code: def lookups(self, request, model_admin):
  		
  		statuses = [
  			[x, x.replace("_", " ").title()]
  			for x in models.Subscription.objects.values_list("status", flat=True).distinct()
  		]
  		statuses.append(["none", "No Subscription"])
  		return statuses
docs: Return a list of tuples.
  
  		The first element in each tuple is the coded value for the option that will
  		appear in the URL query. The second element is the
  		human-readable name for the option that will appear
  		in the right sidebar.
  		source: https://docs.djangoproject.com/en/1.10/ref/contrib/admin/#django.contrib.admin.ModelAdmin.list_filter