Question

I m a front end developer, and I ve been trying to get a hang on using Jinja2 effectively. I want to tweak a current site so it has multiple base templates using inheritance, it fully uses block tags to substitute content and override it, and uses macros to support passing of arguments.

My base template contains this code (edited for simplicity):

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
{% from "foo.html" import macro1, macro2, macro3 %}
{% macro base_template(title=none, arg2=none, urls={}, arg3=false) %}
<html>
  <title>{{ title }} | Site.com</title>
  ....
  {{ caller() }}
  ....
</html>
{% endmacro %}

{% block content %}{% endblock %}

And my pages that extend it look like this:

{% extends "base.html" %}
{% block content %}
{% call base_template(title="home", arg2="active", arg3="true") %}
(html code here)
{% endcall %}
{% endblock %}

So basically all the pages extend base, they call a macro and pass arguments to that macro. I don t quite understand it all, but the main point is that this allows default values and a degree of flexibility that doesn t require redefining an entire block: it gives some degree of flexibility and power. Again this is heavily simplified.

The only problem is, this negates my ability to use blocks. Macros are for flexibility, but with blocks, I have the ability to override something entirely, or use it s parents contents and add to it, which I can t do with Macros (at least I don t think). The problem is, I can t wrap things in blocks, else they won t see the values in the macro. For instance, doing this:

{% block title %}<title>{{ title }} | Site.com</title>{% endblock %}

Will fail because it will say title is undefined.

Ultimately I am looking for a way to utilize both the power and organiztional aspects of blocks, but still be able to utilize the logic & terseness of macros. If anyone could give me any help as to how I might go about this problem, I would really appreciate it.

Answer 1

Blocks are only definable at a template s top level. If you extend a template, any values set in the child template using a set tag will be accessible from the template it is extending. For example, if you have a template named layout.html:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
  <title>{{ title }} | Site.com</title>
  ....
  {% block content %}{% endblock content %}
  ....
</html>

And you have this child template, index.html:

{% extends "layout.html" %}
{% set title =  Homepage  %}
{% block content %}
(html code here)
{% endblock content %}

Then the reference to title in the parent would resolve to Homepage . You can do this with any type of variable. For what you re doing, I don t think there is any need for macros - if you take advantage of this feature and place blocks well, you will be able to do pretty much everything you need to do as far as layouts are concerned. I would look at some of the templates used by Plurk Solace, which is written by one of the Jinja2 authors, if you want to get a good idea of when to use various features of Jinja2.

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