python - Django objects queryset filter by matching datetime -

i have model field name 'timestamp' datetime field, , when print them in python manage.py shell get:

>>> a.timestamp datetime.datetime(2013, 7, 15, 18, 45, tzinfo=<utc>) 

now.... running django celery task every 30 seconds suppose retrieve matching objects in last 30 seconds.

how can (thing = mymodelname.objects.filter(.. ..)

i hope manage explain self.

thank in advanced.

update: when typing in server (python shell)

datetime.datetime.now() getting

datetime.datetime(2013, 7, 15, 20, 34, 4, 366166)

mymodelname.objects.filter(timestamp__gte=(datetime.datetime.now() - datetime.timedelta(seconds=30)))