pip3 install opencv-python fails on 'skbuild'

[snippsat]

pedro@pedro-512ssd:~$ pip3 install --upgrade pip3
Collecting pip3

this fails.

It is like this no pip3 last when upgrade,test with pip3 -V after.

pip3 install --upgrade pip
# Or if need sudo
sudo pip3 install --upgrade pip

# Then install
pip3 install opencv-python
# Or no sudo
pip3 install --user opencv-python

To get upgrade of all look at pyenv Simple Python Version Management
A 2-minutte demo to install Python 3.8.5 and opencv-python.

# install 3.8.5
mint@mint ~ $ pyenv install 3.8.5
Installing Python-3.8.5...
Installed Python-3.8.5 to /home/mint/.pyenv/versions/3.8.5
 
# Set global(system wide)
mint@mint ~ $ pyenv global 3.8.5

# Test pip
tom@tom-VirtualBox:~$ pip -V
pip 20.2.3 from /home/tom/.pyenv/versions/3.8.5/lib/python3.8/site-packages/pip (python 3.8)

# Install opencv-python
tom@tom-VirtualBox:~$ pip install opencv-python
Collecting opencv-python ...
Successfully installed opencv-python-4.4.0.42

# Test that it work
tom@tom-VirtualBox:~$ python
Python 3.8.5 (default, Sep 15 2020, 12:43:19) 
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2

>>> 
>>> cv2.__version__
'4.4.0'
>>> exit()