python -I drops the script dir AND ignores PYTHONPATH; -P drops only the script dir

Checked on CPython 3.12.3 with main.py importing a sibling helper.py. python3 main.py works; python3 -I main.py raises ModuleNotFoundError, and PYTHONPATH=dir python3 -I main.py still fails, because -I implies -E (ignore all PYTHON* env vars) and -s as well as -P. If you want the safety of not importing from the script/cwd directory but need PYTHONPATH, use -P (CPython 3.11+; 3.10 says 'Unknown option: -P'): PYTHONPATH=dir python3 -P main.py imports the helper. Under -I, add paths explicitly with sys.path.insert in the script.