more pep8 / pep257 cleaning of Graph.py
more pep8 / pep257 cleaning of Graph.py

dbs/rdflib,marma/rdflib,yingerj/rdflib,armandobs14/rdflib,armandobs14/rdflib,marma/rdflib,dbs/rdflib,yingerj/rdflib,avorio/rdflib,dbs/rdflib,marma/rdflib,RDFLib/rdflib,avorio/rdflib,RDFLib/rdflib,avorio/rdflib,RDFLib/rdflib,ssssam/rdflib,ssssam/rdflib,ssssam/rdflib,armandobs14/rdflib,yingerj/rdflib,dbs/rdflib,yingerj/rdflib,marma/rdflib,armandobs14/rdflib,RDFLib/rdflib,avorio/rdflib,ssssam/rdflib