Original issue. Resolved in the reported scope. -P and PYTHONSAFEPATH control actual automatic path insertion, including script, command, module and interactive execution.

• Source and standard library: f39b054b9c8c.
• Verified October 5, 2026 on macOS 26.5.2 ARM64.
• RustPython 0.6.1 / Python 3.14.0.alpha and CPython 3.14.6, both ARM64.

Use absolute paths: set RP and CP to those executables and SRC to the matching RustPython source directory. Put the two files below in $SRC/repro_fixture and set CASE to that directory. The fixture directory name and absolute paths are shortened from the recorded inputs; the import checks and flags are unchanged.

CASE="$SRC/repro_fixture"
export RP CP SRC CASE
unset PYTHONPATH PYTHONHOME PYTHONWARNINGS PYTHONSTARTUP PYTHONSAFEPATH
export PYTHONDONTWRITEBYTECODE=1 LANG=C LC_ALL=C NO_COLOR=1 TERM=dumb
cd "$SRC"

value = "new-safe-path-fixture"

import sys
import os
import json
import importlib


def can_import(name):
    try:
        m = importlib.import_module(name)
        return m.value
    except ModuleNotFoundError:
        return False


print(
    json.dumps(
        {
            "safe_path": sys.flags.safe_path,
            "isolated": sys.flags.isolated,
            "path": sys.path,
            "cwd": os.getcwd(),
            "bare_import": can_import("safe_fixture"),
            "cwd_import": can_import("repro_fixture.safe_fixture"),
        },
        sort_keys=True,
    )
)

For the command-mode comparison:

RUSTPYTHONPATH="$SRC/Lib" "$RP" -B -c "$(cat "$CASE/safe_report.py")"
RUSTPYTHONPATH="$SRC/Lib" "$RP" -B -P -c "$(cat "$CASE/safe_report.py")"

"$CP" -B -c "$(cat "$CASE/safe_report.py")"
"$CP" -B -P -c "$(cat "$CASE/safe_report.py")"

The same recorded checks covered these invocation forms:

• Script: replace -c "$(cat "$CASE/safe_report.py")" with "$CASE/safe_report.py". The default prepends the script directory; -P suppresses that entry.
• Symlink: run a symlink to safe_report.py, with and without -P. The default entry resolves to the real script directory.
• Module: use -m safe_report. Set RUSTPYTHONPATH="$SRC/Lib:$CASE" for RustPython and PYTHONPATH="$CASE" for CPython so the module remains explicitly discoverable with -P.
• Environment flag: omit -P and set PYTHONSAFEPATH=1. An empty value leaves safe-path mode disabled; any nonempty value, including 0, enables it.
• Environment controls: -E ignores PYTHONSAFEPATH and explicit module-search environment variables. -I enables safe-path behavior and also ignores those variables.

For the interactive check, launch "$RP" -B -q with RUSTPYTHONPATH="$SRC/Lib", and separately "$CP" -B -q. Repeat with -P or PYTHONSAFEPATH=1. Enter the following in the actual terminal session:

import sys, os, json
print("REPL_RESULT=" + json.dumps({
    "safe_path": sys.flags.safe_path,
    "path": sys.path,
    "cwd": os.getcwd(),
}), flush=True)
os._exit(0)

TERM=dumb selected the basic REPL in both interpreters. Its fallback warning is expected; stdout and stderr are merged in the PTY transcript.

Both interpreters produced the following flag and fixture-import results in command mode:

default:
  safe_path = False
  isolated = 0
  path begins with ""
  bare_import = False
  cwd_import = "new-safe-path-fixture"

-P:
  safe_path = True
  isolated = 0
  path has no automatically inserted ""
  bare_import = False
  cwd_import = False

Each command-mode run exited 0 with empty stderr. Interpreter-specific standard-library entries differ, so the complete sys.path lists are not expected to be identical.

Script, symlink and PTY runs confirmed the same suppression of their automatic unsafe entries. Explicit entries supplied through RUSTPYTHONPATH or PYTHONPATH remained searchable under -P, including the module-mode fixture.

The 52 recorded processes had no timeouts. The four module-mode -E/-I runs exited 1 because they ignored the only explicit path to safe_report; those lookup failures are expected. The remaining runs exited 0.

At 746cb0493f73, the previously recorded command rejected -P and exited 1:

error: Found argument '-P' which wasn't expected, or isn't valid in this context

• PR #4611: connect -P, the environment and safe_path.
• PR #5049: make automatic insertion conditional on safe_path.
• PR #8605: resolve script paths for insertion.

First fixing commit: not established.

Recorded executable SHA-256 values:

• RustPython: a40f4d564f9c53ffcc4ec27c1a61ae3261b68cf3286f511a2ad39fb7f60c9b99.

• CPython: 58eea46bd68c84e30980ca1133d1b0efb139c878a4934a519dba0846b74069ef.

• RustPython default and -P.

• CPython default and -P.

• Recorded fixture and recorded probe.

• All modes, environments and results.

• Historical record.

AI assistance: OpenAI Codex.