How to pass actual python type (such as None) in yaml using a variable

[Andy]

Hi,

My problem is described here (MWE):

http://pastebin.com/27k4HHaU

Some modules allow you to pass yaml's null as a param which ends up as a python's None. For instance the mysql_user module here:

https://github.com/ansible/ansible/blob/devel/library/database/mysql_user#L164

won't change the password when null is passed:

- name: setup.mysql

  mysql_user:

    password: null

will only change privileges but not passwords (which the user may change). However if I pass a variable

- name: setup mysql

  mysql_user:

    password: "{{ pw }}"

I can't get it to work properly (as shown in the pastebin). This is with the latest devel.

Is there a way to get that behavior? Right now I have to create two lists (one which enforces passwords, one which does not).

Cheers

[Brian Coca]

password: !!null

there are other ways, but this is probably easiest to remember.

[Andy]

I'm confused. I can pass already null. Can you give me a working example how to do that with variables? It seems ansible is not passing the type's properly to the module, even though it does show python's 'None' when using with_items and passing and array of maps.

[Michael DeHaan]

Variables typically stringify when invoked

Something I'm looking to tweak soon.

Consider using "" to mean no value set and you'll be ok.

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[Andy]

So does that mean that the "null" I pass should actually not evaluate to python's "None"? Does that mean my playbook is going to break in the future? What is the spec?

I think I've kind of been misunderstood with this post. The actual issue is shown in detail in the pastebin link (if you have a second, run it'll become clear). So I take it the "null" is just and accidental (undocumented) feature that I'm using? If not, and this is a feature, then I'd consider this behavior a bug since the variable substitution seems to loose the type at some point and it doesn't look like there is a way to get it to behave properly.

FWIW, I just split up the mysql_user in two calls (one which passes "null" directly and one which passes "{{ item.pw }}").

Cheers

[Michael DeHaan]

IMHO, you shouldn't be thinking about a "null" in Ansible.

It's a memory management concept, and Ansible is not a programming language.