from rdflib import Graph, Namespace, Literal

# Define some namespaces

rdf = Namespace("http://www.w3.org/1999/02/22-rdf-syntax-ns#");
dc = Namespace("http://purl.org/dc/elements/1.1/")
census = Namespace("tag:govshare.info,2005:rdf/census/")
usgovt = Namespace("tag:govshare.info,2005:rdf/usgovt/");

# Create a store to hold RDF data

store = Graph();

# Load the N3 file with the states data

store.parse("states.n3", None, 'n3');

# Loop through every statement in the graph of the form
# ( ____ rdf:type usgovt:State).

totalpop = 0
statecount = 0

for statement in store.triples((None, rdf["type"], usgovt["State"])):
	state = statement[0] # the subject of the statement
	population = store.value(state, census["population"], None)
	population = int(population) # convert from Literal to integer
	totalpop = totalpop + population
	statecount = statecount + 1

print totalpop/statecount