Code should be readable.

Recently, I had to make some changes to some XML that had been written in a Django template.  To avoid the xml being rendered by the browser as HTML, the code had been manually escaped, thus making the code rather unreadable.

Sorry, no views

The various documentation templates were being rendered using direct_to_template so I couldn’t move the XML to a view and let Django’s autoescaping take over.  Besides, the XML is legitamately part of the static content of the page and shouldn’t be in the view.

Custom filters can be very misleading

So I decided to write a custom filter to escape the XML as needed.  But I kept running into this error:

‘my_filter’ is not a valid tag library: Could not load template library from django.templatetags.doc_code, No module named my_filter

Which made me think I had a path issue, or a misplaced file, or a missing __init__.py.  But all my initial guesses checked out.  Turns out that django spits out a ‘No module’ error when there are errors in the filter code.  Very misleading.

Now it’s looking good

So the final result is a django  template that looks like this:

<p>Here's some XML:</p>
{% filter xmldoc %}
<children>
    <child>Koes</child>
    <child>Chris</child>
</children>
{% endfilter %}

And the custom filter looks like this:

from django.template import Library
from django.template.defaultfilters import stringfilter
from xml.sax.saxutils import escape
 
register = Library()
 
@register.filter
@stringfilter
def xmldoc(value):
    return escape(value).strip()
xmldoc.is_safe = True

Now the XML is readable to the users and the developers.

My sources

• Django custom filters
• I was missing an import in my filter