# Undefined variables and filter subelements **URL:** \ **Category:** Ansible Project\ **Created:** [November 7, 2019, 12:43pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616 "2019-11-07T12:43:02Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Tobias\_Kirchhofer](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tobias\_Kirchhofer](https://forum.ansible.com/u/Tobias_Kirchhofer)\ **Post date:** [November 7, 2019, 12:43pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/1 "2019-11-07T12:43:02Z")
We think we experience an anomalie with undefined variables and usage of subelements: ` - name: Enable/disable service firewalld: zone: “{{ item.0.ZONE }}” service: “{{ item.1.SERVICE }}” permanent: yes immediate: yes state: “{{ item.1.STATE }}” loop: “{{ FIREWALLD\_ZONE\_SERVICE|subelements(‘SERVICES’) }}” when: FIREWALLD\_ZONE\_SERVICE is defined ` FIREWALLD\_ZONE\_SERVICE is NOT defined. Our expectation is that ansible will skip this task like it does at other tasks without sublements. With subelements in the loop ansible tries to resolve undefined FIREWALLD\_ZONE\_SERVICE and fails with an error: ` fatal: […]: FAILED! =\> {“msg”: “obj must be a list of dicts or a nested dict”} ` If FIREWALLD\_ZONE\_SERVICE is defined everything works like expected. Anyone? ---
**Author:** ![Tobias\_Kirchhofer](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tobias\_Kirchhofer](https://forum.ansible.com/u/Tobias_Kirchhofer)\ **Post date:** [November 8, 2019, 11:54am UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/2 "2019-11-08T11:54:47Z")
Maybe i was not precise enough. Situation is this: If the var is defined it looks like this: ` FIREWALLD\_ZONE\_SERVICE: - ZONE: public SERVICES: - SERVICE: http STATE: enabled - SERVICE: https STATE: enabled ` We loop through SERVICES with ` FIREWALLD\_ZONE\_SERVICE|subelements(‘SERVICES’) ` This is fine as long the var is defined. It not we expect that ` when: FIREWALLD\_ZONE\_SERVICE is defined ` prevents the evaluation of the war in the loop. In another context it works fine: `loop: "{{ FIREWALLD_ZONE|product(FIREWALLD_ZONE.ZONES)|list }}"` ` when: FIREWALLD\_ZONE is defined ` If FIREWALLD\_ZONE is not defined the var in the loop is not evaluated. So the difference is: If we have ‘subelements’ in the loop ‘when: var is defined’ is not working. If we have eq. ‘product’ in the loop ‘when: var is defined’ works. More clear now? 🙂 Could someone spend some thoughts? Maybe it is a misunderstanding on our site… ---
**Author:** ![vbotka](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/vbotka/32/359_2.png) [@vbotka](https://forum.ansible.com/u/vbotka)\ **Post date:** [November 8, 2019, 12:31pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/3 "2019-11-08T12:31:46Z")
Use \*default\* and \*skip\_missing\* subelements. For example     loop: "{{ FIREWALLD\_ZONE\_SERVICE|default()|               subelements('SERVICES', skip\_missing=True) }}" Cheers,   -vlado ---
**Author:** ![Tobias\_Kirchhofer](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tobias\_Kirchhofer](https://forum.ansible.com/u/Tobias_Kirchhofer)\ **Post date:** [November 8, 2019, 2:13pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/4 "2019-11-08T14:13:10Z")
> Use _default_ and _skip\_missing_ subelements. For example > > loop: “{{ FIREWALLD\_ZONE\_SERVICE|default()| > subelements(‘SERVICES’, skip\_missing=True) }}” Thank you! This is working. Is only needed with ‘subelements’. But why? Anyway - thanks! 🙂 ---
**Author:** ![vbotka](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/vbotka/32/359_2.png) [@vbotka](https://forum.ansible.com/u/vbotka)\ **Post date:** [November 8, 2019, 3:55pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/5 "2019-11-08T15:55:59Z")
I guess   - \*subelements\* filter is executed before \*when\*, because   - \*when\* is evaluated on each iteration, because   - \*when\* argument can change on each iteration (e.g. may include \*item\*).   - \*when\* can not be evaluated before \*subelements\*, because \*item\* does not     exist yet. The loop will fail     loop: "{{ FIREWALLD\_ZONE\_SERVICE|subelements('SERVICES') }}"   when: FIREWALLD\_ZONE\_SERVICE is defined   FAILED! =\> {"msg": "'FIREWALLD\_ZONE\_SERVICE' is undefined"} The loop below is skipped when FIREWALLD\_ZONE\_SERVICE is not defined (this is not consistent, it should also fail. Source would reveal why)     loop: "{{ FIREWALLD\_ZONE\_SERVICE }}"   when: FIREWALLD\_ZONE\_SERVICE is defined ,but it will also fail if the evaluation of the \*loop\* argument (FIREWALLD\_ZONE\_SERVICE) before \*when\* is forced e.g.     loop: "{{ FIREWALLD\_ZONE\_SERVICE }}"   when: item|length \> 10 and         FIREWALLD\_ZONE\_SERVICE is defined            FAILED! =\> {"msg": "'FIREWALLD\_ZONE\_SERVICE' is undefined"} Cheers,   -vlado ---
**Author:** ![vbotka](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/vbotka/32/359_2.png) [@vbotka](https://forum.ansible.com/u/vbotka)\ **Post date:** [November 8, 2019, 4:07pm UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/6 "2019-11-08T16:07:01Z")
As a result, \*default\* is better construct        loop: "{{ FIREWALLD\_ZONE\_SERVICE|default() }}" than \*when\*        loop: "{{ FIREWALLD\_ZONE\_SERVICE }}"      when: FIREWALLD\_ZONE\_SERVICE is defined ---
**Author:** ![Tobias\_Kirchhofer](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tobias\_Kirchhofer](https://forum.ansible.com/u/Tobias_Kirchhofer)\ **Post date:** [November 9, 2019, 8:04am UTC](https://forum.ansible.com/t/undefined-variables-and-filter-subelements/31616/7 "2019-11-09T08:04:09Z")
Thank you for the [b](https://groups.google.com/forum/#!msg/ansible-project/Y1mGC3vrsng/8DZRiJU6AwAJ)ackground explanation! Interesting.