Return updated unsorted dict in Ansible

I am trying to merge some dicts with saving their items on their own places like it is working in python using dict.update(), but i have some troubles with it in Ansible.

For example, I have two dicts:

dict1:
  c_value: None

dict2:
  b_value: None
  a_value: None

I want to merge them with saving order:

dict3:
  c_value: None
  b_value: None
  a_value: None

I have tried 2 solutions, using jinja2 and ansible filter combine. All of them works fine in jinja2 online editors, but if i use it in ansible - debugging shows that I have sorted dict by key name:

dict3:
  a_value: None
  b_value: None
  c_value: None

Jinja2 template: {%-set _ = dict1.update(dict2) -%}{{- dict1 -}}

Ansible combine: dict1 | combine(dict2)

A dictionary aka mapping is:

> "an unordered set of key/value node pairs, ..."

In other words, in YAML, there is no order in the dictionary's keys. What you see is probably Python 3.7+:

> "A dictionary now displays in the lexical order that variables were defined. Previously, the order was undefined."

See what Python your version of Ansible uses (on the controller)

shell> ansible --version
ansible [core 2.14.3]
  ...
  python version = 3.9.17 (main, Jun  6 2023, 20:11:04) [GCC 9.4.0] (/usr/bin/python3.9)
  jinja version = 3.1.2
  libyaml = True

Given the dictionaries

  dict1:
    c_value: None
  dict2:
    b_value: None
    a_value: None

combine them

  dict3: "{{ dict1|combine(dict2) }}"

• The keys are ordered lexicographically by Python 3.7+

    - debug:
        msg: |
                    {{ dict3 }}

gives

  msg:
    a_value: None
    b_value: None
    c_value: None

• You have to declare another order of keys if you want to. For example,

    - debug:
        msg: |
          {% for k in key_order %}
          {{ k }}: {{ dict3[k] }}
          {% endfor %}          
      vars:
        key_order: [c_value, b_value, a_value]

gives

  msg: |-
    c_value: None
    b_value: None
    a_value: None    

• But, if you convert the text to YAML you get the ordered keys again

    - debug:
        msg: |
          {% filter from_yaml %}
          {% for k in key_order %}
          {{ k }}: {{ dict3[k] }}
          {% endfor %}
          {% endfilter %}          
      vars:
        key_order: [c_value, b_value, a_value]

gives

  msg:
    a_value: None
    b_value: None
    c_value: None

<hr>

<sup>

Example of a complete playbook for testing

- hosts: localhost

  vars:

    dict1:
      c_value: None
    dict2:
      b_value: None
      a_value: None

    dict3: "{{ dict1|combine(dict2) }}"

  tasks:

    - debug:
        msg: |
                    {{ dict3 }}

    - debug:
        msg: |
          {% for k in key_order %}
          {{ k }}: {{ dict3[k] }}
          {% endfor %}          
      vars:
        key_order: [c_value, b_value, a_value]

    - debug:
        msg: |
          {% filter from_yaml %}
          {% for k in key_order %}
          {{ k }}: {{ dict3[k] }}
          {% endfor %}
          {% endfilter %}          
      vars:
        key_order: [c_value, b_value, a_value]

</sup>