Invalid filter error in django custom template filter

I'm trying to create a custom template filter but, getting Invalid filter error.

TemplateSyntaxError at /attainment/reportcard/
Invalid filter: 'get_item'
Request Method: POST
Request URL:    http://127.0.0.1:8000/attainment/reportcard/
Django Version: 1.11.5
Exception Type: TemplateSyntaxError
Exception Value:    
Invalid filter: 'get_item'
Exception Location: /media/itsd/ITSD/ROFI/Projects/Rise/venv/lib/python3.5/site-packages/django/template/base.py in find_filter, line 606
Python Executable:  /media/itsd/ITSD/ROFI/Projects/Rise/venv/bin/python
Python Version: 3.5.2

I've created a filter in template_filters.py and registered.

template_filters.py

from django.template.defaulttags import register

# Custom template filter to get data from a dictionary using key in template

@register.filter
def get_item(dictionary, key):
    return dictionary.get(key)

And I've used the filter in the template as follows.

<tbody>
    {% for subject in subjects %}
        <tr>
            <td>{{ subject|get_item:"subject" }}</td>
            <td>{{ subject|get_item:"efffort" }}</td>
            <td>{{ subject|get_item:"homework" }}</td>
            <td>{{ subject|get_item:"marks" }}</td>
            <td>{{ subject|get_item:"grade" }}</td>
        </tr>
    {% endfor %}
</tbody>

What am I missing ??

N.B: I've followed this answer.

You have to load the tag library before you use it in the template:

{% load template_filters %}

Or you can load the specific filter:

{% load get_item from template_filters %}

See the docs on custom template tags and the {% load %} tag for more info.