Merge two dictionaries in Jinja2

Question

I have some code which basically searches some YAML files for Jinja2 variables and replaces them where appropriate. I want to be able to combine to YAML dicts together and was looking for a way to do this using the default Jinja2 library.

Here is some example YAML of what I am trying to a achieve:

---

vars.yml

vars:
  default:
    name: test1
    location: UK
  new:
    name: test2
    country: UK

---

template.yml

test: {{ vars.default.update(vars.new) }}

---

This would ideally output something like:

output.yml

test:
  name: test2
  location : UK
  country: UK

I am looking for a way to merge two dictionaries together using this method. The Jinja2 documentation don't appear to have an inbuilt function like the Ansible combine filter.

Is it possible that I just import this feature into my code or create a similar feature? I noticed that it is not included in the standard library for Ansible Jinja2 filters

When trying to use the update filter (which doesn't appear to exist in the Jinja2 documentation) I get a None result.

Answer 1

The update method of a dictionary is actually updating the source dictionary, not returning the merged dictionaries.

update([other])
Update the dictionary with the key/value pairs from other, overwriting existing keys. Return None.

^{Source: https://docs.python.org/3/library/stdtypes.html#dict.update}

So, you have two ways of achieving it:

• either you have the expression-statement extension loaded and you can use the {% do ... %} construct:

  {% do vars.default.update(vars.new) -%}
  test: {{ vars.default }}
  

• or it is not activated and you can use a dummy assignation:

  {% set noop = vars.default.update(vars.new) -%}
  test: {{ vars.default }}