At Django Tables2 documentation:
http://django-tables2.readthedocs.org/en/latest/#subclassing-column
Example of this section is ImageColumn.
For complicated columns, you may want to return HTML from the render() method. This is fine, but be sure to mark the string as safe to avoid it being escaped:
>>> from django.utils.safestring import mark_safe
>>> from django.utils.html import escape
>>>
>>> class ImageColumn(tables.Column):
... def render(self, value):
... return mark_safe('<img src="/media/img/%s.jpg" />'
... % escape(value))
...
Link to official documentation: https://github.com/bradleyayers/django-tables2/blob/master/docs/index.rst (just in case)