Configure and run a reproducible API

In this lesson you will configure and run a reproducible API. Work with the Equipment Rental API in the downloadable lab. The reference is a complete solution with separate lesson checks, so you can inspect the answer, make a deliberate local change and verify its behavior.

Reproducibility has three parts: the Python runtime, the resolved dependencies and explicit configuration. The lab uses Python 3.13 and requirements.lock, which pins the runtime and test packages together. Install them into a virtual environment so unrelated projects cannot change your results. Record your interpreter version along with the lock file; a list of package names alone cannot reproduce the environment.

Settings reads LAB_ environment variables. The database URL and token key are required for the integrated application, and a short key is rejected. They have no checked-in secret defaults. The hello application remains usable without a database or identity system. This separation lets you start with a tiny request while keeping the final application configuration deliberate. The local database test runner generates temporary credentials in memory, publishes the container only on loopback and removes it afterward. It never selects an existing database. A passing setup check proves the local contract, not readiness for an Internet deployment.

Worked source: equipment/settings.py, Settings.

Create .venv with python3.13 -m venv .venv; activate it and run python -m pip install -r requirements.lock. Run python --version and python run_checks.py -k lesson02. The check constructs settings with a valid synthetic key and rejects a short one. Full API startup also requires your own disposable LAB_DATABASE_URL and LAB_JWT_SECRET.

class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_prefix="LAB_", extra="ignore")
    database_url: str
    jwt_secret: str = Field(min_length=32)
    api_title: str = "Equipment Rental learning API"
    provider_url: str = "http://127.0.0.1:8787"

    @property
    def sync_url(self):
        return sync_url(self.database_url)

python run_checks.py -k lesson02