How to repeat a “block” in a django template
https://stackoverflow.com/questions/511067
-
21-08-2019 - |
italiano
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I want to use the same {% block %} twice in the same django template. I want this block to appear more than once in my base template:
# base.html
<html>
<head>
<title>{% block title %}My Cool Website{% endblock %}</title>
</head>
<body>
<h1>{% block title %}My Cool Website{% endblock %}</h1>
</body>
</html>
And then extend it:
# blog.html
{% extends 'base.html' %}
{% block title %}My Blog{% endblock %}
# pictures.html
{% extends 'base.html' %}
{% block title %}My Pictures{% endblock %}
# cats.html
{% extends 'base.html' %}
{% block title %}My Cats{% endblock %}
I will get an exception, as Django wants the block to appear only once:
TemplateSyntaxError at /
'block' tag with name 'title' appears more than once
A quick and dirty solution would be duplicating the block title into title1 and title2:
# blog.html
{% extends 'base.html' %}
{% block title1 %}My Blog{% endblock %}
{% block title2 %}My Blog{% endblock %}
But this is a violation of the DRY principle. It would be very difficult as I have a lot of inheriting templates, and also because I don't wanna go to hell ;-)
Is there any trick or work-around to this problem? How can I repeat the same block in my template, without duplicating all the code?
Solution
I think that use of the context processor is in this case an overkill. You can easily do this:
#base.html
<html>
<head>
<title>{% block title %}My Cool Website{% endblock %}</title>
</head>
<body>
{% block content %}{% endblock %}
</body>
</html>
and then:
# blog.html
{% extends 'base.html' %}
{% block content %}
<h1>{% block title %}My Blog{% endblock %}</h1>
Lorem ipsum here...
{% endblock %}
and so on... Looks like DRY-compatible.
OTHER TIPS
Use the Django template macros plugin:
http://www.djangosnippets.org/snippets/363/ (django < 1.4)
or
https://gist.github.com/1715202 (django >= 1.4)
Then,
# base.html
{% macro title %}
{% block title %}My Cool Website{% endblock %}
{% endmacro %}
<html>
<head>
<title>{% usemacro title %}</title>
</head>
<body>
<h1>{% usemacro title %}</h1>
</body>
</html>
and
# blog.html
{% extends 'base.html' %}
{% block title %}My Blog{% endblock %}
You probably don't actually want to use a block but rather to just use a variable:
# base.html
<html>
<head>
<title>{{ title|default:"My Cool Website" }}</title>
</head>
<body>
<h1>{{ title|default:"My Cool Website" }}</h1>
</body>
</html>
You then set the title through the context.
you can use {% include subtemplate.html %} more than once. it's not the same as blocks, but does the trick.
Here's a way I discovered when trying to do the same thing myself:
# base_helper.html
<html>
<head>
<title>{% block _title1 %}{% endblock %}</title>
</head>
<body>
<h1>{% block _title2 %}{% endblock %}</h1>
</body>
</html>
# base.html
{% extends "base_helper.html" %}
# Copy title into _title1 & _title2, using "My Cool Website" as a default.
{% block _title1 %}{% block _title2 %}{% block title %}My Cool Website{% endblock %}{% endblock %}{% endblock %}
Requires an extra file unfortunately, but doesn't require you to pass the title from the view.
There are some discussion here: http://code.djangoproject.com/ticket/4529 Obviously django core team reject this ticket because they think this is not a common used scenario, however I disagree.
repeat block is simple and clean implementation for this: https://github.com/SmileyChris/django-repeatblock
template macros is another one, however the author mentioned it's not carefully tested: http://www.djangosnippets.org/snippets/363/
I used repeatblock.
As an update for anyone coming across this, I've taken the snippet mentioned above and turned it into a template tag library, django-macros, makes the macros more powerful and also implements a repeated block pattern explicitly: django-macros.
Here is a lightweight solution similar to the above do_set and do_get template tag answer. Django allows you to pass the entire template context into a tag which can allow you to define a global variable.
base.html:
<!DOCTYPE html>
<html lang="en">
<head>
{% block head %}
<title>{{ title }}</title>
{% endblock %}
</head>
<body>
<h1>{{ title }}</h1>
</body>
</html>
page.html:
{% extends "base.html" %}
{% block head %}
{% define 'title' 'Homepage | title' %}
{{ block.super }}
{% endblock %}
custom tag (got the idea here: https://stackoverflow.com/a/33564990/2747924):
@register.simple_tag(takes_context=True)
def define(context, key, value):
context.dicts[0][key] = value
return ''
Also don't forget to {% load %} your custom tags or add them to the template options builtins list so you don't have to load them in every template. The only limitation to this approach is the {% define %} has to be called from within a block tag because child templates only render block tags that match the parent tags. Not sure if there is a way around that. Also make sure the define call comes before you try to use it obviously.
Building on Van Gale's suggestion, you could create get and set tags by adding the following to your templatetags.py file:
register = template.Library()
Stateful = {}
def do_set(parser, token):
_, key = token.split_contents()
nodelist = parser.parse(('endset',))
parser.delete_first_token() # from the example -- why?
return SetStatefulNode(key,nodelist)
class SetStatefulNode(template.Node):
def __init__(self, key, nodes):
Stateful[key] = nodes
def render(self, context):
return ''
register.tag('set', do_set)
def do_get(parser, token):
tag_name, key = token.split_contents()
return GetStatefulNode(key)
class GetStatefulNode(template.Node):
def __init__(self, key):
self.key = key
def render(self, context):
return ''.join( [x.render(context) for x in Stateful[self.key]] )
register.tag('get', do_get)
Then set values in one template via {% set foo %}put data here{% endset %} and get them via {% get foo %} in another.
I too have come across the same need for a repeated {% block %} in my template files. The issue is that I want a Django {% block %} to be used in either case of a Django conditional, and I want the {% block %} to be over-writable by subsequent files that may extend the current file. (So in this case, what I want is definitely more of a block than a variable because I'm not technically re-using it, it just appears on either end of a conditional.
The Problem:
The following Django template code will result in a Template Syntax Error, but I think it's a valid "want" to have a defined {% block %} re-used in a conditional (IE, why is the Django parser validating syntax on BOTH ends of a conditional, shouldn't it only validate the TRUTHY condition?)
# This example shows a {{ DEBUG }} conditional that loads
# Uncompressed JavaScript files if TRUE
# and loads Asynchronous minified JavaScript files if FALSE.
# BASE.html
{% if DEBUG %}
<script src="{{MEDIA_URL}}js/flatfile.1.js"></script>
<script src="{{MEDIA_URL}}js/flatfile.2.js"></script>
<script src="{{MEDIA_URL}}js/flatfile.3.js"></script>
<script type="text/javascript">
{% block page_js %}
var page = new $site.Page();
{% endblock page_js %}
</script>
{% else %}
<script type="text/javascript">
// load in the PRODUCTION VERSION of the site
// minified and asynchronosly loaded
yepnope([
{
load : '{MEDIA_URL}}js/flatfiles.min.js',
wait : true,
complete : function() {
{% block page_js %} // NOTE THE PAGE_JS BLOCK
var page = new $site.Page();
{% endblock page_js %}
}
}
)];
</script>
{% endif %}
# ABOUT.html
{% extends 'pages/base.html' %}
{% block page_js %}
var page = new $site.Page.About();
{% endblock page_js %}
The Solution:
You can use an {% include %} to conditionally insert a {% block %} more than once. This worked for me because the Django syntax checker includes only the TRUTHY {% include %}. See the result below:
# partials/page.js
{% block page_js %}
var page = new $site.Page();
{% endblock %}
# base.html
{% if DEBUG %}
<script src="{{MEDIA_URL}}js/flatfile.1.js"></script>
<script src="{{MEDIA_URL}}js/flatfile.2.js"></script>
<script src="{{MEDIA_URL}}js/flatfile.3.js"></script>
<script type="text/javascript">
{% include 'partials/page_js.html' %}
</script>
{% else %}
<script type="text/javascript">
yepnope([
{
load : '{MEDIA_URL}}js/flatfiles.min.js',
wait : true,
complete : function() {
{% include 'partials/page_js.html' %}
}
}
)];
</script>
{% endif %}
There are two easy solutions for this.
The easiest is to put your title into a context variable. You would set the context variable in your view.
If you are using something like generic views and don't have a views.py for pictures, cats, etc. then you can go the way of a custom template tag that sets a variable in the context.
Going this route would enable you to do something like:
{% extends "base.html" %}
{% load set_page_title %}
{% page_title "My Pictures" %}
...
Then in your base.html:
...
{% block title %}{{ page_title }}{% endblock %}
...
<h1>{{ page_title }}</h1>
I use this answer to keep things dry.
{% extends "base.html" %}
{% with "Entry Title" as title %}
{% block title %}{{ title }}{% endblock %}
{% block h1 %}{{ title }}{% endblock %}
{% endwith %}
In twig you can make this like:
# base.html
<html>
<head>
<title>{{ block('title') }}</title>
</head>
<body>
<h1>{{ block('title') }}</h1>
</body>
</html>
# blog.html
{% extends 'base.html' %}
{% block title %}My Blog{% endblock %}
# pictures.html
{% extends 'base.html' %}
{% block title %}My Pictures{% endblock %}
# cats.html
{% extends 'base.html' %}
{% block title %}My Cats{% endblock %}
