BaseSettings: Customization of field value priority via Config

[espdev]

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Feature Request

Currently, there is field value priority (from the docs):

In the case where a value is specified for the same Settings field in multiple ways, the selected value is determined as follows (in descending order of priority):

1. Arguments passed to the Settings class initialiser.
2. Environment variables, e.g. my_prefix_special_function as described above.
3. Variables loaded from a dotenv (.env) file.
4. The default field values for the Settings model.

However, in some cases it would be nice to swap 1 and (2,3) priorities. For example, I would like to create the configuration system based on config files (YAML, TOML, INI, etc) and env vars where envvars/dotenv have highest priority (env vars override values from config files that looks reasonable in some cases just like now env vars (2) override dotenv file (3)).

It might look something like this:

class Settings(BaseSettings):
    ...

s = Settings(**load_from_config_file(config_path))

In this case values from config file will override values from env vars.

Currently, the default behavior cannot be changed without subclassing BaseSettings class and overriding _build_values method. This is not mentioned in the current docs but previously it was mentioned (see pydantic/pydantic#340, pydantic/pydantic#341, pydantic/pydantic#343).

Would you mind considering the customization of this behavior via Config of BaseSettings model?

[layday]

This was briefly discussed deep in a PR: pydantic/pydantic#1011 (comment).

[layday]

Perhaps a way this would work would be to introduce a new Config option for BaseSettings, e.g. env_has_prio which would default to False. If True the order would become 2, 3, 1, 4. I don't think there is a use case for lifting .env above env vars.

[samuelcolvin]

See my suggestion for a more powerful way to achieve this: pydantic/pydantic#2107 (comment)

[hramezani]

You can do it by change source priority in pydantic-settings