WTF bool filter in Ansible

It’s not what you think

Jinja2 filters:

• foo|list converts foo to list
• foo|string converts foo to string
• foo|int converts foo to int
• foo|float converts foo to float
• foo|bool IS NOT !!!!!!!!!11111one

Instead it parses foo as string to search for yaml-style ‘yes, on, true, false, False, Off, NO’ and other words and return true if any ‘yes’ word found.

"yes"|bool -> true
"no"|bool -> false
"funking yes"|bool -> false
"http://url"|bool -> false
[1,2,3]|bool -> false

In other words it’s not a usual map to python type constructor, but a separate ‘|guess_yes’ filter, named bool to cast confusions and wtfs.

Solution

Use round brackets to force the usual pythonic ‘falsable’ behavior:

when: (foo)

It will cast foo to False for:

• null
• None
• False
• Empty string
• empty list, dict, set

It will cast to True for:

• non-empty string, dict, list, set.
• True value

The Solution (updated)

drew1kun pointed out, that there is a (new?) filter in Ansible for this purpose:

foo is truthy

It handles values as Python does, e.g.:

• [] -> False
• {} -> False
• ‘no’ -> True
• ‘yes’ -> True
• [1] -> True
• “a” -> True
• “” -> False
• etc.