If-else and for loops not working in HTML for new XBlock

Development
1

Hi!
I’m trying to pass data from python file to HTML file, but standard syntax is not supported, HTML file code below

<p>EdlyCarouselXBlock: count is now
    <span class='count'>{self.count}</span> (click me to increment).
    {{ self.count }}
    {% if self.count%}
    <p>Simple If</p>
    {%endif%}
</p>
<p id="decrement">(click me to Decrement).</p>
</div>

It is supporting a single bracket to access values {self.name} , for loops & if-else it throws an error.

error
error1958×730 146 KB

Tried using python 3.6.5 & 3.8.0, the same issue on both versions, any help would be appreciated.
Same issue in the lms/cms as well.
cc: @regis @braden

2

Solve the issue, posting the solution for future references.
Default xblock is created without using Django templating so we need to configure it manually.

Following default student_view function is added

def student_view(self, context=None):
    """
    The primary view of the SampleXBlock, shown to students
    when viewing courses.
    """
    html = self.resource_string("static/html/sample.html")
    frag = Fragment(html.format(self=self))
    frag.add_css(self.resource_string("static/css/sample.css"))
    frag.add_javascript(self.resource_string("static/js/src/sample.js"))
    frag.initialize_js('SampleXBlock')
    return frag

so in order to involve Django template rendering make the following changes.
include template and context

from django.template import Context, Template

# Add this method in your xblock class

def render_template(self, template_path, context={}):
    template_str = self.resource_string(template_path)
    template = Template(template_str)
    return template.render(Context(context))

def student_view(self, context=None):
    """
    The primary view of the SampleXBlock, shown to students
    when viewing courses.
    """
    frag = Fragment()

    html = self.render_template("static/html/sample.html", {'count': self.count})
    frag.add_content(html)
    frag.add_css(self.resource_string("static/css/sample.css"))
    frag.add_javascript(self.resource_string("static/js/src/sample.js"))
    frag.initialize_js('SampleXBlock')
    return frag
3

It looks like you might be trying to use Django template syntax, but your XBlock code is trying to render it as a Mako template (EDIT: oh, not even mako template, from your own answer I see it was plain python format). They are two different template languages used Open edX to render HTML from python.

I strongly recommend using Django templates instead of Mako, so instead of calling mako.lookup.TemplateLookup(...).get_template(...).render_unicode(...), I’d suggest calling xblockutils.resources.ResourceLoader.render_django_template().

By the way, using render_django_template() (and passing in i18n_service=self.runtime.service(self, 'i18n') as a keyword argument) is the only easy way to get translation files (i18n/l10n) that come with your XBlock to be used by your template, instead of the default platform strings.

All that said, if you can avoid using server-side templates at all, and use JavaScript-based templates (like React) instead, even better!

1 Like
4

Thank you for quick response, I was able to solve it and you are right I was missing Django Template reference.