Parametrized SPARQL Queries with python RDFLib

Question

I am trying to query a very simple database about Alloys with a parametrized SPARQL query using RDFLib:

x = "Inconel_625"

g = Graph()
g.parse ("Desktop/materials.ttl")


knows_query = """
SELECT ?min ?max
WHERE
{ ?s rdfs:label  """+x+""";
 mydb:min ?min ;
 mydb:max ?max.
}"""

qres = g.query(knows_query)
for x in qres:
    print(x.min, x.max)

Unfortunatly this code does not work. If i replace """+x+""" with "Inconel_625 it works somehow. What am i not seeing? Is it not possible to parametrize a sparql query in RDFLib?

Answer 1

Yes, rdflib supports parameterized queries by allowing one to bind values to variables via the initBindings keyword argument to Graph.query().

Here is your example code modified to use it:

from rdflib import Graph, Literal

label = "Inconel_625"

g = Graph()
g.parse("Desktop/materials.ttl")

knows_query = """
SELECT ?min ?max
WHERE
{ ?s rdfs:label ?label ;
 mydb:min ?min ;
 mydb:max ?max .
}"""

qres = g.query(knows_query, initBindings={"label": Literal(label)})
for x in qres:
    print(x.min, x.max)