Activation doesn't set environment variables correctly

[demining]

I previously raised the issue that I can not install and activate fpylll on Ubuntu 18.04.5 LTS (bionic)
#214

I was unable to activate
When I run my script, I get the error:

python3 script.py
Traceback (most recent call last):
  File "script.py", line 35, in <module>
    from fpylll import LLL, BKZ, IntegerMatrix
ImportError: cannot import name 'LLL' from 'fpylll' (unknown location)
I raised the question earlier on askubuntu

https://askubuntu.com/questions/1363992/bin-sh-1-source-not-found/1363998?noredirect=1#comment2340523_1363998

I was answered by jpbrain

Activate only sets enviroment variables to point to the Libs and bootstrap.sh is a shell script. Take a look at https://github.com/fplll/fpylll/blob/master/bootstrap.sh onlines 33-39 and 50-55.Those lines set enviroment variables. -
So you need to set your enviroment correctly to be able to run it. what do you get with "env" and "env python"

What should I change in bootstrap.sh to set up the environment correctly?