I played with SPARQL on my local machine, and I also got inspired by Lee’s SPARQL library for Javascript. But, well, I prefer Python… So I made a set of utility classes first for myself, but then I decided to package it more properly. Maybe others can find it useful, too.
The goal is to give some help in turning a SPARQL query into the corresponding HTTP GET Protocol, send it to a SPARQL endpoint somewhere on the Web, and do something with the results. The simplest usage is something like:
from SPARQL import SPARQLWrapper
queryString = "SELECT * WHERE { ?s ?p ?o. }"
sparql = SPARQLWrapper("http://localhost:2020/sparql")
# add a default graph, though that can also be done in the query string
sparql.addDefaultGraph("http://www.example.com/data.rdf")
sparql.setQuery(queryString)
try :
ret = sparql.query() # ret is a stream with the results in XML, it is a file like object
except:
deal_with_the_exception() # eg, syntax error
To make it even easier to use, conversions to more Python-friendly formats can also done on the results: eg, turn it into a proper DOM tree if the result is XML, use Bob Ippolito’s simplejson module to convert a return format in JSON into Python dictionary, or parse it with RDFLib and return an RDFLib Graph in case the return is in RDF/XML. Ie, one could have done:
try :
sparql.setReturnFormat(SPARQL.JSON)
ret = sparql.query()
dict = ret.convert()
except:
deal_with_the_exception()
where “dict” is a Python dictionary. There are some more tricks in the library, but that essentially it…
The code is available from my site; the API documentation is included in the distribution (and is also available online).
It is an early release. There are some problems, and I expect some more. I have primarily tested it with two different SPARQL endpoints running on my local machine (joseki3 and virtuoso) and also with some public SPARQL endpoints. There are some differences on the return media type for, eg, JSON or N3, the non-standard arguments (eg, setting the return format) still diverge a bit, etc. But I would expect these to converge over time. However, I am sure that my code will have problems with some of the endpoints at least on those grounds (or others)…
