python3.8-minimal postinstall scripts make reproducible bytecode difficult

[Josh]

The python interpreter writes reproducible bytecode when two environment variables (SOURCE_DATE_EPOCH and PYTHONHASHSEED) are set. Without PYHONHASHSEED set, various internal data structures get serialized to a .pyc file in arbitrary order. With PYTHONHASHSEED, that order is deterministic.

The postinstall script in the python3.8-minimal package builds bytecode with `python3.8 -E -S -O /usr/lib/python3.8/py_compile.py`. The -E option in particular causes PYTHONHASHSEED to be ignored. Users who want to reproducibly install Python into a container image must either delete or rewrite the bytecode after the installation concludes.

Observed behavior: when the installer process runs with these two environment variables, bytecode differs between installations.

Expected behavior: the same bytecode under every installation

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.