tcc-venv

Give a uv/venv Python app a stable, codesigned macOS TCC identity — so Full Disk Access / Automation grants survive uv sync and Python upgrades, and the permission dialog shows a recognizable per-project name instead of python3.12.

macOS only for the privacy benefit. On Linux/Windows it degrades to a no-op passthrough so the same launcher name works everywhere.

Why macOS only? The privacy-grant-churn problem is specific to macOS TCC. The nearest analogues elsewhere are path-keyed, not signature-keyed: Windows Defender Firewall matches its allow rules by image path, and Linux AppArmor/SELinux confine by path — so a moving venv-python path can drift out from under those too. But the fix there is simply a stable launcher path, which the no-op python-tcc symlink already gives you on every platform; there is no codesigning, disclaim bootstrap, or privacy prompt involved off macOS.

The problem

macOS TCC (the privacy system behind Full Disk Access, Automation, Calendar, etc.) grants permissions to a specific binary identity — its path plus its code-signing identity. A Python interpreter created by uv lives at a churning, version-pinned path:

~/.local/share/uv/python/cpython-3.12.7-macos-aarch64-none/bin/python3.12

Grant that binary Full Disk Access, then run uv python upgrade or let uv sync pull a new patch release, and the path changes. To TCC it's now a different app: the grant silently stops applying and your tool starts getting "Operation not permitted" until you re-grant it by hand. The dialog also just says "python3.12", giving the user no idea which project is asking.

tcc-venv fixes both by interposing a tiny signed C launcher with a stable identity that you grant once:

<venv>/bin/python-tcc-<project>   # signed trampoline — the stable TCC identity
<venv>/bin/python-tcc             # -> python-tcc-<project> (uniform name for shebangs/control)

The launcher self-locates its venv, spawns <venv>/bin/python with your arguments, forwards signals, and propagates the exit code — staying the parent process so TCC attributes everything to it. To make that hold even when the launcher above it does not hand it a TCC identity (a GUI app, a terminal — anything that isn't launchd), it re-spawns a self-responsible copy of itself first (a "disclaim" bootstrap), so the stable signed identity owns the grant regardless of who started it. Re-running wrap after uv sync restores the identical signed bytes from a local cache, so the cdhash — and the grant — is unchanged.

Set TCC_VENV_CHDIR=1 to run from the project root (the venv's parent), or to a path to cd there — handy when the launcher gives an unpredictable working directory.

What it is not

It does not bypass or weaken TCC. You still grant access explicitly in System Settings; this only stops the identity from moving out from under that grant. It relies on undocumented TCC responsible-process inheritance and ad-hoc cdhash determinism, both of which can change across macOS releases — treat it as unofficial and verify on the macOS versions you ship to.

Tested: on macOS Darwin 25.5.0, both Full Disk Access and EventKit/Reminders access through a launchd-launched (no terminal ancestor) python-tcc-<project> attach the grant to that signed binary — TCC records it against the per-project binary path, not the python child — confirming the responsible-process inheritance this tool depends on. Re-confirm on the macOS versions you target.

Requirements

• macOS with the Xcode Command Line Tools (xcode-select --install) — the trampoline is compiled with cc client-side at wrap time.
• Python ≥ 3.11.
• A venv with a pyvenv.cfg (uv, python -m venv, pdm-in-venv mode — all fine).

Install

uvx tcc-venv wrap            # run without installing
# or
pipx install tcc-venv
# or
uv tool install tcc-venv

Usage

Run wrap once per venv, then point your launchers / shebangs at python-tcc.

With uv

cd my-project
uv sync                      # creates ./.venv
uvx tcc-venv wrap            # defaults to ./.venv

Because uv sync recreates the interpreter, re-run wrap after a sync — it restores the same identity from cache, so you do not re-grant:

uv sync && uvx tcc-venv wrap

With pdm

pdm can manage an in-project venv. Enable it, install, then wrap:

pdm config python.use_venv true
pdm install                  # creates ./.venv
uvx tcc-venv wrap .venv

With a bare venv

python3 -m venv .venv
.venv/bin/pip install -e .
uvx tcc-venv wrap .venv

Tip: python -m venv --prompt myapp .venv sets the friendly name used in the identity and the TCC dialog (otherwise the venv's parent directory name is used).

Grant the permission (once)

After wrap, the binary path is printed. Add that binary to the relevant pane:

System Settings → Privacy & Security → Full Disk Access → + → select <venv>/bin/python-tcc-<project>

Automation / Calendar / Reminders prompts appear on first use. From then on, run your app through the shim:

.venv/bin/python-tcc my_app.py
# or in a shebang:  #!/path/to/.venv/bin/python-tcc

Two ways to launch: wrap vs run

wrap + invoke the binary directly — leanest, for long-lived servers. Point the launcher straight at <venv>/bin/python-tcc-<project>; zero per-launch overhead, offline-safe. (Re-run wrap after uv sync.)

tcc-venv run — wrap-on-demand, then run anything under the identity. It builds and signs the launcher if missing, then execs your command as the TCC-responsible parent. The command can be uv run … (the launcher disclaims first, so identity still attaches to the stable binary), so you get uv's auto-sync without losing the grant:

tcc-venv run --cd-to-project uv run --frozen my_app.py
# or a module:  tcc-venv run -m my_app
# in a shebang (note env -S for the multi-token line):
#!/usr/bin/env -S uvx tcc-venv run --cd-to-project uv run --frozen

run discovers the nearest .venv from the cwd; pass --venv DIR for split layouts or an unpredictable cwd. --cd-to-project runs from the venv's parent. The convenience costs uvx/uv startup per launch — use the direct-binary path when latency matters.

Commands

Both commands accept --identifier-prefix PREFIX (default local.tcc-venv).

The identifier is <prefix>.<project>.<hash8>, where <prefix> defaults to local.tcc-venv (override with --identifier-prefix or $TCC_VENV_IDENTIFIER_PREFIX) and <hash8> is derived from the venv's real path so two projects with the same name never share a grant.

How it works (short version)

1. Compile trampoline.c once per architecture (cached, unsigned).
2. Copy it to <venv>/bin/python-tcc-<project> and ad-hoc codesign it with a stable --identifier.
3. Cache the signed bytes by identifier + source tag; on re-wrap, copy them back so the cdhash is byte-identical regardless of codesign version drift. (Upgrading tcc-venv to a changed trampoline changes the tag → new cdhash → re-grant once.)
4. Symlink python-tcc -> python-tcc-<project>.

Steps 1–3 are safe to run concurrently: several launchd daemons sharing a venv all start in the same second at boot, so each invocation stages into a private temp file, swaps the shim with an atomic rename, and skips the work entirely when the installed binary is already correct. (Before 0.2.2 they shared a fixed staging filename and deleted each other's, so the loser died — see the changelog.)

At runtime the trampoline resolves its own path → venv, refuses to run if a stray $VIRTUAL_ENV disagrees, re-spawns a self-responsible copy of itself (disclaim bootstrap) so its identity owns the grant under any launcher, optionally cds per $TCC_VENV_CHDIR, posix_spawns the venv's python, forwards signals, and returns the child's exit status (128 + signo on signal death). On non-macOS it's a plain exec of the venv python with no signing.

See AGENTS.md for the full design and invariants.

Changelog

0.2.2

Fixes a race between concurrent invocations. Every staging path was a fixed filename removed in a finally:, so two overlapping runs deleted each other's half-written file and the loser exited with a traceback — which cost a real boot when two launchd daemons sharing a venv started in the same second. Three sites were affected: the per-venv install, the machine-wide compile cache (where the racing peer is an unrelated project, not another run against your venv), and the signed-bytes cache. Also: python-tcc is now swapped with an atomic rename instead of unlink-then-create, which previously left a window in which the shim did not exist at all, and an already-correct install now short-circuits without writing anything.

No re-grant needed. This release does not touch trampoline.c, so the source tag, the signed-bytes cache key and the cdhash are all unchanged — existing Full Disk Access / Automation grants keep working.

License

MIT — see LICENSE.