如何检索由 rdflib 加载的本体的命名空间

Question

I created an ontology and now I want to read it using rdflib. the question is how to get the URI (namespace) or the prefix of the loaded graph with out manually inspecting the ontology as below:

from rdflib import *

rdf_address="C:/Users/eh/ontologies/RNO_V5042/NVDB_RNO_V5042_RDF.owl"
g=Graph()
g.parse(rdf_address)

for namespace in g.namespaces():
    print namespace

rno = Namespace("http://www.semanticweb.org/eh/ontologies/2015/3/RNO_V5042#") ###### **how to find this namespace?**

aClass = rno.Node
roundabout= rno.Roundabout
namedIndividual = URIRef('http://www.w3.org/2002/07/owl#NamedIndividual')
rdftype = URIRef("http://www.w3.org/1999/02/22-rdf-syntax-ns#type")
for triple in g.triples((None,rdftype,rno.Roundabout)):
    print triple

Answer 1

Having a rdflib Graph, parse() it and use MyNameSpace(g). This gives the namespace for empty prefix, ie, ":".

from rdflib import Graph

g = Graph() 
cOntoFile = "MyOnto.ttl"
g.parse(cOntoFile, format="turtle")

print(MyNameSpace(g))

def MyNameSpace(g):
  for ns_prefix, namespace in g.namespaces():
    if not ns_prefix:
      return namespace
  return ""