OpenCV (Python) unpack SIFT Octave

Question

I just discovered that SIFT writes the Octave as packed value (octave, layer and scale).
I need this value unpacked since I have to use SIFT detector in combination with other descriptors (ORB, BRIEF, SURF, BRISK). Here you can find a similar question.
I already tried different solutions (see code below) but none seems to work in python (this one as well).
Any suggestion?

unpackOctave(keypoints[i], octave, layer, scale)     

or:

unpackOctave(const KeyPoint& kpt, int& octave, int& layer, float& scale){    
    octave = kpt.octave & 255;    
    layer = (kpt.octave >> 8) & 255;    
    octave = octave < 128 ? octave : (-128 | octave);    
    scale = octave >= 0 ? 1.f/(1 << octave) : (float)(1 << -octave);    
}

Answer 1

I define a Python function to unpack SIFT Octave:

#!/usr/bin/python3
## 2018.01.23 11:12:30 CST
## created by Silencer

def unpackSIFTOctave(kpt):
    """unpackSIFTOctave(kpt)->(octave,layer,scale)
    @created by Silencer at 2018.01.23 11:12:30 CST
    @brief Unpack Sift Keypoint by Silencer
    @param kpt: cv2.KeyPoint (of SIFT)
    """
    _octave = kpt.octave
    octave = _octave&0xFF
    layer  = (_octave>>8)&0xFF
    if octave>=128:
        octave |= -128
    if octave>=0:
        scale = float(1/(1<<octave))
    else:
        scale = float(1<<-octave)
    return (octave, layer, scale)

---

For example, I detect the sift kpts on the panda.

Use unpackSiftOctave to unpack the sift kpts, get a list of (octave, layer, scale). Part of the unpacked result.

[(0, 3, 1.0),
 (1, 3, 0.5),
 (-1, 3, 2.0),
 (-1, 3, 2.0),
 (2, 1, 0.25),
 (2, 1, 0.25),
 (-1, 1, 2.0),
 (-1, 1, 2.0),
 (0, 2, 1.0),
 (1, 3, 0.5),
 ...
]