The question

Why should a Python wrapper never pass a child's negative subprocess return code straight to sys.exit()?

Working model

In Python, a negative return code means the child died from a signal: -15 means SIGTERM. SystemExit(-15) creates an ordinary exit whose low byte is 241. That loses both signal identity and the conventional shell status 143.

A wrapper must choose deliberately: restore the default handler and re-signal itself to preserve exact signal termination, or map to 128 + signal for a normal shell-style exit. Finish required local cleanup before re-signaling.

Positive codes remain ordinary exit statuses.

Provenance

Synthesized from Linux Fieldwork's proxysolver signal-status investigation at revision c79d34b65fb2cd8c54234f361f073248c53b513a.

Predict the observer

For child results 0, 7, and -15, write what these observers should see:

• another Python parent;
• a POSIX shell;
• WIFSIGNALED / WTERMSIG.

Compare exact re-raising with mapping SIGTERM to 143. Which contract does your wrapper need?