how to append to a list in jinja2 for ansible - templates

Question

Below is the jinja2 template that i wrote to use in ansible.
{% set port = 1234 %}
{% set server_ip = [] %}
{% for ip in host_ip %}
{% do server_ip.append({{ ip }}:{{ port }}) %}
{% endfor %}
{% server_ip|join(', ') %}
Below is the my desired output:
devices = 192.168.56.14:1234,192.168.56.13:1234,192.168.56.10:1234
But when i am running the ansible playbook, it is throwing the error as below:
"AnsibleError: teme templating string: Encountered unknown tag 'do'. Jinja was looking for th: 'endfor' or 'else'
Any help would be appreciated..

Answer 1

Try below code:
{% set port = '1234' %}
{% set server_ip = [] %}
{% for ip in host_ip %}
{{ server_ip.append( ip+":"+port ) }}
{% endfor %}
{{ server_ip|join(',') }}
You ll get:
192.168.56.14:1234,192.168.56.13:1234,192.168.56.10:1234

Answer 2

I didn't like any of the answers, they feel too hacky (having to worry about outputting None, or spurious whitespace using other techniques), but I think I've found a solution that works well. I took inspiration from this answer on a related question and realized that you can call set multiple times for the same variable and seemingly not incur any penalty.
It's still a tad hacky, because I don't think it's intended to work like this (then again, several design decisions in Jinja make me scratch my head, so who knows).
{% set server_ip = server_ip.append({{ ip }}:{{ port }}) %}
Interestingly, while the value is indeed appended to server_ip, the return value of that append (which we now know very well is None) isn't assigned back to server_ip on the LHS. Which led me to discover that the LHS side of the statement seems to be a no-op.
So you can also do this and the append works:
{% set tmp = server_ip.append({{ ip }}:{{ port }}) %}
Yet, if you print tmp, nothing shows up. Go figure.

Answer 3

That worked for me:
- set_fact:
devices: >-
{% for ip in host_ip %}{{ ip }}:1234{% if not loop.last %},{% endif %}{% endfor %}
If you still want to use do then add
jinja2_extensions = jinja2.ext.do
to your ansible config file and change
{% do server_ip.append({{ ip }}:{{ port }}) %}` to `{% do server_ip.append({ip:port}) %}`

Answer 4

The most voted answer will cause a lot of whitespaces in the rendered result. Beside using do extension from jinja, the alternative solution is using whitespace control from jinja. Add minus sign - inside the block
{%- for ip in host_ip -%}...{%- endfor %}
will remove the whitespace.

Answer 5

In order to avoid having None printed all over using {{ server_ip.append( ip+":"+port ) }} (just spent 20 min debugging this) and if you don't want to use the misleading {% set _ = server_ip.append( ip+":"+port ) %}, you can go back to Python basics and do the following:
# Remember that [1, 2] + [3] = [1, 2, 3]
{% set server_ip = server_ip + [ip+":"+port] %}
In 99.9% situations this will do the job. However in special cases where you work with very large lists there may be a small performance downside here in terms of memory usage: in the above example, [1, 2] + [3] = [1, 2, 3], both [1, 2] and [1, 2, 3] (initial and modified list) will coexist in memory for a brief moment, contrary to the append method which doesn't create additional objects in memory.

Answer 6

One-line solution with map() and regex:
{{ ["1.1.1.1","2.2.2.2"]|map('regex_replace', '(.+)', "\\1:1234")|join(', ') }}
map('regex_replace', '(.+)', "\\1:1234") adds :1234 to any non-empty string (.+) in the passed array ["1.1.1.1","2.2.2.2"]. Result:
1.1.1.1:1234, 2.2.2.2:1234