Python Rif Layer - 3

import prman
import sys

class myRif(prman.Rif):
    def __init__(self, ri, shadingrate):
        prman.Rif.__init__(self, ri)
        self.m_shadingrate = int(shadingrate)

    def ShadingRate(self, size):
        self.m_ri.ShadingRate(self.m_shadingrate)

if len(sys.argv) == 4:
    infile = sys.argv[1]
    outfile = sys.argv[2]
    shadingrate = sys.argv[3]
    prman.Init(["-catrib", outfile, "-progress"])
    ri = prman.Ri()
    rif1 = myRif(ri, shadingrate)
    prman.RifInit([rif1])
    ri.Option("rib", {"string asciistyle": "indented"})
    ri.Begin(ri.RENDER)
    prman.ParseFile(infile)
    ri.End()