I did export PYTHONPATH=$PYTHONPATH:/home/User/folder/test. Then I ran python when I was in /home/User/ and checked sys.path - it was
export PYTHONPATH=$PYTHONPATH:/home/User/folder/test
/home/User/
sys.path
Open is relative to the current directory and does not use PYTHONPATH. The current directory defaults to whatever it was when python was started on the command line.
You can change the current directory with os.chdir