Configuration Files

pydantic-settings loads a settings class from environment variables or secrets files. Subclass BaseSettings and declare each setting as a type-hinted field. Any field you don't pass to the initializer gets its value from the environment, or its default when the variable isn't set. To read a .env file too, set env_file in model_config, and its values get validated like the rest.

configparser comes with Python. It reads a basic configuration language structured like Windows INI files, so end users can customize your program by editing a file. Read values with mapping access, config['section']['option'], which the docs prefer for new projects over the legacy get and set methods. Values always come back as strings, so convert them with getint(), getfloat(), and getboolean().

python-dotenv is for apps that take their configuration from environment variables. In development, setting each one yourself isn't practical, so call load_dotenv() before the rest of your code. It reads a .env file when there is one and adds its values to os.environ, so your code reads them with os.getenv() as if they came from the real environment.

Hydra is a framework for research and other complex applications. It builds a hierarchical configuration by composition, and you override it from config files and the command line. Decorate your entry point with @hydra.main() and point it at a YAML config. Then change a value with an argument like db.user=root. For options you switch between, like two databases, create a config group with one file per option, and pick one in the config's defaults list. With --multirun, one command runs your function once for each configuration you list.

Dynaconf reads settings from files in several formats, environment variables, and Vault or Redis. Start with dynaconf init -f toml, which creates config.py, settings.toml, and .secrets.toml. Then import settings from config in your code. TOML is its default and most recommended format. To give development and production their own sections in one file, set environments=True. In a Django app, django.conf.settings becomes a Dynaconf settings object, and in Flask, app.config does.

Keep settings that change between deployments out of your code. The twelve-factor app stores config in environment variables, and python-dotenv and Dynaconf both cite it. python-dotenv, pydantic-settings, and Dynaconf let the real environment win over files. load_dotenv() doesn't override variables already set, pydantic-settings ranks environment variables above .env and secrets files, and Dynaconf prioritizes environment variables over files. Keep secrets out of Git, too: add .env to your .gitignore, and dynaconf init adds .secrets.* there for you.