About: http://webisa.webdatacommons.org/247270630

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	By default, get() returns the empty string ('') So your code is correct, but instead of checking whether a or b are None, you should check for empty strings.
http://www.w3.org/ns/prov#wasQuotedFrom	stackoverflow.com