When you use the extends template tag, you’re saying that the current template extends another — that it is a child template, dependent on a parent template. Django will look at your child template and use its content to populate the parent. Everything that you want to use in a child template should be within … Read more
Extending allows you to replace blocks (e.g. “content”) from a parent template instead of including parts to build the page (e.g. “header” and “footer”). This allows you to have a single template containing your complete layout and you only “insert” the content of the other template by replacing a block. If the user profile is … Read more
Besides putting my_templatetag.py inside app_name/templatetags, make sure you restart the Django development server (or ensure it restarted itself) every time you modify template tags. If the server does not restart, Django won’t register the tags.