filter_for_past_30_days.py

# Import datetime
from datetime import date, timedelta

# date.today() returns the current date
# timedelta(days=X) takes the "days" attribute to subtract days from the current date
date = date.today() - timedelta(days=30)

# The "__gte" lookup search finds records where the date
# is greater than or equal to the comparison value
object_list = Model.objects.filter(date_at__gte=date)

Corretíssimo, Vinícius! Falta de atenção no uso do lookup. Corrigido!