lykn Python SDK

Python license validation SDK for applications protected by Lykn.

What this SDK provides

• Runtime license verification with LicenseValidator.
• RSA signature, validity period, hardware binding, and feature checks.
• CLI tools for verification, license inspection, hardware collection, and packaging.
• FastAPI dependencies for route-level license and feature enforcement.
• Packaging helpers for bundling protected Python applications with PyInstaller or Nuitka.

Installation

Install the base SDK:

pip install lykn

Install optional integrations when needed:

pip install lykn[fastapi]
pip install lykn[pack]

For local development from this repository:

cd sdk/python
pip install -e ".[dev]"

Verify a license

Use LicenseValidator with a project public key and a signed license file:

from lykn import LicenseValidator

validator = LicenseValidator(
    public_key="./public.pem",
    license_path="./license.lic",
    check_interval=300,
)

license_data = validator.start()
assert validator.has_feature("reports") is True
validator.stop()

LicenseValidator accepts either license_path or license_content. Set check_interval to a positive number of seconds to re-check the license in the background after start() is called.

Common methods:

• verify(required_features=None): validate once and return LicenseData.
• start(): validate once and start background re-checks when enabled.
• stop(): stop the background re-check loop.
• has_feature(feature): check whether the current license includes a feature.
• on_invalid(callback): register a callback for background validation failure.

License data

Successful validation returns a LicenseData object with these fields:

• id: license ID.
• subject: licensed user or organization information.
• plan: license plan code.
• plan_name: license plan display name.
• issued_at, not_before, not_after: license time window.
• hardware: optional hardware binding data.
• features: enabled feature list.
• limits: structured license limits such as max_users and max_devices.
• metadata: legacy custom metadata, kept for older licenses.

Validation can raise these SDK errors:

• LicenseFileError
• LicenseSignatureError
• LicenseExpiredError
• LicenseNotYetValidError
• HardwareMismatchError
• FeatureNotLicensedError

CLI

The lykn command is installed with the SDK.

Verify a license and require one or more features:

lykn verify --public-key ./public.pem --license ./license.lic --feature reports

Inspect a signed license payload without verifying it:

lykn inspect --license ./license.lic

Collect local hardware data for hardware-bound licenses:

lykn hardware-info --format json
lykn hardware-info --format table

Bundle a protected Python application:

lykn pack --project ./my-app --engine pyinstaller --entry main.py --out ./dist
lykn pack --project ./my-app --engine nuitka --module my_app --mode onefile

FastAPI

Install the FastAPI extra first:

pip install lykn[fastapi]

Use RequireLicense to require any valid license, or RequireFeatures to require specific licensed features:

from fastapi import Depends, FastAPI
from lykn import LicenseValidator
from lykn.contrib.fastapi import RequireFeatures, RequireLicense

validator = LicenseValidator(public_key="./public.pem", license_path="./license.lic")
app = FastAPI()

@app.get("/health/license")
def license_health(license_data=Depends(RequireLicense(validator))):
    return {"license": license_data.id}

@app.get("/reports")
def reports(license_data=Depends(RequireFeatures(validator, "reports"))):
    return {"plan": license_data.plan}

Invalid licenses or missing features return HTTP 403 from the dependency.

Packaging protected apps

Install the packaging extra first:

pip install lykn[pack]

lykn pack stages the project, includes common Lykn resources such as license.lic and public.pem when present, and delegates the build to PyInstaller or Nuitka.

Use CLI options for one-off builds:

lykn pack \
  --project ./my-app \
  --engine pyinstaller \
  --entry main.py \
  --mode onedir \
  --resource license.lic \
  --resource public.pem \
  --exclude .env \
  --name my-app

Or store defaults in pyproject.toml:

[tool.lykn.pack]
engine = "pyinstaller"
entry = "main.py"
out = "dist"
mode = "onedir"
resources = ["license.lic", "public.pem"]
exclude = [".env", ".env.*", ".git", "__pycache__"]
name = "my-app"
clean = true
extra_args = ["--noconfirm"]

CLI options override values from pyproject.toml.

Compatibility

• Python 3.10 or newer.
• Optional FastAPI integration requires fastapi>=0.100.
• Optional packaging support requires pyinstaller>=6.0 or nuitka>=2.0.