<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_user(self, request):
 """ return active user or ``None`` """

        try:
            return User.objects.get(username=request.data.get('username'),
                                    is_active=True)
        except User.DoesNotExist:
            return None