Context. I tried to subclass rdflib.URIRef and use it my code because I wanted to add additional functionality to it.

Expectations. I expected a subclass of URIRef to work exactly like URIRef itself works.

Reality. However, it appeared that SPARQL querying will not properly work in that case. Here is a full fledged example.

import rdflib
from rdflib import Graph, FOAF


class IRI(rdflib.URIRef):
    """Internationalized Resource Identifier."""

    def __repr__(self):
        """Format IRI."""
        return f'<{self.toPython()}>'


def test_uriref_subclass():
    graph = Graph()
    graph.add((
        IRI('https://example.com/Alice'),
        IRI(FOAF.knows),
        IRI('https://example.com/Bob'),
    ))

    bindings = graph.query(
        'SELECT * WHERE { ?s <http://xmlns.com/foaf/0.1/knows> ?o . }',
    ).bindings

    # Here we see that bindings are empty: nothing was found.
    assert not bindings

(This code should be runnable as-is.)

Since we added a triple to graph, I expected to find that triple via a SPARQL query but to no avail because FOAF.knows is saved as a IRI, not as a URIRef.

This is a non-standard pattern of usage, but would be great to see if anyone had circumvented such a problem.