Where are the files ??

In basthon console or notebook, I can create a file with usual python process

#create
fichier = open('test.txt','w')
fichier.write("test")
fichier.close()

fichier.open('test.txt',r)
for ligne in fichier:
    print(ligne)
fichier.close()

is ok

If i do not close the window, I can even read without recreating.

but

import os
os.listdir()

returns an empty list. If I use my browser and look at local storage, test.txt is nowhere in browser local storage

So... where can I find the file, and is there any possibility to make it downloadable ?

(I've read the doc and found only informations about auxiliary file, not about file created in Python)