Python setup

macOS 15+ · signed Apple silicon app

Python bindings for the Slab runtime, using ctypes on the shared library (libslab.dylib). No compiled extension and no required dependencies; NumPy is used when installed.

Install

The macOS release contains the library and the Python package side by side:

macos/
  libslab.dylib
  slab.h
  python/slab/

Add macos/python to PYTHONPATH (or copy python/slab into your project). The package finds libslab.dylib two folders up. Elsewhere, point it at the library with slab.load("/path/to/libslab.dylib") or the SLAB_LIBRARY environment variable.

Use

import slab

cfg = slab.Config(models_dir="models", license=open("license.txt").read())
session = slab.Session(cfg, "classifier.slab")

out = session.run(slab.Input(frame=slab.Frame.open("photo.jpg")))
for c in out.top_k(5):
    print(c.label or c.class_id, c.score)

Streaming text:

inp = slab.Input(prompt="Describe this image.")
for piece in session.generate(inp):
    print(piece, end="")

Examples: classify, faces, tensors, chat, camera (live detection with OpenCV).

API

The objects are the same as in Slab's C and C+ APIs: Config, Session, Frame, Input, Output. In Python:

Python	Behavior
Errors	Failed calls raise `slab.SlabError` (`code`, `message`). License problems raise `slab.LicenseError` with a `detail` reason code.
`Session(cfg, path)`	Creates and opens in one step. Keyword options: `backend`, `warmup`, `context_length`.
`session.run(inp)`	Returns an `Output` (or fills the one passed).
`session.generate(inp, out)`	Iterator over text pieces; `out` holds the totals afterwards. `session.cancel()` works from any thread.
`input.set_tensor(index_or_name, data, dtype)`	`data`: NumPy array, `array.array`, raw bytes or a list. Always copied.
`out.array(i)`, `out.numpy(i)`, `out.shape(i)`	Copies of output tensors.
`out.top_k(k)`, `out.boxes(...)`	Lists of `Classification` and `Box` (with `landmarks`).
`frame.crop(x, y, w, h)`	A view sharing the parent's pixels; the parent is kept alive.
Objects	Freed by garbage collection, or at once with `close()` / `with`.

Licensing on macOS

On macOS a runtime license is bound to a signed app: its bundle ID and Keychain group. A plain python3 command is not a signed app, so with a customer build of libslab.dylib the license is refused and models do not open. Use the bindings inside a signed macOS app that embeds Python, or with a development build of the library.