Controlling whitespace in Jinja2 templates: Difference between revisions
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From the Jinja2 documentation, there are two options to control whitespace in Jinja templates: | From the Jinja2 documentation, there are two options to control whitespace in Jinja templates: | ||
* <code>trim_blocks</code> | |||
* <code>lstrip_blocks</code> | *<code>trim_blocks</code> | ||
*<code>lstrip_blocks</code> | |||
But actually, there's more to it. [https://jinja.palletsprojects.com/en/3.1.x/templates/ The "Template Designer Documentation"] specifically for [https://jinja.palletsprojects.com/en/3.1.x/templates/#whitespace-control whitespace control] is inadequate. That's why I wrote this article. | But actually, there's more to it. [https://jinja.palletsprojects.com/en/3.1.x/templates/ The "Template Designer Documentation"] specifically for [https://jinja.palletsprojects.com/en/3.1.x/templates/#whitespace-control whitespace control] is inadequate. That's why I wrote this article. | ||
== Jinja in Ansible == | ==Jinja in Ansible== | ||
In [[Ansible]]'s Template module, you can see in the source code | In [[Ansible]]'s Template module, you can see in the source code | ||
* [https://github.com/search?q=repo%3Aansible%2Fansible%20trim_blocks&type=code trim_blocks defaults to true] | |||
* [https://github.com/search?q=repo%3Aansible%2Fansible%20lstrip_blocks&type=code lstrip_blocks defaults to false] | *[https://github.com/search?q=repo%3Aansible%2Fansible%20trim_blocks&type=code trim_blocks defaults to true] | ||
*[https://github.com/search?q=repo%3Aansible%2Fansible%20lstrip_blocks&type=code lstrip_blocks defaults to false] | |||
But what does this mean? What do these options do? And how do I use them in my Ansible templates? | But what does this mean? What do these options do? And how do I use them in my Ansible templates? | ||
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== In the task == | ==In the task== | ||
In at least v2.9 of Ansible, the Template module has options to specify both. | In at least v2.9 of Ansible, the Template module has options to specify both. | ||
== In the template file == | *[https://docs.ansible.com/ansible/2.9/modules/template_module.html 2.9 docs for the template module] [] | ||
*[https://docs.ansible.com/ansible/latest/modules/template_module.html latest docs for the template module] | |||
**[https://docs.ansible.com/ansible/latest/collections/ansible/builtin/template_module.html#parameter-lstrip_blocks parameter lstrip_blocks] | |||
**[https://docs.ansible.com/ansible/latest/collections/ansible/builtin/template_module.html#parameter-trim_blocks parameter trim_blocks] | |||
==In the template file== | |||
As the '''very first line''' of your template file, you can use a magic comment directive to control the behavior of the Ansible Template module | As the '''very first line''' of your template file, you can use a magic comment directive to control the behavior of the Ansible Template module | ||
<code>#jinja2: trim_blocks: "true", lstrip_blocks: "true"</code><ref>It's unclear whether the boolean value(s) to be quoted. I believe it was a bug that is now fixed - meaning they can be bare.</ref> | <code>#jinja2: trim_blocks: "true", lstrip_blocks: "true"</code><ref>It's unclear whether the boolean value(s) to be quoted. I believe it was a bug that is now fixed - meaning they can be bare.</ref> | ||
== By hand == | ==By hand== | ||
If you're confused about Variable notation and how those are defined in templates, see https://jinja.palletsprojects.com/en/3.1.x/templates/#variables | If you're confused about Variable notation and how those are defined in templates, see https://jinja.palletsprojects.com/en/3.1.x/templates/#variables | ||
== Debugging == | ==Debugging== | ||
Just put <code>{% debug %}</code> somewhere in your template file. | Just put <code>{% debug %}</code> somewhere in your template file. | ||
{{References}} | <br /> | ||
== More == | |||
Bloomreach Engagement is a commercial Web product that uses Jinja for templating. So they have a pretty good [https://documentation.bloomreach.com/engagement/docs/jinja-syntax reference guide].{{References}} | |||
[[Category:Ansible]] | [[Category:Ansible]] | ||
[[Category:Templating]] | [[Category:Templating]] | ||
[[Category:Python]] | [[Category:Python]] | ||
Revision as of 09:07, 12 April 2024
For background perspective, Jinja is used as a templating system by various Python projects like Django, Flask, or Ansible.
From the Jinja2 documentation, there are two options to control whitespace in Jinja templates:
trim_blockslstrip_blocks
But actually, there's more to it. The "Template Designer Documentation" specifically for whitespace control is inadequate. That's why I wrote this article.
Jinja in Ansible[edit]
In Ansible's Template module, you can see in the source code
But what does this mean? What do these options do? And how do I use them in my Ansible templates?
trim blocks means the first newline after a block is removed (block, not variable tag!)
lstrip blocks [1] means leading spaces and tabs are stripped from the start of a line to a block.
So, I can read words, but without context nor further example and explanation, I can't decode what "from the start of a line to a block" means.
In the task[edit]
In at least v2.9 of Ansible, the Template module has options to specify both.
In the template file[edit]
As the very first line of your template file, you can use a magic comment directive to control the behavior of the Ansible Template module
#jinja2: trim_blocks: "true", lstrip_blocks: "true"[2]
By hand[edit]
If you're confused about Variable notation and how those are defined in templates, see https://jinja.palletsprojects.com/en/3.1.x/templates/#variables
Debugging[edit]
Just put {% debug %} somewhere in your template file.
More[edit]
Bloomreach Engagement is a commercial Web product that uses Jinja for templating. So they have a pretty good reference guide.== References ==
- ↑
lstripstands for "left strip". It is a function in Python, as well as R and Ruby. Likeltrimin PHP ortrimStartin JavaScript. nb. Jinja also has a built-in filter namedtrimthat is used to strip characters from the beginning and end of a string. - ↑ It's unclear whether the boolean value(s) to be quoted. I believe it was a bug that is now fixed - meaning they can be bare.
