Why transpose rotation matrix when load K, R and t from P?

[klyjm]

In the function load_K_Rt_from_P(), the rotation matrix was transposed after got from the cv2.decomposeProjectionmatrix(). As I know, the result from the cv2.decomposeProjectionmatrix() is the really rotation matrix and t and not need to be changed, why the rotation matrix iwas transposed but others was not changed.