You can use the [`add`](https://docs.djangoproject.com/en/dev/ref/templates/builtins/#add) filter:

    {{ object.article.rating_score|add:&quot;-100&quot; }}

Use [django-mathfilters][1]. In addition to the built-in add filter, it provides filters to subtract, multiply, divide, and take the absolute value.

For the specific example above, you would use `{{ 100|sub:object.article.rating_score }}`.


  [1]: http://pypi.python.org/pypi/django-mathfilters

Generally it is recommended you do this calculation in your view. Otherwise, you could use the add filter.

I&#39;m trying to sort an array of numbers that are strings and I&#39;d like them to sort numerically.

The catch is that **I cannot convert the numbers into int**.

Here is the code:

    string[] things= new string[] { &quot;105&quot;, &quot;101&quot;, &quot;102&quot;, &quot;103&quot;, &quot;90&quot; };
    
    foreach (var thing in things.OrderBy(x =&gt; x))
    {
    	Console.WriteLine(thing);
    }


*Output*:
``` 
101, 102, 103, 105, 90
```

I&#39;d like: 
```
90, 101, 102, 103, 105
```

**EDIT:**
The output can&#39;t be `090, 101, 102...` 

Updated the code sample to say &quot;`things`&quot; instead of &quot;`sizes`&quot;. The array can be something like this:  

    string[] things= new string[] { &quot;paul&quot;, &quot;bob&quot;, &quot;lauren&quot;, &quot;007&quot;, &quot;90&quot; };

That means it needs to be sorted alphabetically and by number:
```
007, 90, bob, lauren, paul
```

How do I sort strings alphabetically while accounting for value when a string is numeric?

    class obj
    {
        int typeId; //10 types  0-9 
        string uniqueString; //this is unique
    }

Assume there is a list with 100 elements of objs, but only 10 unique typeIDs.

Is it possible to write a LINQ query that returns the 10 unique ints from the list of objs?



LINQ query to return distinct field values from list of objects

I want to do this:

    100 - {{ object.article.rating_score }} 

So for example, the output would be `20` if `{{ object.article.rating_score }}` equaled `80`.

How do I do this at the template level? I don&#39;t have access to the Python code.

How to do math in a Django template?

I want to do this:
<pre><code class="hljs language-csharp">100 - {{ object.article.rating_score }} 
</code></pre>
So for example, the output would be <code>20</code> if <code>{{ object.article.rating_score }}</code> equaled <code>80</code>.
How do I do this at the template level? I don't have access to the Python code.

I want to get all the `&lt;a&gt;` tags which are children of `&lt;li&gt;`:

&lt;!-- language: lang-html --&gt;

    &lt;div&gt;
    &lt;li class=&quot;test&quot;&gt;
        &lt;a&gt;link1&lt;/a&gt;
        &lt;ul&gt; 
           &lt;li&gt;  
              &lt;a&gt;link2&lt;/a&gt; 
           &lt;/li&gt;
        &lt;/ul&gt;
    &lt;/li&gt;
    &lt;/div&gt;


I know how to find element with particular class like this:


    soup.find(&quot;li&quot;, { &quot;class&quot; : &quot;test&quot; }) 

But I don&#39;t know how to find all `&lt;a&gt;` which are children of `&lt;li class=test&gt;` but not any others.

Like I want to select:

&lt;!-- language: lang-html --&gt;

    &lt;a&gt;link1&lt;/a&gt;



How to find children of nodes using BeautifulSoup

Why am I getting this error, from line 5 of my code, when attempting to solve Project Euler Problem 11?

```lang-python
for x in matrix:
	p = 0
	for y in x:
		if p &lt; 17:
			currentProduct = int(y) * int(x[p + 1]) * int(x[p + 2]) * int(x[p + 3])
			if currentProduct &gt; highestProduct:
				print(currentProduct)
				highestProduct = currentProduct
		else:
		        break
			p += 1
```

```lang-none
&#39;generator&#39; object is not subscriptable
```


&quot;&#39;generator&#39; object is not subscriptable&quot; error

How would I add a user to a group in django by the group&#39;s name?

I can do this:

    user.groups.add(1) # add by id

How would I do something like this:

    user.groups.add(name=&#39;groupname&#39;) # add by name

Adding a user to a group in django

Consider:

    $ cat bla.py 
    u = unicode(&#39;d…&#39;)
    s = u.encode(&#39;utf-8&#39;)
    print s
    $ python bla.py 
      File &quot;bla.py&quot;, line 1
    SyntaxError: Non-ASCII character &#39;\xe2&#39; in file bla.py on line 1, but no encoding declared; see http://www.python.org/peps/pep-0263.html for details

How can I declare UTF-8 strings in source code?


Working with UTF-8 encoding in Python source

Can a Python function be an argument of another function?

Say:

    def myfunc(anotherfunc, extraArgs):
        # run anotherfunc and also pass the values from extraArgs to it
        pass

So this is basically two questions:

1. Is it allowed at all?
2. And if it is, how do I use the function inside the other function? Would I need to use exec(), eval() or something like that? Never needed to mess with them.

BTW, extraArgs is a list/tuple of anotherfunc&#39;s arguments.


Python function as a function argument?

I&#39;m starting to organize a new project and let&#39;s say i&#39;ll have a few models like **products** and **catalogs**.

I will allow my clients (not visitors, only specific clients) to login on Django Admin site to create, edit and delete their own catalogs.

Lets say I create a model called **&quot;Shop&quot;**, create every shop (name, address, logo, contact info and etc.) and create an admin user binded to that shop.

Now I want this new admin (who&#39;s not a site admin, but a shop admin -- probably an **user group**) to see and edit **only the catalogs linked with his shop**.

Is that possible?

Should I do this inside the Django Admin or should I create a new &quot;shop admin&quot; app?

Django Admin - Specific user (admin) content

Django

I have next models:

    class Group(models.Model):
        name = models.CharField(max_length=100)
        parent_group = models.ManyToManyField(&quot;self&quot;, blank=True)
        
        def __unicode__(self):
            return self.name
    
    
    class Block(models.Model):
        
        name = models.CharField(max_length=100)
        app = models.CharField(max_length=100)
        group = models.ForeignKey(Group)
    
        def __unicode__(self):
            return self.name


say, block **b1** has **g1** group. By it&#39;s name I want to get **all blocks** from group **g1**. I wrote next recursive function:


    def get_blocks(group):
        
        def get_needed_blocks(group):
            for block in group.block_set:
                blocks.append(block)
    
            if group.parent_group is not None:
                get_needed_blocks(group.parent_group)
    
        blocks = []
        get_needed_blocks(group)
        return blocks
        
but **b1.group.block_set** returns me **RelatedManager** object, which is not iterable.

What to do? What&#39;s wrong?

TypeError: &#39;RelatedManager&#39; object is not iterable

How would I delete an object from a Many-to-Many relationship without removing the actual object?

**Example:**

I have the models `Moods` and `Interest`.

`Mood` has a many-to-many field `interests` (which is a `models.ManyToManyField(Interest)`). 

I create an instance of `Moods` called `my_mood`. In `my_moods`&#39;s interests field I have `my_interest`, meaning 

    &gt;&gt;&gt; my_mood.interests.all()
    [my_interest, ...]

How do I remove `my_interest` from `my_mood` without deleting either model instance? In other words, how do I remove the relationship without affecting the related models?

Django removing object from ManyToMany relationship

I have this model I&#39;m showing in the admin page:

    class Dog(models.Model):
        bark_volume = models.DecimalField(...
        unladen_speed = models.DecimalField(...
    
        def clean(self):
            if self.bark_volume &lt; 5:
                raise ValidationError(&quot;must be louder!&quot;)

As you can see I put a validation on the model.  But what I want to happen is for the admin page to show the error next to the bark_volume field instead of a general error like it is now.  Is there a way to specify which field the validation is failing on?

Much thanks in advance.


Django - How to specify which field a validation fails on?

I have _users_, _videos_, _topics_, _criterias_ and _ratings_

- A _video_ has a _topic_
- A _topic_ has _criterias_
- A _user_ can create a _video_ for a given _topic_
- A _user_ can rate a _video_ on each _criterias_ given for the concerned _topic_.

You can see my original post https://stackoverflow.com/questions/6388259/django-rating-model-example-detailview-template to get details on the model used

I have extended a `DetailView` template based on the _video_ model to put the list of _ratings_ for the selected _video_ for a given _user_ as extra context.

    class VideoFileDetailView(DetailView):
      model = VideoFile

      def get_context_data(self, **kwargs):
        context = super(VideoFileDetailView, self).get_context_data(**kwargs)
        context[&#39;rates&#39;] = VideoRate.objects.filter(video=self.object, user=self.request.user)
        return context

In the template pointed by the `DetailView`, I&#39;d like to list the _criterias_ of the _video_, and for each _criteria_ display the current **rating value** form the _user_.


    &lt;div id=&quot;rating&quot;&gt;
      &lt;ul&gt;
    {% for crit in videofile.topic.crits.all %}
        &lt;li&gt;
      {% for rate in rates %}
        {% if rate.crit.id == crit.id %}
          {{ rate.rate }}
        {% endif %}
      {% endfor %}
          &lt;div class=&quot;rateit&quot;
            data-rateit-value=&quot;{# The rating value #}&quot;
            data-rateit-ispreset=&quot;true&quot;
            crit-id=&quot;{{ crit.id }}&quot;&gt;&lt;/div&gt;
          {{ crit }}
        &lt;/li&gt;
    {% endfor %}
      &lt;/ul&gt;
    &lt;/div&gt;

([rateit][1] is a jquery plugin that I use to draw pretty stars rating controls)

Actually I get my rating values here within the 2nd `for` but I&#39;m sure there is a better way to do that. In fact, I&#39;m still not sure about my [model][2] correctness.

Finally I&#39;d like to replace `{# The rating value #}` by the rating value from rate for the current crit (in the loop). How can I do that ?

  [1]: http://www.radioactivethinking.com/rateit/example/example.htm
  [2]: https://stackoverflow.com/questions/6388259/django-rating-model-example-detailview-template

Django - Simple custom template tag example

Is it possible to sort a set of related items in a DJango template?

That is: this code (with HTML tags omitted for clarity):

    {% for event in eventsCollection %}
       {{ event.location }}
       {% for attendee in event.attendee_set.all %}
         {{ attendee.first_name }} {{ attendee.last_name }}
       {% endfor %}
     {% endfor %}

displays ***almost*** exactly want I want.  The only thing I want to change is I the list of attendees to be sorted by last name.  I&#39;ve tried saying something like this:

    {% for event in events %}
       {{ event.location }}
       {% for attendee in event.attendee_set.order_by__last_name %}
         {{ attendee.first_name }} {{ attendee.last_name }}
       {% endfor %}
     {% endfor %}

Alas, the above syntax doesn&#39;t work (it produces an empty list) and neither does any other variation I have thought of (lot&#39;s of syntax errors reported, but no joy).   

I could, of course, produce some kind of array of sorted attendee lists in my view, but that is an ugly and fragile (and did I mention ugly) solution.

Needless to say, but I&#39;ll say it anyway, I have perused the on-line docs and searched Stack Overflow and the archives of django-user without finding anything helpful (ah, if only a query set were a dictionary dictsort would do the job, but it&#39;s not and it doesn&#39;t)

==============================================

Edited to add additional thoughts
after accepting Tawmas&#39;s answer.

-----------------------------------------------
Tawmas addressed the issue exactly as I presented it -- although the solution was not what I expected.  As a result I learned a useful technique that can be used in other situations as well. 

Tom&#39;s answer proposed an approach I had already mentioned in my OP and tentatively rejected as being &quot;ugly&quot;.  

The &quot;ugly&quot; was a gut reaction, and I wanted to clarify what was wrong with it.  In doing so I realized that the reason it was an ugly approach was because I was hung up on the idea of passing a query set to the template to be rendered.   If I relax that requirement, there is an un-ugly approach that should work.  

I haven&#39;t tried this yet, but suppose that rather than passing the queryset, the view code iterated through the query set producing a list of Events, then decorated each Event with a query set for the corresponding attendees which _WAS_ sorted (or filtered, or whatever) in the desired way.   Something like so:
 
    eventCollection = []   
    events = Event.object.[filtered and sorted to taste]
    for event in events:
       event.attendee_list = event.attendee_set.[filtered and sorted to taste]
       eventCollection.append(event)

Now the template becomes:

    {% for event in events %}
       {{ event.location }}
       {% for attendee in event.attendee_list %}
         {{ attendee.first_name }} {{ attendee.last_name }}
       {% endfor %}
     {% endfor %}


The downside is the view has to &quot;actualize&quot; all of the events at once which could be a problem if there were large numbers of events.  Of course one could add pagination, but that complicates the view considerably.  

The upside is the &quot;prepare the data to be displayed&quot; code is in the view where it belongs letting the template focus on formatting the data provided by the view for display. This is right and proper.
       
So my plan is to use Tawmas&#39; technique for large tables and the above technique for small
tables, with the definition of large and small left to the reader (grin.)
        


Sorting related items in a Django template

I have this code

    {% for o in some_list %}

Now I want to do some stuff if I am on an even line. How can I do that?

How do I get odd and even values in a Django for loop template?

I&#39;ve checked out tons of tutorials for django AJAX forms, but each one of them tells you one way of doing it, none of them is simple and I&#39;m a bit confused since I&#39;ve never worked with AJAX.

I have a model called &quot;note&quot;, a modelform for it, and inside the template I need that everytime a note element sends the stop() signal (from jQuery Sortables) django updates the object.

My current code:

**views.py**

    def save_note(request, space_name):
    
        &quot;&quot;&quot;
        Saves the note content and position within the table.
        &quot;&quot;&quot;
        place = get_object_or_404(Space, url=space_name)
        note_form = NoteForm(request.POST or None)
            
        if request.method == &quot;POST&quot; and request.is_ajax:
            msg = &quot;The operation has been received correctly.&quot;          
            print request.POST
    
        else:
            msg = &quot;GET petitions are not allowed for this view.&quot;
            
        return HttpResponse(msg)

**JavaScript:**

    function saveNote(noteObj) {
        /*
            saveNote(noteObj) - Saves the notes making an AJAX call to django. This
            function is meant to be used with a Sortable &#39;stop&#39; event.
            Arguments: noteObj, note object.
        */
        var noteID = noteObj.attr(&#39;id&#39;);
        
        $.post(&quot;../save_note/&quot;, {
            noteid: noteID,
            phase: &quot;Example phase&quot;,
            parent: $(&#39;#&#39; + noteID).parent(&#39;td&#39;).attr(&#39;id&#39;),
            title: $(&#39;#&#39; + noteID + &#39; textarea&#39;).val(),
            message: &quot;Blablbla&quot;,
        });
    }

The current code gets the data from the template and prints it in the terminal. I don&#39;t know how I can manipulate this data. I&#39;ve seen some people manages the data through jqueryforms to send the data to django.

How can I access the data sent by AJAX and update the note object?

How to POST a django form with AJAX &amp; jQuery

In Django templates, you can use either `{{ _(&quot;Hello World&quot;) }}` or `{% trans &quot;Hello World&quot; %}` to mark strings to be translated. In docs, the “official” approach seems to be the [`{% trans %}`](https://docs.djangoproject.com/en/1.8/topics/i18n/translation/#trans-template-tag) tag, but the `_()` syntax is mentioned too [once](https://docs.djangoproject.com/en/1.8/topics/i18n/translation/#string-literals-passed-to-tags-and-filters).

**How these approaches differ** (except syntax) and why should be one preferable rather than the other?

One difference is that you obviously can&#39;t use `{% trans %}` with tags and filters. But does that mean that I can just use `_()` everywhere, like `{{ _(&quot;String&quot;) }}`? It works and looks much cleaner and more consistent than using `{% trans &quot;String&quot; %}` with standalone strings and `_()` with tags and filters.

Content Type	Original Author	Original Content on Stackoverflow
Question	Tommy	View Question on Stackoverflow
Solution 1 - Python	Daniel Roseman	View Answer on Stackoverflow
Solution 2 - Python	Erik	View Answer on Stackoverflow
Solution 3 - Python	bdd	View Answer on Stackoverflow

How to do math in a Django template?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

LINQ query to return distinct field values from list of objects

How do I sort strings alphabetically while accounting for value when a string is numeric?

Attributions