Sandbox — separate a working folder from a security boundary

What this term means

A sandbox restricts what a process can observe or modify, usually by constraining system calls, filesystem access, credentials, namespaces, permissions or network routes. A temporary folder, Python virtual environment, Git branch and browser private window are not by themselves security sandboxes for hostile programs.

Safe contrast: scratch directory, not isolation

from pathlib import Path
from tempfile import TemporaryDirectory

with TemporaryDirectory() as root:
    workspace = Path(root)
    file = workspace / "sample.txt"
    file.write_text("training data", encoding="utf-8")
    assert file.read_text(encoding="utf-8") == "training data"

This snippet organizes disposable trusted work. It does not prevent the same Python process from reading other paths accessible to its OS user. Do not execute unknown binaries or unreviewed scripts inside it and assume safety.

Design a real boundary

For an offline lesson viewer, the safe default is render inert lesson text. If code must be executed, prefer a separately provisioned operating-system sandbox or VM, restrict writable mounts, block network egress where not required, use an unprivileged identity, set CPU/time/memory limits and provide no credentials. The exact controls depend on Android/Termux versus desktop Linux versus Windows. A phone app's Android sandbox is not equivalent to rootless Linux namespaces.

Adversarial verification

1. Make a permissions table: lesson reader can read packaged lessons but cannot write outside an approved scratch area.
2. Attempt a harmless write into a deliberately protected test directory inside a disposable test environment and expect a denied operation.
3. Confirm the sandbox cannot reach an example local service when network access is disabled. Do not probe systems you do not own.
4. Confirm that timeout/cancellation stops runaway work, and document what happens to children.
5. Review whether diagnostic logs or exceptions expose secrets from the host.

Evidence

List the real isolation mechanism, OS version, mount/network privileges and both positive and denied tests. If you only used TemporaryDirectory, describe it as cleanup, not isolation.