I was fairly confused about this for some time but I finally learned how to parse a large N-Triples RDF store (.nt) using Raptor and the Redland Python Extensions.
A common example is to do the following:
import RDF
parser=RDF.Parser(name="ntriples")
model=RDF.Model()
stream=parser.parse_into_model(model,"file:./mybigfile.nt")
for triple in model:
print triple.subject, triple.predicate, triple.object
Parse_into_model() by default loads the object into memory, so if you are parsing a big file you could consider using a HashStorage as your model and serializing it that way.
But what if you want to just read the file and say, add it to MongoDB without loading it into a Model or anything complicated like that?