Develop Reference

'for' statements should use the format 'for x in y': while iterating over value retrieved from dictionary using django template

I have a context dictionary entry objectives that maps objective query objects to a list of tests that belong to that objective. Example code:
objectives = Objective.objects.filter(requirement=requirement)
context_dict["requirements"][requirement] = objectives
for objective in objectives:
tests = Test.objects.filter(objective=objective)
context_dict["objectives"][objective] = tests
In my django html template, I iterate over objectives and display them. I then want to iterate over the tests that belong to these objectives. When I do this:
{% for test in {{ objectives|get_item:objective }} %}
I get a TemplateSyntaxError: 'for' statements should use the format 'for x in y':
In the application/templatetags directory, I have:
from django.template.defaulttags import register
...
#register.filter
def get_item(dictionary, key):
return dictionary.get(key)
If instead I make {{ objectives|get_item:objective }} a JS variable, I see that it does indeed produce a list, which I should be able to iterate over. Of course, I can't mix JS variables and the django template tags, so this is only for debugging:
var tests = {{ objectives|get_item:objective }}
var tests = [<Test: AT399_8_1>, <Test: AT399_8_2>, <Test: AT399_8_3>, <Test: AT399_8_4>, <Test: AT399_8_5> '...(remaining elements truncated)...']
How do I iterate over this list in the django template tag?

You cannot user {{...}} inside the {%...%}
What you can try is changing your filter to an assignment tag and using that value in the loop
#register.assignment_tag
def get_item(dictionary, key):
return dictionary.get(key)
And then in your template use it as
{% get_item objectives objective as tests %}
{% for test in test %}
....
{% endfor %}
Instead of all this if your models are proper with foreign keys I would do something like
{% for objective in requirement.objective_set.all %}
{% for test in objective.test_set.all %}
....
{% endfor %}
{% endfor %}
In my context I would pass only the requirement

You already have an answer, but note that dropping the {{ }} tags and keeping everything else the same would have worked fine.
{% for test in objectives|get_item:objective %}

**This is Right Answer for Using Django if else and for loop **
Note :- We Have to Put Key in " " string (Double quotes) some time produce an error so That is good way bcz i faced that problem whwn i Learned
{% if 'numbers'|length > 0 %}
{% for i in numbers %}
{% if i > 20 %}
{{i}}
{% endif %}
{% endfor %}
{% else %}
Empty
{% endif %}

Django - create custom tag to acces variable by index in template

I have a HTML template in django. It get's two variables: list of categories (queryset, as it it returned by .objects.all() function on model in django) and dictionary of contestants. As a key of the dictionary, I'm using id of category, and value is list of contestats.
I want to print name of the category and then all the contestants. Now I have this:
{% for category in categories_list %}
<h1>category.category_name</h1>
{% for contestant in contestants_dict[category.id] %}
{{ contestant }} </br>
{% endfor %}
{% endfor %}
However, when I run it, I get error:
TemplateSyntaxError at /olympiada/contestants/
Could not parse the remainder: '[category.id]' from 'contestants_dict[category.id]'
What I know so far is that I can't use index in template. I thought that {% something %} contains pure Python, but it shoved up it's just a tag. I know that I have to create my own simple_tag, but I don't know how. I read the docs Writing custom template tags, but there is such a little information and I wasn't able to fiqure out how to create (and mainly use in a for loop) a tag, that will take dict, key and return the value. What I tried is:
templatetags/custom_tags.py:
from django import template
register = template.Library()
#register.simple_tag
def list_index(a, b):
return a[b]
and in template:
{% for contestant in list_index contestants_dict category.id %}
But I get TemplateSyntaxError.
Could you please explain/show me how to create the tag, or is there a better way to do this?
Thanks.
//EDIT:
I managed to do it this way:
{% list_index contestants_list category.id as cont %}
{% for contestant in cont %}
it works, but it takes 2 lines and I need to create another variable. Is there any way to do it without it?

If you don't want 2 lines like that you should be able to use a filter i think
#register.filter
def list_index(a, b):
return a[b]
Then the usage like this
{% for contestant in contestants_dict|list_index:category.id %}
{{ contestant }} </br>
{% endfor %}

Modify django templates to check for values in a dict

I have the following Django template.
{% load custom_tags %}
<ul>
{% for key, value in value.items %}
<li> {{ key }}: {{ value }}</li>
{% endfor %}
I need to check for the value and do some modifications.
If the value is True , instead of value I have to print Applied , else if it False I need to print Not Applied.
How to achieve that?

Very simple if-else clause here. Take a look at the django template docs to familiarize yourself with some of the common tags.
{% if value %}
APPLIED
{% else %}
NOT APPLIED
{% endif %}
You asked how to do this as a filter... I'm not sure why, but here is it:
In your app's templatetags directory create a file called my_tags.py or something and make the contents
from django import template
register = template.Library()
#register.filter
def applied(value):
if value:
return 'Applied'
else:
return 'Not applied'
Then in your template make sure to have {% load my_tags %} and use the filter with {{ value|applied }}

Django filter field on the context processor

I want to filter a result of a field in django in an html file.
Something like this
{{ model.field where id = 2 }}
I've been looking for in django docs but i only could find a way to do it on the views.py.
I also so something like javascript when u write a "|" simbol after the request but i still couldnt archieve it

You can use the {% if %} template tag. So:
{% if model.field == 2 %}
# do something
{% endif %}
Here is the official documentation:
https://docs.djangoproject.com/en/dev/ref/templates/builtins/#operator
Edit:
If model.field has a value of 2 then it just needs to be the above.
Edit 2:
Without seeing your code, it is hard to tell, but here is how to filter for Users based on Gender in a template:
{% for user in users %}
{% if user.gender == "male" %}
# do something
user.username
{% endif %}
{% endfor %}

Python/Django: Simple Django Template

Hi I am using App Engine/Python to do a simple website. I have some trouble with a Django template problem.
In short, I want to use a "ShortName" to access a "LongName".
The soource code:
LongName={"so":"stackoverflow","su":"superuser"}
ShortName=['so','su']
Then I pass these two parameters to the templates.
In the template I write:
{% for aname in ShortName %}
{{ aname }} stands for {{ LongName.aname }},
{% endfor %}
The output is:
so stands for, su stands for
No error is given. The LongName.aname wont work.
I have no idea whats wrong.

This is trying to access LongName['aname'], not LongName[aname].
You might have to write a custom template tag/filter to get this to work. This Django bug (marked WONTFIX) has a simple implementation:
def get(d, key):
return d.get(key, '')
register.filter(get)
which you would use by
{{ LongName|get:aname }}
after adding it to your app (that SO answer shows how to do it on GAE).
You could also pre-make a variable to loop over in the view, by passing in
# in view
name_abbrevs = [(k, LongName[k]) for k in ShortName]
# in template
{% for short_name, long_name in name_abbrevs %}
{{ short_name }} stands for {{ long_name }}
{% endif %}
If you really don't want to add a template tag -- which isn't that bad! you just make one file! :) -- or pass in an extra variable, Vic's approach will let you do this without touching the Python files at all. As he mentions, it involves a lot of pointless iteration, but it'll work fine for small lists.

Django templates have a drawback here. I've been in the same situation before. What you have to do is iterate over all the keys in LongName, and check if the key you're looking for matches the ShortName. Here you go:
{% for aname in ShortName %}
{% for short_version, long_version in LongName %}
{% if aname == short_version %}
{{ aname }} stands for {{ long_version }},
{% endif %}
{% endfor %}
{% endfor%}
It's inefficient, and essentially a pointless O(n^2) mechanism. However, there's no better way in pure Django templates to refer to entries of a dict by a variable name.