Ansible : strange jinja2 behaviour with lowercase

can anyone explain the following Jinja behaviour in Ansible?

The following code works: The task is skipped because the job_function is not in the exclusion_functions array

- name: Lowercase test
  hosts: localhost
  gather_facts: false
  vars:
    job_function: 'VRIJwillig'
    exclusion_functions:
      - vrijwilliger
      - maatje

  tasks:
    - name: Test for function in exclusions
      debug:
        msg: In exclusions
      when: (job_function | lower) in exclusion_functions

The following code works as well, the second task is skipped.

- name: Lowercase test
  hosts: localhost
  gather_facts: false
  vars:
    job_function: 'VRIJwillig'
    exclusion_functions:
      - Vrijwilliger
      - Maatje

  tasks:
    - name: Initialiseer variabelen
      set_fact:
        exclusions: "{{ exclusion_functions | lower }}"

    - name: Test for function in exclusions
      debug:
        msg: In exclusions
      when: (job_function | lower) in exclusions

But this doesn't work, the task isn't skipped:

---
- name: Lowercase test
  hosts: localhost
  gather_facts: false
  vars:
    job_function: 'VRIJwillig'
    exclusion_functions:
      - Vrijwilliger
      - Maatje

  tasks:
    - name: Test for function in exclusions
      debug:
        msg: In exclusions
      when: (job_function | lower) in (exclusion_functions | lower)

Why is the task not skipped in the last code snippet? job_function | lower is vrijwillig, and exclusion_functions | lower is ['vrijwilliger','maatje'], and the first one isn't in the second one.

Solution

The value of the variable exclusion_functions is a list

    - debug:
        msg: |
          {{ exclusion_functions }}
          {{ exclusion_functions | type_debug }}

gives

  msg: |-
    ['Vrijwilliger', 'Maatje']
    list

The filter lower converts the argument to a string

    - debug:
        msg: |
          {{ exclusion_functions | lower }}
          {{ exclusion_functions | lower | type_debug }}

The output looks like a list but it isn't. It's a string

  msg: |-
    ['vrijwilliger', 'maatje']
    str

This explains why the below task isn't skipped

    - name: Test for function in exclusions
      debug:
        msg: In exclusions
      when: (job_function | lower) in (exclusion_functions | lower)

The value VRIJwillig of the variable job_function is converted to lowercase vrijwillig which is in the string ['vrijwilliger', 'maatje']

The solution is to map the filter lower to each list's item

    - debug:
        msg: |
          {{ exclusion_functions | map('lower') }}
          {{ exclusion_functions | map('lower') | type_debug }}

shows the result is a list with items converted to lowercase

  msg: |-
    ['vrijwilliger', 'maatje']
    list

Then, as expected, the below task is skipped

    - name: Test for function in exclusions
      debug:
        msg: In exclusions
      when: (job_function | lower) in (exclusion_functions | map('lower'))

^{Example of a complete playbook for testing
- name: Lowercase test
hosts: localhost

vars:

job_function: VRIJwillig
exclusion_functions:
- Vrijwilliger
- Maatje

tasks:

- debug:
msg: |
{{ exclusion_functions }}
{{ exclusion_functions | type_debug }}

- debug:
msg: |
{{ exclusion_functions | lower }}
{{ exclusion_functions | lower | type_debug }}

- name: Test for function in exclusions
debug:
msg: In exclusions
when: (job_function | lower) in (exclusion_functions | lower)

- debug:
msg: |
{{ exclusion_functions | map('lower') }}
{{ exclusion_functions | map('lower') | type_debug }}

- name: Test for function in exclusions
debug:
msg: In exclusions
when: (job_function | lower) in (exclusion_functions | map('lower'))}