I finally managed to use Python correctly from Macports I first deleted the installation performed by the installer of python.org :
- /Library/Frameworks/Python.framework (Thanks Chris Jones and Ryan Schmidt for the reference to the Macports FAQ) - /Application/Python 3.8 - links that was no longer needed in /usr/local/bin and I substituted /Library/Frameworks/Python.framework/Versions/3.8/bin by /opt/local/Library/Frameworks/Python.framework/Versions/3.8/bin in the PATH defined in ~/.bash_profile) Then finally I reloaded the main Python pakages that I was using (about ten that brought me 70 sub-packages) Note that pip (python package installer) must apparently be used via sudo if you want the packages to be installed in the right place (/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages) because the Python files and directories brought by Macport belong to root/wheel unlike those of the python.org installer who belong to root/admin (and as a MacOS administrator we belong to the admin group and not to wheel group) And since I didn't want to change the group or the file protection brought back by Python Macports, sudo was the simplest solution. @ Uli Wienands: I was also under Snow Leopard (10.6) before switching to El Capitan (10.11) because too many applications could no longer be updated. To keep the possibility of running PPC applications under El Capitan I installed a Snow Leopard Server in a VMWare Fusion, and it works :-) But it is true that there is a risk when updating Macports, it can be limited by making prior backups with Time Machine or Carbon Copy Cloner.
