How to bind parameters to SPARQL query without a local graph?

[Dan Davis]

I want to do binding on a SPARQL query before sending it over the wire.   Consider this query:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

PREFIX meshv: <http://id.nlm.nih.gov/mesh/vocab#>

SELECT ?descriptor ?label

FROM <http://id.nlm.nih.gov/mesh>

WHERE {

  ?descriptor a meshv:Descriptor .

  ?descriptor rdfs:label ?label .

  FILTER(REGEX(?label, 'Cobra'))

} 

ORDER BY ?label

How can I construct such a query without providing the expression literal, and then render it as a query?

I've gotten as far as this:

from rdflib.namespace import RDFS, Namespace

from rdflib.plugins.sparql import prepareQuery

MESHV = Namespace('http://id.nlm.nih.gov/mesh')

prefixen = { 'rdfs': RDFS, 'meshv': MESHV }

q = prepareQuery("""SELECT ?descriptor, ?label WHERE {

    ?descriptor a meshv:Descriptor .

    ?descriptor rdfs:label ?label .

    FILTER(REGEX(?label, ?expr)""", initNs=prefixen)

What do I do from here to bind the variable "expr" to the literal "Cobra" and then format back as a query?   What if I am attempting to construct or describe rather than select?  Looking at packages, rdfalchemy looks a lot better here than SPARQLWrapper, but rdfalchemy does not install in my Python 3 environment.

BTW - I'm the implementer and maintainer of the Medical Subject Headings (MeSH) in RDF, and the query I posit above can be run at https://id.nlm.nih.gov/mesh/query - enjoy.