# How to solve ansible challenge from ansible-core maintainer

**URL:** <https://forum.ansible.com/t/how-to-solve-ansible-challenge-from-ansible-core-maintainer/45285>\
**Category:** Guides, FAQs & Howtos\
**Tags:** cfgmgmgtcamp, ansible-core, howto\
**Created:** [February 6, 2026, 3:24pm UTC](https://forum.ansible.com/t/how-to-solve-ansible-challenge-from-ansible-core-maintainer/45285 "2026-02-06T15:24:04Z")\
**Posts on this page:** 1\
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**Author:** ![nitzmahone](https://avatars.discourse-cdn.com/v4/letter/n/c5a1d2/32.png) [@nitzmahone](https://forum.ansible.com/u/nitzmahone)\
**Post date:** [February 14, 2026, 1:01am UTC](https://forum.ansible.com/t/how-to-solve-ansible-challenge-from-ansible-core-maintainer/45285/2 "2026-02-14T01:01:02Z")

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Heh, yep, we trod a lot of the same ground screwing around with this 😃.

This one in particular is very difficult because the interface detail mappings are not in a dedicated container- they’re intermixed with the rest of the facts. My initial attempts used the top-level `ansible_` prefixed values (not the un-prefixed ones under `ansible_facts`), which made it even harder because you have to make an intermediate projection of the names from `ansible_interfaces` to add the prefixes before you can dereference only those keys). Jinja’s rudimentary built-in `select/reject` (et al) require custom Jinja Test plugins to do arbitrary filtration- you can’t just give it an expression as you would with a comprehension, so you end up having to make numerous passes over the data- either with stored intermediate stages (verbose) or a giant chain of Jinja (verbose, inscrutable, and not-great-performance if done outside `set_fact`).

Last year, I hacked up some modifications to select/reject/et al that accepted Jinja macros in addition to test names- infinitely more powerful, but still doesn’t “read” nicely since you can’t just inline the expression as you would with a lambda or comprehension, and to do “near inline” macros requires a full template, not just a naked expression.

This time, I hacked up net-new comprehension filters that just accept expressions as strings that get compiled and invoked through a Python comprehension- they read _almost_ identically to Python dict/list comprehensions, though quoting is still obnoxious. That’s the thing I’d like to move forward with. The current UX is still pretty crappy IMO, and I didn’t have enough time to do the concept justice in my talk, so I didn’t show them to anyone, but it did work surprisingly well.

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