Case statement for setting var in Ansible/Jinja2 -

i'm using ansible jinja2 templates, , scenario can't find solution in ansible's documentation or googling around jinja2 examples. here's logic want achieve in ansible:

if {{ existing_ansible_var }} == "string1"   new_ansible_var = "a" else if {{ existing_ansible_var }} == "string2"   new_ansible_var = "b" <...> else   new_ansible_var = "" 

i combining several techniques, variable assignment here: set variable in jinja, conditional comparison here: http://jinja.pocoo.org/docs/dev/templates/#if-expression, , defaulting filter here: https://docs.ansible.com/playbooks_filters.html#defaulting-undefined-variables ,

...but feel that's overkill. there simpler way this?

if want output value in template depending on value of existing_ansible_var use dict , feed existing_ansible_var.

{{ {"string1": "a", "string2": "b"}[existing_ansible_var] | default("") }} 

you can define new variable same way:

{% set new_ansible_var = {"string1": "a", "string2": "b"}[existing_ansible_var] | default("") -%} 

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in case existing_ansible_var might not defined, need catch default() not exist in dict:

{"string1": "a", "string2": "b"}[existing_ansible_var | default("this key not exist in dict")] | default("") 

---

you can define in playbook , later use new_ansible_var in template:

vars:     mydict: {"string1": "a", "string2": "b"}    new_ansible_var: '{{mydict[existing_ansible_var | default("this key not exist in dict")] | default("") }}'