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How do minus in django template [duplicate]

It is able to write {{ myval.add:5 }}, {{ myval|add:value }} and even {{ myval|add:-5 }}.
However, I can't find out what I should type to add value * -1 like {{ myval|add:-value }}. This doesn't work, sadly.

You need to use double quotes:
{{ myval|add:"-5" }}
This subtracts five from myval.

The built-in Django template tags/filters aren't all-encompassing, but it's super easy to write your own custom template tags: https://docs.djangoproject.com/en/dev/howto/custom-template-tags/
You could make your own subtract template tag pretty easily:
#register.filter
def subtract(value, arg):
return value - arg

Use django-mathfilters from PyPI: https://pypi.python.org/pypi/django-mathfilters
To install :
$ pip install django-mathfilters
Then add mathfilters in your INSTALLED_APPS.
In template:
{% load mathfilters %}
<ul>
<li>8 + 3 = {{ 8|add:3 }}</li>
<li>13 - 17 = {{ 13|sub:17 }}</li>
{% with answer=42 %}
<li>42 * 0.5 = {{ answer|mul:0.5 }}</li>
{% endwith %}
{% with numerator=12 denominator=3 %}
<li>12 / 3 = {{ numerator|div:denominator }}</li>
{% endwith %}
<li>|-13| = {{ -13|abs }}</li>
</ul>

I recently started working with Django and stumbled upon this one as well: I needed a very simple template loop that stops printing after n times and shows a "more" link to toggle the rest of the items.
With great interest I read the struggle of people trying to understand why this is not being added to the Django default filters (since before 2013). I didn't feel like creating a custom template tag and I kind of found a way to subtract 2 variables using strings and add in combination with with and stringformat
Let's say I have a list of items where I want to print the first 2 and hide the rest, showing how many hidden items are there, eg.
John, Anna and 5 others like this (when given a list of 7 items)
As long as the number of visible items is harcoded in the template (eg. 2), it's possible to add the negative 2 |add:"-2", but I wanted the number of visible items to be a variable as well. The Math-filter library as suggested above doesn't seem up to date (I haven't tested it with Django 2.x).
The trick seems to be to use the add helper to concat the strings "-" with the integer as string, so it can be coerced back to a negative integer in a any consecutive calls to the add helper. This doesn't work however if the value is not a string, so that's where the stringformat helper comes in.
With string value
template posts.html (note how visible is explicitely passed as string - alternative below)
{% for post in posts %}
<h4>{{ post.title }}</h4>
...
{% include 'show_likes.html' with likes=post.likes visible="3" %}
{% endfor %}
template show_likes.html (note the add:0 to make the boolean operator work)
{% with show=visible|default:"2" %}
{% for like in likes %}
{% if forloop.counter <= show|add:0 %}
{% if not forloop.first %},{% endif %}
{{ like.username }}
{% endif %}
{% endfor %}
{% if likes|length > show|add:0 %}
{% with rest="-"|add:show %}
and {{ likes|length|add:rest }} more
{% endwith %}
{% endif %}
like this
{% endwith %}
Alternative with integer
You could just convert your integer to a string in the calling template using |stringformat:"d"
If however the number of visible items you want to show is an integer, you'll have to add a call to stringformat:"d" to have it converted to string
template posts.html
{% for post in posts %}
<h4>{{ post.title }}</h4>
...
{% include 'show_likes.html' with likes=post.likes visible=3 %}
{% endfor %}
template show_likes.html
{% with show=visible|default:2 %}
{% with show_str=show|stringformat:"d" %}
{% for like in likes %}
{% if forloop.counter <= show %}
{% if not forloop.first %},{% endif %}
{{ like.username }}
{% endif %}
{% endfor %}
{% if likes|length > show|add:0 %}
{% with rest="-"|add:show_str %}
and {{ likes|length|add:rest }} more
{% endwith %}
{% endif %}
{% endwith %}
{% endwith %}
Since I'm a very beginner with Django and Python, I'm pretty sure this approach is far worse than actually creating a custom helper! So I'm not suggesting anyone should be using this. This was just my attempt on trying to solve this with the available template helpers and without any custom stuff.
Hope this helps

Lo primero es multiplicar por -1 para convertirlo en una valor negativo y guardarlo en una variable y posterior a usar la suma
The first thing is to multiply by -1 to turn it into a negative value
and save it in a variable and then use the add
{% widthratio val2 1 -1 as result %}
{{result|add:val1}}

After search I found that I can make {% with var=value %} with filters to make the arithmetic operations "with other variables or not"
For example: I have x = 5 and y = 3 and need to add the y's value to x value, all what I need is these steps:
1- Create variable x : {% with x=5 %}
2- Create variable y : {% with y=3 %}
3- In my HTML tags, say <h1>, write that : <h1>{{ x|add:y }}</h1>
4- Close the y's with : {% endwith %}
5- Close the x's with : {% endwith %}
Hope it works with you, it worked with me.
{% with i=3 %}
{% with x=1 %}
<h1>{{i|add:x}}</h1> <!-- result is 4 -->
{% endwith %}
{% endwith %}

django template print out by filter id value

I want to print value by id in database,And don't know which keywords to find in Google.
in my views.py, I send transen = TransEn.objects.all() to template
and this will print all datas from database:
{% for words in transen %}
{{words.words|safe }}
{% endfor %}
But I want to print by the value of the id Like:
(Because they are words in English for translating website)
I don't know how to write this in template, please guide me, Thank you very much.
<div><span> TransEn.objects.filter(id='2') </span></div>
<div> TransEn.objects.filter(id='3') </div>
UPDATE:
I have found a method:
I can use if tag, but are there another ideas??
<div>
{% for words in transen %}
{% if words.id == 2 %}
{{ words.words|safe }}
{% endif %}
{% endfor %}
</div>
<div>
{% for words in transen %}
{% if words.id == 3 %}
{{ words.words|safe }}
{% endif %}
{% endfor %}
</div>

If you want to access each item in the QuerySet individually, by index, you should cast it to a list first. You should change your views.py to:
transen = list(TransEn.objects.all())
And then in your template you can access them by index like so:
<div><span> {{ transen.1.words }} </span></div>
<div> {{ transen.2.words }} </div>
A warning from the Django docuemtnation about casting a QuerySet to a list:
Be warned, though, that this could have a large memory overhead, because Django will load each element of the list into memory. In contrast, iterating over a QuerySet will take advantage of your database to load data and instantiate objects only as you need them.

Does Jinja2 support nested if statements?

I read the docs and I am not clear on this is right at all. I know you can use nested for loops, but if statements seem to be different.
Can i do the following?
{% if thing=true %}
<div> something here</div>
{% if diffthing=true %}
<div> something else</div>
{% else %}
<div> third thing</div>
{% endif %}
{% else %}
<div> nothing here </div>
{% endif %}
Or should the format be different somehow?

Jinja2 supports nested blocks, including if statements and other control structures.
See the documentation on Block Nesting and Scope: "Blocks can be nested for more complex layouts."
A good use case for this is writing macros that conditionally output HTML:
{# A macro that generates a list of errors coming back from wtforms's validate function #}
{% macro form_error_summary(form, li_class='bg-danger') %}
{# only do the following on error... #}
{% if form.errors %}
<ul class="errors">
{# you can do layers of nesting as needed to render your content #}
{% for _field in form %}
{% if _field.errors %}
{% for error in _field.errors %}
<li class={{li_class}}>{{_field.label}}: {{ error|e }}</li>
{% endfor %}
{% endif %}
{% endfor %}
</ul>
{% endif %}
{% endmacro %}

The answer is yes.
I'm using logic very similar to yours in a live application and the nested if blocks work as expected. It can get a little confusing if you don't keep your code clean, but it works fine.

It seem possible. Refer to the documentation here: http://jinja.pocoo.org/docs/templates/#if

Just a quick add, if you're unpacking data to populate your fields, Jinja will only unpack it once. I had a similar problem with MongoDB and found if you change the item to a list item you iterate through it more than once without nesting
#app.route("/")
#app.route("/get_shrink")
def get_shrink():
# find and sort shrink top 5
shrink = list(mongo.db.shrinkDB.find().limit(5).sort(
"amount_lost_value", -1,))
return render_template(
"shrink.html", shrinkDB=shrink)
{% for shrink in shrinkDB %}
{% if shrink.resolved == true %}
<li>{{ shrink.product_name }} ||£ {{ shrink.amount_lost_value }} || {{ shrink.date }}</li>
{% endif %}
{% endfor %}
</span>
</div>
</div>
<div class="col s12 m5 offset-m2">
<h4>Top 5 Resolved Threats</h4>
<div class="card-panel light-blue">
<span class="white-text">
<!-- Shrink For loop top 5 resolves-->
{% for shrink in shrinkDB %}
{% if shrink.resolved != true %}
<li>{{ shrink.product_name }} ||£ {{shrink.amount_lost_value }} || {{ shrink.date }}</li>
{% endif %}
{% endfor %}

How can I use break and continue in Django templates?

I want to put break and continue in my code, but it doesn't work in Django template. How can I use continue and break using Django template for loop. Here is an example:
{% for i in i_range %}
{% for frequency in patient_meds.frequency %}
{% ifequal frequency i %}
<td class="nopad"><input type="checkbox" name="frequency-1" value="{{ i }}" checked/> {{ i }} AM</td>
{{ forloop.parentloop|continue }} ////// It doesn't work
{ continue } ////// It also doesn't work
{% endifequal %}
{% endfor%}
<td class="nopad"><input type="checkbox" name="frequency-1" value="{{ i }}"/> {{ i }} AM</td>
{% endfor %}

Django doesn't support it naturally.
You can implement forloop|continue and forloop|break with custom filters.
http://djangosnippets.org/snippets/2093/

For-loops in Django templates are different from plain Python for-loops, so continue and break will not work in them. See for yourself in the Django docs, there are no break or continue template tags. Given the overall position of Keep-It-Simple-Stupid in Django template syntax, you will probably have to find another way to accomplish what you need.

For most of cases there is no need for custom templatetags, it's easy:
continue:
{% for each in iterable %}
{% if conditions_for_continue %}
<!-- continue -->
{% else %}
... code ..
{% endif %}
{% endfor %}
break use the same idea, but with the wider scope:
{% set stop_loop="" %}
{% for each in iterable %}
{% if stop_loop %}{% else %}
... code ..
under some condition {% set stop_loop="true" %}
... code ..
{% endif %}
{% endfor %}
if you accept iterating more than needed.

If you want a continue/break after certain conditions, I use the following Simple Tag as follows with "Vanilla" Django 3.2.5:
#register.simple_tag
def define(val=None):
return val
Then you can use it as any variable in the template
{% define True as continue %}
{% for u in queryset %}
{% if continue %}
{% if u.status.description == 'Passed' %}
<td>Passed</td>
{% define False as continue %}
{% endif %}
{% endif %}
{% endfor %}
Extremely useful for any type of variable you want to re-use on template without using with statements.

In a Django template for loop, checking if current item different from previous item

I'm new to django and can't find a way to get this to work in django templates. The idea is to check if previous items first letter is equal with current ones, like so:
{% for item in items %}
{% ifequal item.name[0] previous_item.name[0] %}
{{ item.name[0] }}
{% endifequal %}
{{ item.name }}<br />
{% endforeach %}
Maybe i'm trying to do this in wrong way and somebody can point me in right direction.

Use the {% ifchanged %} tag.
{% for item in items %}
{% ifchanged item.name.0 %}
{{ item.name.0 }}
{% endifchanged %}
{% endfor %}
Also remember you have to always use dot syntax - brackets are not valid template syntax.