Django; How To Organize Common Functions Or Similar Templates

I'm a beginner. I've been working on Django project. Now I'm trying to create notification part and I get the count of notifications.

The notification part is on like mypage. There are list menu on mypage and the part is common. Now I want to show up the count on the mypage but I'm wondering if I have to get common context.

there is a common part on pages that are belong to my page. inbox.html, my_profile.html etc.

<div class="list-group">
    <a target="_blank" rel="nofollow noreferrer" href="#">
        My page top
    </a>
    <a target="_blank" rel="nofollow noreferrer" href="#">
        Inbox
    <span class="badge badge-primary badge-pill">{{ this is the count of notifications }}</span>
    </a>

The function to get the count of notifications is like this

def get_number_of_notifications(self):
    notifications = Message.objects.filter(message_to=request.user, is_read=False).count()
    return notifications

and in views.py is like

def mypage_top(request):
   ...

def my_profile(request):
   ...

def inbox(request):
  ...

My question is basically do I have to write down the process to call the function on each view? I'm wondering if there's a better way.

Django views are only supposed to return the view-specific data as the template's context (for views using a template of course). To inject "common" data in your template's contexts, there are two main solutions: a context processor or a custom templatetag.

Context processors will be invoked for each and every template (well almost, cf the doc) so it's better to keep them for data that are "cheap" to get and are really useful for all views (typical examples are the auth and i18n processors).

For data that have an higher cost and may only be used in some of the templates you rather want a custom templatetag, and that's what I would use here. Don't be scared by the documentation, writing a custom templatetag like this one is really easy using an inclusion_tag.