cannot import name 'region'

Hello, thanks for sharing your code. I encounted a problem when running 'demo.py'. I did all accoding to the Readme.
(siammask) bill@bill-QiTianM4550-N000:~/Documents/SiamMask/experiments/siammask$ python ../../tools/demo.py --resume SiamMask_DAVIS.pth --config config_davis.json
Traceback (most recent call last):
File "../../tools/demo.py", line 7, in
from tools.test import *
File "/home/bill/Documents/SiamMask/tools/test.py", line 30, in
from utils.pyvotkit.region import vot_overlap, vot_float2str
File "/home/bill/Documents/SiamMask/utils/pyvotkit/__init__.py", line 9, in
from . import region
ImportError: cannot import name 'region'
Then I deleted this project and reinstall it. However it shows again.