The following code is workable in the version 1.2:
#to convert opk into ypr
yaw, pitch, roll = PhotoScan.utils.mat2ypr(PhotoScan.utils.opk2mat(PhotoScan.Vector((omega, phi, kappa))).t())
#to convert ypr to opk
omega, phi, kappa = PhotoScan.utils.mat2opk(PhotoScan.utils.ypr2mat(PhotoScan.Vector((yaw, pitch, roll))).t())