We Keep Coding

Slicing paginator.page_range inside a template

I have page_obj in a template which was returned from a ListView view. Now, I wanted to create links to several pages before and after the current page. Therefore, I wanted to slice page_obj.paginator.page_range this way: page_obj.paginator.page_range[page_obj.number-3:page_obj.number+4]. This works in django shell but for some reason when I did it a template, there is a Template Syntax Error, Could not parse the remainder: '[page_obj.number-3:page_obj.number+4]' from 'page_obj.paginator.page_range[page_obj.number-3:page_obj.number+4]'. Is there a workaround for this case?
P.S. I know I can do it using the whole page_obj.paginator.page_range and then using if statements to check if a page is in the required range, but I thought it's a bit inefficient.

As stated in my comment Django Template Language does not include normal python syntax. The reason for this is Django aims to separate the logic and design of the website. If there is need to perform somewhat complicated logic you either need to use template tags or filters.
For your need either an inclusion tag would work or a simple filter that would take the page_range and return a sliced version of it. A template filter here would not be very useful considering we can only pass one argument to it, meaning it would not be very customizable. Let's assume that your pagination would look very similar or perhaps you would pass the template you use to the tag.
Firstly you need to create a templatetags sub-package in your app and then in that you would add files (e.g. pagination_tags.py) which would contain your tags. The layout would be something like:
your_app/
__init__.py
models.py
templatetags/
__init__.py
pagination_tags.py
views.py
Now in your file pagination_tags.py you want to write your tags. As a reference you may read the howto on Custom template tags and filters in the documentation.
Firstly we declare register which is an instance of template.Library. After which we would write our template tags / filters. We will use an inclusion_tag:
from django import template
register = template.Library()
#register.inclusion_tag('pagination_tag.html')
def show_pagination(page_obj, **kwargs):
left = kwargs.get('left', 3)
right = kwargs.get('right', 4)
pages_iter = page_obj.paginator.page_range[page_obj.number - left:page_obj.number + right]
template = kwargs.get('template', 'default_pagination_template.html')
return {**kwargs, 'page_obj': page_obj, 'pages_iter': pages_iter, 'template': template}
Now we will have a simple template named pagination_tag.html that will simply extend the template name either passed as a keyword argument or default_pagination_template.html:
{% extends template %}
Now in default_pagination_template.html or any other template we can use all the variables in the dictionary that our function show_pagination returns:
{% for page_num in pages_iter %}
Display page links here, etc.
{% endfor %}
You can modify this implementation as per your needs. I will also leave the design and implementation of default_pagination_template.html upto you.
Now in your template where you want to use this, first we will load these tags. Then we will use them:
{% load pagination_tags %}
...
{% show_pagination page_obj left=5 right=6 template="some_custom_template.html" %}

Django: efficient template/string separation and override

I have a generic Django view that renders a template. The template is in an app which other projects will use. Importing projects will typically subclass the View the app provides. The View has a default template, which does a job with generic wording.
99% of the time, subclassing Views will want to only change the text, so rather than make them duplicate the template for the sake of altering non-markup wording, i'm looking for a way to allow users of the class to replace wording in the template in the most efficient way.
Options explored so far:
template partials containing only the text which using apps can override (magic, a lot of user work)
A template_strings method on the view which provides a dict of strings which end up in the template context which subclasses can override
Using (abusing?) the translation system such that the app provides default english translations and using code can provide their own translations instead (not actually worked this one out yet, just an idea)
Doing the above template_strings through AppConfig, but this seems ... yucky like it may get very unweildy with a lot of English strings. If doing this I would create a context-like setup so you don't have to re-declare all strings
Seems like it should be a solved problem to subclass a view which does a complete job and just provide alternate strings for text. Is there a better method than the above? Convention? Something I am missing?
(django 1.11 Python 3.6.2)

You can either inherit TemplateView or add ContextMixin to your view, and then override the get_context_data function like this:
from django.views.generic import TemplateView
class BaseView(TemplateView):
template_name = "common.html"
class SubView(BaseView):
def get_context_data(self, **kwargs):
context = super(SubView, self).get_context_data(**kwargs)
context['content'] = "Some sub view text"
return context
Update: Use template overriding
If you want to separate the text out, this is the better way to go
To allow easily and DRY override template across apps, you might need to install this package (Some other detail here)
We define it similarly as above, but change the template_name instead:
from django.views.generic import TemplateView
class BaseView(TemplateView):
template_name = "main.html"
# on another app
class SubView(BaseView):
template_name = "sub_view.html"
Then the magic is you can extends and override block of the BaseView template like this:
base_app/templates/main.html
<p>I'm Common Text</p>
{% block main %}
<p>I'm Base View</p>
{% endblock %}
sub_app/templates/sub_view.html
{% extends "base_app:main.html" %}
{% block main %}
<p>I'm Sub View</p>
{% endblock %}
The result would be:
<p>I'm Common Text</p>
<p>I'm Sub View</p>

Afaik you covered the options pretty well. My example is probably just a variant of the the template strings but maybe it helps anyway...
class DefaultStringProvider():
TITLE = 'Hello'
DESCRIPTION = 'Original description'
CATEGORY = 'Stuff'
class MyTemplateBaseView(TemplateView):
def get_context_data(self, **kwargs):
return super(MyTemplateBaseView, self).get_context_data(
provider=self.get_string_provider(), **kwargs)
def get_string_provider(self):
return DefaultStringProvider()
class OtherView(MyTemplateBaseView):
template_name = 'welcome.html'
def get_string_provider(self):
p = DefaultStringProvider()
p.TITLE = 'Hello'
p.DESCRIPTION = 'New description'
return p
The idea is to have a default string provider and the base view populates the context with it through get_string_provider().
It will at least be quite clear which strings can be overridden for a user extending the base class and it will not interfere with translations.

How to render a Jinja2 macro from a view callable?

I have some macros defined that are called from several templates.
For example, the Product page has a Review section that uses the macros defined in 'helpers/review.jinja2' to print each review. The 'helpers/review.jinja2' file has this two macros:
{% macro render_review(request,review) -%}
{% macro render_review_comment(request,comment) -%}
When someone submits a new review, via ajax, I want to return the rendered review in order to append the content to the Review section.
Right now, I have an intermediate template 'review/review.jinja2' that looks like this:
{% import 'helpers/review.jinja2' as review_helper %}
{{ review_helper.render_review(request,review) }}
This template is rendered from the view:
#view_config(route_name='review.add_review', renderer='review/review.jinja2')
def add_review(request):
return dict(review=my_new_review)
But I hope there is a better way to do this. So, is it possible to render a macro defined in a template?
Thanks

The solution can actually be found in another one of Armin's projects - Flask implements a get_template_attribute method (see here for the source of the method). This points us at Jinja2's Template class, more specifically, the Template class' module attribute.
I don't know if Pyramid's default renderer for Jinja2 exposes that functionality for you, but it should be possible to create and register a custom renderer if the default one does not let you do something like this (entirely theoretical):
#view_config(route_name='review.add_review',
renderer='helpers/review.jinja2:render_review')
def add_review(request):
return dict(review=my_new_review)

This method was suggested elsewhere, it helped me:
#app.route("/test")
def test_view():
t = app.jinja_env.get_template('macros.html')
mod = t.make_module({'request': request})
return mod.my_macro()
Render Jinja2 macro without bothering what's in the rest of the template

How to show widgets on pages in Flask?

How can I create a widget on the site, such as login forms, dynamic menu (items taken from the database), site statistics?
I know that you can render a template that will extend out of a base template. And in the base template you can create these widgets.
But I do not know how to move the logic from the base template to my code. For example, the selection data for the block. Such actions certainly can be done in the template, but it would be a poor method in my opinion.
Sorry for my bad English. If you can not understand, I'll try to rephrase.

You would use a python library called WTForms. It helps you write code for creating forms and other widgets backed by database which you can render using jinja2 templates.
class YourForm(Form):
your_field1 = TextField()
....
your_fieldn = SubmitField()
#app.route('/')
def view():
form=YourForm()
return render_template('your.html', form=form)
In your.html
<form >
{{ form.your_field1 }}
....
{{ form.your_fieldn }}
</form>
Check out this flask pattern for form validation and rendering to know more about it.
Edit: To create global variables available to all templates,there are two ways:
You can use global dict of jinja environment.
This is the code:
app.jinja_env.globals.update({'variable':1})
You can use ContextProcessor. Code:
#app.context_processor
def inject_variable():
return dict(variable=1)
Now you can access variable in any template of your app.

Automatically add a variable into context on per-application basis in Django?

I want to add a context variable in Django, so that I could define its value on per-application basis, or leave it empty.
Example:
apps/someapp/views.py:
def_context_var('app_name', 'Calendar')
templates/base.html:
{% if app_name %}You are in {{ app_name }} app.{% endif %}
....
{% if app_name %}Subsections of {{ app_name }}: ...{% endif %}
I considered the following:
Declare a variable in the app (in a view, or in URLs), and make a context processor. But I can't understang how to extract that var given the request object.
Put decorators on views. Hm, I don't like the idea: too much boilerplate or duplicated code.
#1 but nicer: make methods (like in the example above) that are executed on server restart, write the data into a dict, then a context processor somehow (how?) gets the application name and extracts the data from the dict. Where do I put the method, the dict, how does the context processor know where the view object is in?

You can call resolve(request.path) in a context processor to resolve the current url. See the django documentation on resolve for its return values, especially app_name.