Stripping whitespace in jinja2 & flask...why do I still need the minus sign?

Question

In my init.py file I have:

app.jinja_env.trim_blocks = True
app.jinja_env.lstrip_blocks = True

I expect in my jinja2 template that whitespace will be trimmed, so that:

<div>
{% if x == 3 %}
<small>{{ x }}</small>
{% endif %}
</div>

will render as:

<div>
<small>3</small>
</div>

Instead, I get extra whitespace:

<div>

<small>3</small>

</div>

Why doesn't trim_blocks and lstrip_blocks trim the whitespace?

Answer 1

It seems like your environment settings are not set before jinja2 loads your template.

class jinja2.Environment([options])

... Instances of this class may be modified if they are not shared and if no template was loaded so far. Modifications on environments after the first template was loaded will lead to surprising effects and undefined behavior.

http://jinja.pocoo.org/docs/dev/api/#jinja2.Environment

Check the order/structure of your code to see how the environment settings vs templates are loaded.

As an aside, jinja2's whitespace control does work as expected without the complexity of environments and loading:

import jinja2

template_string = '''<div>
{% if x == 3 %}
<small>{{ x }}</small>
{% endif %}
</div>
'''
# create templates
template1 = jinja2.Template(template_string)
template2 = jinja2.Template(template_string, trim_blocks=True)

# render with and without settings
print template1.render(x=3)
print '\n<!-- {} -->\n'.format('-' * 32)
print template2.render(x=3)

---

<div>

<small>3</small>

</div>

<!-- -------------------------------- -->

<div>
<small>3</small>
</div>

I've not used jinja2, but after scanning the docs, loading order seems to be suspect.