You cannot use the range() function in the template. Rather do the following.
In your view.py add the following:

def index(request):
   files = listdir("/path/to/directory/")
   filelen = len(files)
   return render(request, 'path/to/template.html', {'filelen': filelen})

and then in your template loop using that range number as follows:

{%for i in filelen %}
 ...
{% endfor %}

So I am trying to get Django to display a template that shows a list of files on a local directory. My views.py looks like this:

from django.shortcuts import render
from django.http import HttpResponse
from os import listdir 
def index(request):
    files = listdir("/path/to/directory/")
    filelen = len(files)
    return render(request, 'path/to/template.html')

My html template looks like this:

{%for i in range(1, filelen)%}
<tr>
    <td>{{i}}</td>
    <td>{{files[i]}}</td>
    {% if "a" in files[i] %}
        <td>✓</td>
    {% else %}
        <td>x</td>
    {% endif %}
    {% if "b" in files[i] %}
        <td>✓</td>
    {% else %}
        <td>x</td>
{% endif %}

But when I try to run it I get the following error:

Error at line 39
'for' statements should use the format 'for x in y': for i in range(1, len_files)

Anybody know how to get this to work? I have tried replacing filelen with {{filelen}} but that gave me the same error.