VPI Samples - lock_cpu() - AttributeError: 'vpi.Image' object has no attribute 'lock_cpu'

Hi,

I have Jetson AGX Xavier. I want to use vpi python library with python3.6.9 version. I run the sample application codes at the link bellow.
https://docs.nvidia.com/vpi/

Every sample code return the same error:

‘vpi.Image’ object has no attribute ‘lock_cpu’

Sample code:

import cv2

import sys

import vpi

import numpy as np

from argparse import ArgumentParser

 

# ----------------------------

# Parse command line arguments

 

parser = ArgumentParser()

parser.add_argument('backend', choices=['cpu','cuda','pva'],

                    help='Backend to be used for processing')

 

parser.add_argument('input',

                    help='Input image on which harris corners will be detected')

 

args = parser.parse_args();

 

if args.backend == 'cpu':

    backend = vpi.Backend.CPU

elif args.backend == 'cuda':

    backend = vpi.Backend.CUDA

else:

    assert args.backend == 'pva'

    backend = vpi.Backend.PVA

 

# --------------------------------------------------------------

# Load input into a vpi.Image and convert it to grayscale, signed 16bpp

with vpi.Backend.CUDA:

    input = vpi.asimage(cv2.imread(args.input), vpi.Format.BGR8).convert(vpi.Format.S16)

 

with backend:

    corners, scores = input.harriscorners(sensitivity=0.01)

 

# ---------------------------------------

# Render the keypoints in the output image

 

out = input.convert(vpi.Format.BGR8, backend=vpi.Backend.CUDA)

 

if corners.size > 0:

    with out.lock_cpu() as out_data, scores.lock_cpu() as scores_data, corners.lock_cpu() as corners_data:

        cmap = cv2.applyColorMap(np.arange(0, 256, dtype=np.uint8), cv2.COLORMAP_HOT)

 

        maxscore = scores_data.max()

 

        for i in range(corners.size):

            color = tuple([int(x) for x in cmap[255*scores_data[i]//maxscore,0]])

            kpt = tuple(corners_data[i].astype(np.int16))

            cv2.circle(out_data, kpt, 3, color, -1)

 

# -------------------

# Save result to disk

cv2.imwrite('harris_corners_python'+str(sys.version_info[0])+'_'+args.backend+'.png', out.cpu())

Thank you in advance…