How do I filter objects in datetime fields?

I have the following model:

class Announcement(models.Model):
    name = models.CharField(max_length=500)
    content = models.CharField(max_length=1000)
    is_active = models.BooleanField(default=False)
    date_start = models.DateTimeField()
    date_end = models.DateTimeField()

    def __str__(self):
        return self.name

      

        
        
        
      

    

I can filter objects in a field is_active

, for example:

def announcements(request):
    announcements = Announcement.objects.all().filter(
        is_active = True
    )
    return HttpResponse(
        serializers.serialize("json", announcements))

      

        
        
        
      

    

This works great. But when I want to filter them based on the field date_start

like this:

def announcements(request):
    announcements = Announcement.objects.all().filter(
        date_start >= datetime.now()
    )
    return HttpResponse(
        serializers.serialize("json", announcements))

      

        
        
        
      

    

I am getting error global name 'date_start' is not defined

.