django template question (accessing a list)

python django django-templates

12,978

Solution 1

You use the dot-operator to index the array, or, really, to do anything.

Technically, when the template system encounters a dot, it tries the following lookups, in this order:
* Dictionary lookup
* Attribute lookup
* Method call
* List-index lookup

I don't believe you can do math on the index. You'll have to pass in your array constructed in some other way so that you don't have to do this subtraction.

Solution 2

In short, Django doesn't do what you want.

The for loop has a number of useful properties within a loop.

forloop.counter     The current iteration of the loop (1-indexed)
forloop.counter0    The current iteration of the loop (0-indexed)
forloop.revcounter  The number of iterations from the end of the loop (1-indexed)
forloop.revcounter0 The number of iterations from the end of the loop (0-indexed)
forloop.first       True if this is the first time through the loop
forloop.last        True if this is the last time through the loop
forloop.parentloop  For nested loops, this is the loop "above" the current one

You could probably use forloop.counter0 to get the zero-based indexes you want; unfortunately, the Django template language doesn't support variable array indexes (You can do {{ foo.5 }}, but you can't do {{ foo.{{bar}} }}).

What I usually do is to try and arrange the data in the view to make it easier to present in the template. As an example, for you could create an array in your view composed of dictionaries so that all you have to do is loop through the array and pull exactly what you need out of the individual dictionaries. For really complicated things, I've gone so far as to create a DataRow object that would correctly format the data for a particular row in a table.

Solution 3

Try using "slice" to access a list by index

http://docs.djangoproject.com/en/dev/ref/templates/builtins/#slice

12,978

Author by

skyeagle

Updated on June 25, 2022

Comments

skyeagle almost 2 years
I am writing a template for my first django website.

I am passing a list of dictionaries to the template in a variable. I also need to pass a few other lists which hold boolean flags. (Note: all lists have the same length)

The template looks something like this:
```
<html>
    <head><title>First page</title></head><body>
        {% for item in data_tables %}
        <table>
        <tbody>
                  <tr><td colspan="15">
                  {% if level_one_flags[forloop.counter-1] %}
                  <tr><td>Premier League
                  {% endif %}
                  <tr><td>Junior league
                  <tr><td>Member count
                  {% if level_two_flags[forloop.counter-1] %}
                  <tr><td>Ashtano League
                  {% endif %}
             </tbody>
        </table>
        {% endfor %}
  </body>
</html>
```
I am getting the following error:

Template error

In template /mytemplate.html, error at line 7 Could not parse the remainder: '[forloop.counter-1]' from 'level_one_flags[forloop.counter-1]'

I am, not suprised I am getting this error, since I was just trying to see if would work. So far, from the documentation, I have not found out how to obtain the items in a list by index (i.e. other than by enumeration).

Does anyone know how I may access a list by index in a template?