Jinja "eval" type method?

[Brian Little]

Is there anything in jinja templating to "eval" a variable name? Where I can add a string to a variable, and reference another variable
I'm interesting in doing something like this (example pseudocode)

#print the mac addresses and driver (or similar)
{% for interface in ansible_interfaces %}

{{ interface }}
mac= {{ eval('ansible_' + interface).macaddress }}
driver = {{ eval('ansible_' + interface).module }}

{% endfor %}


Where the host variables are like this ( an example ):

"ansible_interfaces": [
  "eth1",
  "eth2"
],
"ansible_eth1": {
  "active": false",
  "device": "eth1",
  "macaddress": "00:00:00:FF:FF:FF",
  "module": "igb",
  "mtu": 1500,
  "type": "ether"
},
"ansible_eth2": {
  "active": false",
  "device": "eth2",
  "macaddress": "AA:00:00:FF:FF:AA",
  "module": "ixgbe",
  "mtu": 9000,
  "type": "ether"
},

Is something like this possible, or do I have to some combination of templating using with_items, and then using assemble to stick it together?

[Michael DeHaan]

Thank God, no Python evals.

You can access hostvars programatically like this:

hostvars[hostname][factname]

So you can build the factname string programatically and get to them that way.

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Michael DeHaan <mic...@ansibleworks.com>
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[Jan-Piet Mens]

> Is there anything in jinja templating to "eval" a variable name? Where I
> can add a string to a variable, and reference another variable
> I'm interesting in doing something like this (example pseudocode)

I did this recently for testing a lookup plugin; I think it's along the
lines of what you want:

{% for name in names -%}

{# Build param consisting of key and file= #}
{%
set param = ' '.join(( name, "file=input.csv", "default=OhNo!", "delimiter=;"))
-%}
{% set val = lookup('csvfile', param) -%}
{{ name }} is in fact "{{ val }}"
{% endfor %}

using the variables you want, of course. :)

-JP

[Michael DeHaan]

Random aside:  using that CSV lookup plugin will be pretty inefficient -- particularly in larger setups.  It will load the local file for every host in the host loop, and then once for every name in the names list.

A better way to do this would be to save the mapping as a YAML dictionary and use the stock systems in Ansible here.   However, that's not always possible.

The idea of a way to cache lookup plugin results was explored previously though technically requires some IPC so we maintain the cache in one process *OR* we extend fact caching proposed for 1.5 to also cache lookup plugin results when evaluated, with, say, lookup_cached, versus lookup, and specify a timeout.

lookup_cached('plugin_name', 'param string', timeout_in_seconds)

Hmmm.... ideas.... :)

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[Massimiliano Adamo]

Il giorno mercoledì 27 novembre 2013 17:53:29 UTC+1, Michael DeHaan ha scritto:

Thank God, no Python evals.

Thanks God ERB templates allow to embed Ruby code. 

It is discouraged, but when it's really necessary you can do it!. 

 

-- 

Massimiliano Adamo