I am newbie in Python and I am trying to price a CDS Option in quantlib Python. I have the below code:

    expiry= ql.Date(15,ql.May,2012)
    cds_vol=0.5
    exercise = ql.EuropeanExercise(expiry)
    cds_option=ql.CdsOption(cds, exercise, True)
    risk_free_rate = ql.YieldTermStructureHandle(ql.FlatForward(todaysDate, 0.01, ql.Actual365Fixed()))
    probability = ql.DefaultProbabilityTermStructureHandle(hazard_curve)
    cds = ql.CreditDefaultSwap(ql.Protection.Seller, nominal, s, schedule, ql.Following, ql.Actual365Fixed())
    engine = ql.MidPointCdsEngine(probability, recovery_rate, risk_free_rate)
    cds.setPricingEngine(engine)
    cds_option_price=cds_option.setPricingEngine((ql.BlackCdsOptionEngine(probability, recovery_rate, risk_free_rate,cds_vol)))
    cds_option_price.NPV()



This gives me an error:TypeError: in method 'new_BlackCdsOptionEngine', argument 4 of type 'Handle< Quote > const &'