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Settings Management

Pydantic Settings provides optional Pydantic features for loading a settings or config class from environment variables or secrets files.

Installation

Installation is as simple as:

pip install pydantic-settings

Usage

If you create a model that inherits from BaseSettings, the model initialiser will attempt to determine the values of any fields not passed as keyword arguments by reading from the environment. (Default values will still be used if the matching environment variable is not set.)

This makes it easy to:

  • Create a clearly-defined, type-hinted application configuration class
  • Automatically read modifications to the configuration from environment variables
  • Manually override specific settings in the initialiser where desired (e.g. in unit tests)

For example:

from typing import Any, Callable, Set

from pydantic import (
    AliasChoices,
    AmqpDsn,
    BaseModel,
    Field,
    ImportString,
    PostgresDsn,
    RedisDsn,
)

from pydantic_settings import BaseSettings, SettingsConfigDict


class SubModel(BaseModel):
    foo: str = 'bar'
    apple: int = 1


class Settings(BaseSettings):
    auth_key: str = Field(validation_alias='my_auth_key')  # (1)!

    redis_dsn: RedisDsn = Field(
        'redis://user:pass@localhost:6379/1',
        validation_alias=AliasChoices('service_redis_dsn', 'redis_url'),  # (2)!
    )
    pg_dsn: PostgresDsn = 'postgres://user:pass@localhost:5432/foobar'
    amqp_dsn: AmqpDsn = 'amqp://user:pass@localhost:5672/'

    special_function: ImportString[Callable[[Any], Any]] = 'math.cos'  # (3)!

    # to override domains:
    # export my_prefix_domains='["foo.com", "bar.com"]'
    domains: Set[str] = set()

    # to override more_settings:
    # export my_prefix_more_settings='{"foo": "x", "apple": 1}'
    more_settings: SubModel = SubModel()

    model_config = SettingsConfigDict(env_prefix='my_prefix_')  # (4)!


print(Settings().model_dump())
"""
{
    'auth_key': 'xxx',
    'redis_dsn': Url('redis://user:pass@localhost:6379/1'),
    'pg_dsn': MultiHostUrl('postgres://user:pass@localhost:5432/foobar'),
    'amqp_dsn': Url('amqp://user:pass@localhost:5672/'),
    'special_function': math.cos,
    'domains': set(),
    'more_settings': {'foo': 'bar', 'apple': 1},
}
"""

  1. The environment variable name is overridden using validation_alias. In this case, the environment variable my_auth_key will be read instead of auth_key.

    Check the Field documentation for more information.

  2. The AliasChoices class allows to have multiple environment variable names for a single field. The first environment variable that is found will be used.

    Check the AliasChoices for more information.

  3. The ImportString class allows to import an object from a string. In this case, the environment variable special_function will be read and the function math.cos will be imported.

  4. The env_prefix config setting allows to set a prefix for all environment variables.

    Check the Environment variable names documentation for more information.

Environment variable names

By default, the environment variable name is the same as the field name.

You can change the prefix for all environment variables by setting the env_prefix config setting, or via the _env_prefix keyword argument on instantiation:

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_prefix='my_prefix_')

    auth_key: str = 'xxx'  # will be read from `my_prefix_auth_key`

Note

The default env_prefix is '' (empty string).

If you want to change the environment variable name for a single field, you can use an alias.

There are two ways to do this:

  • Using Field(alias=...) (see api_key above)
  • Using Field(validation_alias=...) (see auth_key above)

Check the Field aliases documentation for more information about aliases.

Case-sensitivity

By default, environment variable names are case-insensitive.

If you want to make environment variable names case-sensitive, you can set the case_sensitive config setting:

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(case_sensitive=True)

    redis_host: str = 'localhost'

When case_sensitive is True, the environment variable names must match field names (optionally with a prefix), so in this example redis_host could only be modified via export redis_host. If you want to name environment variables all upper-case, you should name attribute all upper-case too. You can still name environment variables anything you like through Field(validation_alias=...).

Case-sensitivity can also be set via the _case_sensitive keyword argument on instantiation.

In case of nested models, the case_sensitive setting will be applied to all nested models.

import os

from pydantic import ValidationError

from pydantic_settings import BaseSettings


class RedisSettings(BaseSettings):
    host: str
    port: int


class Settings(BaseSettings, case_sensitive=True):
    redis: RedisSettings


os.environ['redis'] = '{"host": "localhost", "port": 6379}'
print(Settings().model_dump())
#> {'redis': {'host': 'localhost', 'port': 6379}}
os.environ['redis'] = '{"HOST": "localhost", "port": 6379}'  # (1)!
try:
    Settings()
except ValidationError as e:
    print(e)
    """
    2 validation errors for RedisSettings
    host
      Field required [type=missing, input_value={'HOST': 'localhost', 'port': 6379}, input_type=dict]
        For further information visit https://errors.pydantic.dev/2/v/missing
    HOST
      Extra inputs are not permitted [type=extra_forbidden, input_value='localhost', input_type=str]
        For further information visit https://errors.pydantic.dev/2/v/extra_forbidden
    """
  1. Note that the host field is not found because the environment variable name is HOST (all upper-case).

Note

On Windows, Python's os module always treats environment variables as case-insensitive, so the case_sensitive config setting will have no effect - settings will always be updated ignoring case.

Parsing environment variable values

For most simple field types (such as int, float, str, etc.), the environment variable value is parsed the same way it would be if passed directly to the initialiser (as a string).

Complex types like list, set, dict, and sub-models are populated from the environment by treating the environment variable's value as a JSON-encoded string.

Another way to populate nested complex variables is to configure your model with the env_nested_delimiter config setting, then use an environment variable with a name pointing to the nested module fields. What it does is simply explodes your variable into nested models or dicts. So if you define a variable FOO__BAR__BAZ=123 it will convert it into FOO={'BAR': {'BAZ': 123}} If you have multiple variables with the same structure they will be merged.

As an example, given the following environment variables: 

# your environment
export V0=0
export SUB_MODEL='{"v1": "json-1", "v2": "json-2"}'
export SUB_MODEL__V2=nested-2
export SUB_MODEL__V3=3
export SUB_MODEL__DEEP__V4=v4

You could load them into the following settings model:

from pydantic import BaseModel

from pydantic_settings import BaseSettings, SettingsConfigDict


class DeepSubModel(BaseModel):
    v4: str


class SubModel(BaseModel):
    v1: str
    v2: bytes
    v3: int
    deep: DeepSubModel


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_nested_delimiter='__')

    v0: str
    sub_model: SubModel


print(Settings().model_dump())
"""
{
    'v0': '0',
    'sub_model': {'v1': 'json-1', 'v2': b'nested-2', 'v3': 3, 'deep': {'v4': 'v4'}},
}
"""

env_nested_delimiter can be configured via the model_config as shown above, or via the _env_nested_delimiter keyword argument on instantiation.

JSON is only parsed in top-level fields, if you need to parse JSON in sub-models, you will need to implement validators on those models.

Nested environment variables take precedence over the top-level environment variable JSON (e.g. in the example above, SUB_MODEL__V2 trumps SUB_MODEL).

You may also populate a complex type by providing your own source class.

import json
import os
from typing import Any, List, Tuple, Type

from pydantic.fields import FieldInfo

from pydantic_settings import (
    BaseSettings,
    EnvSettingsSource,
    PydanticBaseSettingsSource,
)


class MyCustomSource(EnvSettingsSource):
    def prepare_field_value(
        self, field_name: str, field: FieldInfo, value: Any, value_is_complex: bool
    ) -> Any:
        if field_name == 'numbers':
            return [int(x) for x in value.split(',')]
        return json.loads(value)


class Settings(BaseSettings):
    numbers: List[int]

    @classmethod
    def settings_customise_sources(
        cls,
        settings_cls: Type[BaseSettings],
        init_settings: PydanticBaseSettingsSource,
        env_settings: PydanticBaseSettingsSource,
        dotenv_settings: PydanticBaseSettingsSource,
        file_secret_settings: PydanticBaseSettingsSource,
    ) -> Tuple[PydanticBaseSettingsSource, ...]:
        return (MyCustomSource(settings_cls),)


os.environ['numbers'] = '1,2,3'
print(Settings().model_dump())
#> {'numbers': [1, 2, 3]}

Dotenv (.env) support

Dotenv files (generally named .env) are a common pattern that make it easy to use environment variables in a platform-independent manner.

A dotenv file follows the same general principles of all environment variables, and it looks like this:

.env
# ignore comment
ENVIRONMENT="production"
REDIS_ADDRESS=localhost:6379
MEANING_OF_LIFE=42
MY_VAR='Hello world'

Once you have your .env file filled with variables, pydantic supports loading it in two ways:

  1. Setting the env_file (and env_file_encoding if you don't want the default encoding of your OS) on model_config in the BaseSettings class:
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file='.env', env_file_encoding='utf-8')
  1. Instantiating the BaseSettings derived class with the _env_file keyword argument (and the _env_file_encoding if needed):
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file='.env', env_file_encoding='utf-8')


settings = Settings(_env_file='prod.env', _env_file_encoding='utf-8')

In either case, the value of the passed argument can be any valid path or filename, either absolute or relative to the current working directory. From there, pydantic will handle everything for you by loading in your variables and validating them.

Note

If a filename is specified for env_file, Pydantic will only check the current working directory and won't check any parent directories for the .env file.

Even when using a dotenv file, pydantic will still read environment variables as well as the dotenv file, environment variables will always take priority over values loaded from a dotenv file.

Passing a file path via the _env_file keyword argument on instantiation (method 2) will override the value (if any) set on the model_config class. If the above snippets were used in conjunction, prod.env would be loaded while .env would be ignored.

If you need to load multiple dotenv files, you can pass multiple file paths as a tuple or list. The files will be loaded in order, with each file overriding the previous one.

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        # `.env.prod` takes priority over `.env`
        env_file=('.env', '.env.prod')
    )

You can also use the keyword argument override to tell Pydantic not to load any file at all (even if one is set in the model_config class) by passing None as the instantiation keyword argument, e.g. settings = Settings(_env_file=None).

Because python-dotenv is used to parse the file, bash-like semantics such as export can be used which (depending on your OS and environment) may allow your dotenv file to also be used with source, see python-dotenv's documentation for more details.

Pydantic settings consider extra config in case of dotenv file. It means if you set the extra=forbid (default) on model_config and your dotenv file contains an entry for a field that is not defined in settings model, it will raise ValidationError in settings construction.

For compatibility with pydantic 1.x BaseSettings you should use extra=ignore: 

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file='.env', extra='ignore')

Secrets

Placing secret values in files is a common pattern to provide sensitive configuration to an application.

A secret file follows the same principal as a dotenv file except it only contains a single value and the file name is used as the key. A secret file will look like the following:

/var/run/database_password
super_secret_database_password

Once you have your secret files, pydantic supports loading it in two ways:

  1. Setting the secrets_dir on model_config in a BaseSettings class to the directory where your secret files are stored.
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(secrets_dir='/var/run')

    database_password: str
  1. Instantiating the BaseSettings derived class with the _secrets_dir keyword argument:
settings = Settings(_secrets_dir='/var/run')

In either case, the value of the passed argument can be any valid directory, either absolute or relative to the current working directory. Note that a non existent directory will only generate a warning. From there, pydantic will handle everything for you by loading in your variables and validating them.

Even when using a secrets directory, pydantic will still read environment variables from a dotenv file or the environment, a dotenv file and environment variables will always take priority over values loaded from the secrets directory.

Passing a file path via the _secrets_dir keyword argument on instantiation (method 2) will override the value (if any) set on the model_config class.

Use Case: Docker Secrets

Docker Secrets can be used to provide sensitive configuration to an application running in a Docker container. To use these secrets in a pydantic application the process is simple. More information regarding creating, managing and using secrets in Docker see the official Docker documentation.

First, define your Settings class with a SettingsConfigDict that specifies the secrets directory.

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(secrets_dir='/run/secrets')

    my_secret_data: str

Note

By default Docker uses /run/secrets as the target mount point. If you want to use a different location, change Config.secrets_dir accordingly.

Then, create your secret via the Docker CLI 

printf "This is a secret" | docker secret create my_secret_data -

Last, run your application inside a Docker container and supply your newly created secret 

docker service create --name pydantic-with-secrets --secret my_secret_data pydantic-app:latest

Field value priority

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. Variables loaded from the secrets directory.
  5. The default field values for the Settings model.

Customise settings sources

If the default order of priority doesn't match your needs, it's possible to change it by overriding the settings_customise_sources method of your Settings .

settings_customise_sources takes four callables as arguments and returns any number of callables as a tuple. In turn these callables are called to build the inputs to the fields of the settings class.

Each callable should take an instance of the settings class as its sole argument and return a dict.

Changing Priority

The order of the returned callables decides the priority of inputs; first item is the highest priority.

from typing import Tuple, Type

from pydantic import PostgresDsn

from pydantic_settings import BaseSettings, PydanticBaseSettingsSource


class Settings(BaseSettings):
    database_dsn: PostgresDsn

    @classmethod
    def settings_customise_sources(
        cls,
        settings_cls: Type[BaseSettings],
        init_settings: PydanticBaseSettingsSource,
        env_settings: PydanticBaseSettingsSource,
        dotenv_settings: PydanticBaseSettingsSource,
        file_secret_settings: PydanticBaseSettingsSource,
    ) -> Tuple[PydanticBaseSettingsSource, ...]:
        return env_settings, init_settings, file_secret_settings


print(Settings(database_dsn='postgres://postgres@localhost:5432/kwargs_db'))
#> database_dsn=MultiHostUrl('postgres://postgres@localhost:5432/kwargs_db')

By flipping env_settings and init_settings, environment variables now have precedence over __init__ kwargs.

Adding sources

As explained earlier, pydantic ships with multiples built-in settings sources. However, you may occasionally need to add your own custom sources, settings_customise_sources makes this very easy:

import json
from pathlib import Path
from typing import Any, Dict, Tuple, Type

from pydantic.fields import FieldInfo

from pydantic_settings import (
    BaseSettings,
    PydanticBaseSettingsSource,
    SettingsConfigDict,
)


class JsonConfigSettingsSource(PydanticBaseSettingsSource):
    """
    A simple settings source class that loads variables from a JSON file
    at the project's root.

    Here we happen to choose to use the `env_file_encoding` from Config
    when reading `config.json`
    """

    def get_field_value(
        self, field: FieldInfo, field_name: str
    ) -> Tuple[Any, str, bool]:
        encoding = self.config.get('env_file_encoding')
        file_content_json = json.loads(
            Path('tests/example_test_config.json').read_text(encoding)
        )
        field_value = file_content_json.get(field_name)
        return field_value, field_name, False

    def prepare_field_value(
        self, field_name: str, field: FieldInfo, value: Any, value_is_complex: bool
    ) -> Any:
        return value

    def __call__(self) -> Dict[str, Any]:
        d: Dict[str, Any] = {}

        for field_name, field in self.settings_cls.model_fields.items():
            field_value, field_key, value_is_complex = self.get_field_value(
                field, field_name
            )
            field_value = self.prepare_field_value(
                field_name, field, field_value, value_is_complex
            )
            if field_value is not None:
                d[field_key] = field_value

        return d


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file_encoding='utf-8')

    foobar: str

    @classmethod
    def settings_customise_sources(
        cls,
        settings_cls: Type[BaseSettings],
        init_settings: PydanticBaseSettingsSource,
        env_settings: PydanticBaseSettingsSource,
        dotenv_settings: PydanticBaseSettingsSource,
        file_secret_settings: PydanticBaseSettingsSource,
    ) -> Tuple[PydanticBaseSettingsSource, ...]:
        return (
            init_settings,
            JsonConfigSettingsSource(settings_cls),
            env_settings,
            file_secret_settings,
        )


print(Settings())
#> foobar='test'

Removing sources

You might also want to disable a source:

from typing import Tuple, Type

from pydantic import ValidationError

from pydantic_settings import BaseSettings, PydanticBaseSettingsSource


class Settings(BaseSettings):
    my_api_key: str

    @classmethod
    def settings_customise_sources(
        cls,
        settings_cls: Type[BaseSettings],
        init_settings: PydanticBaseSettingsSource,
        env_settings: PydanticBaseSettingsSource,
        dotenv_settings: PydanticBaseSettingsSource,
        file_secret_settings: PydanticBaseSettingsSource,
    ) -> Tuple[PydanticBaseSettingsSource, ...]:
        # here we choose to ignore arguments from init_settings
        return env_settings, file_secret_settings


try:
    Settings(my_api_key='this is ignored')
except ValidationError as exc_info:
    print(exc_info)
    """
    1 validation error for Settings
    my_api_key
      Field required [type=missing, input_value={}, input_type=dict]
        For further information visit https://errors.pydantic.dev/2/v/missing
    """