Remove unnecessary whitespace from Jinja rendered template
Question:
I’m using curl to watch the output of my web app.
When Flask and Jinja render templates, there’s a lot of unnecessary white space in the output.
It seems to be added by rendering various components from Flask-WTF and Flask-Bootstrap.
I could strip this using sed, but is there a way to control this from Jinja?
Answers:
Jinja has multiple ways to control whitespace. It does not have a way to prettify output, you have to manually make sure everything looks "nice".
The broadest solution is to set trim_blocks and lstrip_blocks on the env.
app.jinja_env.trim_blocks = True
app.jinja_env.lstrip_blocks = True
If you want to keep a newline at the end of the file, set strip_trailing_newlines = False.
You can use control characters to modify how the whitespace around a tag works. - always removes whitespace, + always preserves it, overriding the env settings for that tag. The - character can go at the beginning or end (or both) of a tag to control the whitespace in that direction, the + character only makes sense at the beginning of a tag.
{%- if ... %} strips before{%- if ... -%} strips before and after{%+ if ... %} preserves before{%+ if ... -%} preserves before and strips after- remember that
{% endif %} is treated separately
The control characters only apply to templates you write. If you include a template or use a macro from a 3rd party, however they wrote the template will apply to that part.
To collapse whitespace before and after a block:
{%- if form.message -%} //trims before
{{ form.message }}
{%- endif -%} // trims after
I’m using curl to watch the output of my web app.
When Flask and Jinja render templates, there’s a lot of unnecessary white space in the output.
It seems to be added by rendering various components from Flask-WTF and Flask-Bootstrap.
I could strip this using sed, but is there a way to control this from Jinja?
Jinja has multiple ways to control whitespace. It does not have a way to prettify output, you have to manually make sure everything looks "nice".
The broadest solution is to set trim_blocks and lstrip_blocks on the env.
app.jinja_env.trim_blocks = True
app.jinja_env.lstrip_blocks = True
If you want to keep a newline at the end of the file, set strip_trailing_newlines = False.
You can use control characters to modify how the whitespace around a tag works. - always removes whitespace, + always preserves it, overriding the env settings for that tag. The - character can go at the beginning or end (or both) of a tag to control the whitespace in that direction, the + character only makes sense at the beginning of a tag.
{%- if ... %}strips before{%- if ... -%}strips before and after{%+ if ... %}preserves before{%+ if ... -%}preserves before and strips after- remember that
{% endif %}is treated separately
The control characters only apply to templates you write. If you include a template or use a macro from a 3rd party, however they wrote the template will apply to that part.
To collapse whitespace before and after a block:
{%- if form.message -%} //trims before
{{ form.message }}
{%- endif -%} // trims after