<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def active(self):
 """Returns all outlets that are currently active and have sales."""

        qs = self.get_queryset()
        return qs.filter(
            models.Q(
                models.Q(start_date__isnull=True) |
                models.Q(start_date__lte=now().date())
            ) &
            models.Q(
                models.Q(end_date__isnull=True) |
                models.Q(end_date__gte=now().date())
            )
        ).distinct()