Config Sources and Loaders

Config Sources

A ConfigSource is a dataclass describing how to load config values from a certain source. It serves as instructions for the corresponding Loader.

There are multiple config sources which support a heterogeneous set of use-cases:

• FileSource allows to load config data from files. Currently, yaml- , json-, and toml-format is supported. The filename can either be passed directly, via environment variable or via command line argument. The latter cases allow to easily configure multiple environments by having a separate file for each environment.

• EnvSource allows to load config data from environment variables and .env files. It supports to select the corresponding variables with allow- and deny-lists and with an optional prefix and optional custom separator for nested variables. The variable names are either inferred from the config name (see EnvSource for the rules) or can be explicitly mapped.

• CLArgSource allows to load config data from command line arguments. An optional prefix allows to select only parts of the arguments. Optional custom separator for nested command line arguments is also supported. The argument names are either inferred from the config name or can be explicitly mapped.

• DataSource allows to define constant config data. This can be very useful for unit tests, see Context Manager.

Furthermore, it is possible to define your own sources with a corresponding loader, see Extending ConfZ.

Loading Order

When defining config sources as keyword argument or class variable, it is possible to either provide a single source or a list of sources. In the latter case, config sources are loaded in the same order as in this list and later config values can override earlier ones.

If keyword arguments are provided to the constructor of a config class, they are read at the beginning and thus can be overridden by any config source.