import rdflib
from rdflib import Graph, URIRef, Literal, Namespace

SH = Namespace("http://bug/")

graph = Graph()
graph.bind('sh',SH)
graph.add((SH.a,SH.p,SH.b))
graph.add((SH.b,SH.p,SH.c))
graph.add((SH.x,SH.p,SH.y))

# finding a chain of length three
q1 = """SELECT ?here ?there ?elsewhere
WHERE { ?here  sh:p ?there .
        ?there sh:p ?elsewhere . }"""
r1 = graph.query(q1)
for row in r1 : r1r = row; print row

# also should find *and report* the chain, but doesn't report correctly
q2 = """SELECT ?here ?there ?elsewhere
WHERE { ?here  sh:p ?there .
        { SELECT ?there ?elsewhere WHERE { ?there sh:p ?elsewhere . } } }"""
r2 = graph.query(q2)
for row in r2: r2r = row; print row

# also should find *and report* the chain, and does
q3 = """SELECT ?here ?there ?elsewhere
WHERE { { SELECT ?there ?elsewhere WHERE { ?there sh:p ?elsewhere . } } 
	?here  sh:p ?there . }"""
r3 = graph.query(q3)
for row in r3: r3r = row; print row

assert r1r[0] == r2r[0]
assert r1r[1] == r2r[1]
assert r1r[2] == r2r[2]

assert r3r[0] == r2r[0]
assert r3r[1] == r2r[1]
assert r3r[2] == r2r[2]