Opencv 3 - python detectmultiscale; too many values to upack

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I'm trying to get access to either numDetections or rejectLevels and levelWeights so that I can judge confidence levels for each object detected by the cascade classifier. When I try:

faces, num_detections = faceCascade.detectMultiScale(
     gray,
     scale_factor = 3,
     minNeighbors = 3,
     minSize = (30, 30)
)

I get the error "too many values to unpack"

when I try

faces, reject_levesl, level_weights = faceCascade.detectMultiScale(
         gray,
         scale_factor = 3,
         minNeighbors = 3,
         minSize = (30, 30),
         outputRejectLevels = True
 )

I get the error outputRejectLevels is an invalid keyword argument for this function. Am I doing something horribly wrong? I'm running the current beta version of Opencv 3 and am on Arch linux. When I try and run the classifier normally it works like a charm. Any help greatly appreciated!