue2
multi_tag3: value3
But ansible will replace "multi_tag2" with "mvalue2" only because you can't have 2 variables with the same name. Therefore the dictionary actually looks like:
multi_tags:
multi_tag1: value1
multi_tag2: ["mvalue1", "mvalue2"]
multi_tag3: value3
At the end of this I need to produce the following list:
multi_tag1:value1, multi_tag2:mvalue1, multi_tag2:mvalue2, multi_tag3:value3
So far i've been able to get multi_tag1:value1, multi_tag2:[mvalue1, mvalue2], multi_tag3:value3, and I can detect that mutli_tag2 is a list, but I cannot figure out how to pull "multi_tag2", separate from the multi_tags dict and then expand that list into it's individual key:value components?
NOTE: "multi_tag2" may be any name and there may be any number of lists like this in the dictionary. The challenge is in reading the dictionary, finding all of the list keys and spinning each list key into its own expanded key:value set.
I can detect and capture list name keys with:
- name: Caputre Lists for Processing
vars:
multilist: []
set_fact:
multilist: "{{ multilist + [item] }}"
with_items: '{{ multi_tags.keys() }}'
when: ( multi_tags[item] is defined ) and ( multi_tags[item] | type_debug == "list" )
But once I have the "list of lists" I don't know how to then spin that to generate/expand each key:value pair in each list to create the final consolidated group of key:value pairs.
This does not need to be done in one step, i'm happy to add the expanded key:value pairs to additional set-facts and then combine the single facts with the "list" facts to create the final key:value list if that's needed.
I've been racking my brain over this for hours now. Any advice would be helpful!

Answer 1

Create a list of products first. The challenge is converting a string to a list where this string is a single item. Simply item|list won't work because a string is iterable. Hence, it must be closed in brackets [item]. This would create a nested list, if the item is already a list, which must be flattened, e.g.
- set_fact:
mtl: "{{ mtl|d([]) + [item.key]|product([item.value]|flatten) }}"
loop: "{{ multi_tags|dict2items }}"
gives
mtl:
- - multi_tag1
- value1
- - multi_tag2
- mvalue1
- - multi_tag2
- mvalue2
- - multi_tag3
- value3
Then, join the items, e.g.
- debug:
msg: "{{ mtl|map('join', ':')|join(', ') }}"
gives
msg: multi_tag1:value1, multi_tag2:mvalue1, multi_tag2:mvalue2, multi_tag3:value3