How to export graph in RDF file using RDFLib

Question

I'm trying to generate RDF data using RDFLib in Python 3.4.

A minimal example:

from rdflib import Namespace, URIRef, Graph
from rdflib.namespace import RDF, FOAF

data = Namespace("http://www.example.org#")

g = Graph()

g.add( (URIRef(data.Alice), RDF.type , FOAF.person) )
g.add( (URIRef(data.Bob), RDF.type , FOAF.person) )
g.add( (URIRef(data.Alice), FOAF.knows, URIRef(data.Bob)) )

#write attempt
file = open("output.txt", mode="w")
file.write(g.serialize(format='turtle'))

This code results in the following error:

file.write(g.serialize(format='turtle'))
TypeError : must be str, not bytes

If I replace the last line with:

file.write(str(g.serialize(format='turtle')))

I do not get the error, but the result is a string representation of a binary stream (a single line of text starting with b'):

b'@prefix ns1: <http://xmlns.com/foaf/0.1/> .\n@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .\n@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .\n@prefix xml: <http://www.w3.org/XML/1998/namespace> .\n@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .\n\n<http://www.example.org#Alice> a ns1:person ;\n    ns1:knows <http://www.example.org#Bob> .\n\n<http://www.example.org#Bob> a ns1:person .\n\n'

Question How do I correctly export the graph into a file?

Answer 1

The serialize method accepts a destination keyword that is a file path. In your example, you would want to use:

g.serialize(destination='output.txt', format='turtle')

Instead of

file = open("output.txt", "w")
file.write(g.serialize(format='turtle'))