dist = lineStr.project(refPt)

np = lineStr.interpolate(dist) # using shapely

SELECT AsText(ClosestPoint(GeomFromText('LINESTRING(0 0, 0 4)') , GeomFromText('POINT(2 2)') ))

POINT(0 2)

from pyspatialite import dbapi2
conn = dbapi2.connect('path_to_your_database/db.sqlite')
cur = conn.cursor()
qry = "SELECT AsText(ClosestPoint(GeomFromText('LINESTRING(0 0, 0 4)'), GeomFromText('POINT(2 2)') ))"
cur.execute(qry)
cur.fetchone()[0]