So I did it, and when I type 'python --version' I got the 3.8 only for the session but when I try to compile it looks like he doesn't compile with the 3.8 because I get the error 'from urllib.request import urlopen ImportError: No module named request' wich is a module existing in python 3.8 but not in 2.7.
I tried changing the path to python for the whole system, don't change anything, exept the fact that 'python --version' tells me the version I wrote in the path.
It is not even compiling that way, in the contrary to the commande 'py -3.8 telemac2d.py file.cas'