fastapiex-settings 0.0.1

Global settings runtime extension for FastAPIEx

fastapiex-settings

Process-global settings declaration and resolution runtime based on Pydantic v2.

Installation

uv add fastapiex-settings

Public API (Only These Are Exported)

from fastapiex.settings import (
    BaseSettings,
    Settings,
    SettingsMap,
    GetSettings,
    GetSettingsMap,
    SettingsRef,
    init_settings,
    reload_settings,
    exceptions,
)

No other symbol is part of the package root public API.

Quick Start

from pydantic import Field
from fastapiex.settings import (
    BaseSettings,
    Settings,
    SettingsMap,
    GetSettings,
    GetSettingsMap,
    init_settings,
    reload_settings,
)


@Settings("app")
class AppSettings(BaseSettings):
    title: str = "demo"
    debug: bool = False


@SettingsMap("services")
class ServiceSettings(BaseSettings):
    host: str
    port: int = Field(ge=1, le=65535)


init_settings(settings_path="settings.yaml")

title = GetSettings("app", field="title")
services = GetSettingsMap(ServiceSettings)  # dict[str, ServiceSettings]
api_host = GetSettings("services.api", field="host")
reload_settings(reason="manual-refresh")

Public API Reference

BaseSettings

class BaseSettings(pydantic.BaseModel): ...

• Base class for declaration models.
• Inheriting this class does not register anything by itself.

Settings

@overload
def Settings(model: type[BaseSettings], /) -> type[BaseSettings]: ...

@overload
def Settings(path: str | None = None, /) -> Callable[[type[BaseSettings]], type[BaseSettings]]: ...

Role:

• Declare an object section.

Section name resolution order:

1. explicit decorator path
2. model __section__ if non-empty
3. snake_case class name

Accepted forms:

• @Settings
• @Settings("father.son")
• Settings(MyModel) (functional form)

SettingsMap

@overload
def SettingsMap(model: type[BaseSettings], /) -> type[BaseSettings]: ...

@overload
def SettingsMap(path: str | None = None, /) -> Callable[[type[BaseSettings]], type[BaseSettings]]: ...

Role:

• Declare a map section (shape like dict[str, Model]).

Accepted forms and section naming:

• Same behavior as Settings.

GetSettings

def GetSettings(
    target: str | type[object] | None = None,
    *,
    field: str | None = None,
    default: object = _NO_DEFAULT,
) -> Any

Role:

• Resolve settings values from the current typed snapshot.

Parameters:

• target:
  • str: dotted path, for example "app" / "father.son" / "services.api".
  • type: type-category injection; must match exactly one declared section.
  • None: only useful with default (otherwise unresolved).
• field:
  • optional dotted sub-path applied after target is resolved.
  • blank string is invalid.
• default:
  • returned as the whole query fallback value.
  • not projected by field.

Important semantics:

• Read chain: registered lookup -> rediscover+lookup -> default -> error.
• Incomplete path returns the current node as-is (model/dict/scalar/list element).
• Mapping type target (dict, Mapping) resolves only when exactly one @SettingsMap section exists.
• Returned objects are live runtime references (mutable); changes affect subsequent reads in the same process.

GetSettingsMap

def GetSettingsMap(
    target: str | type[object] | None = None,
    *,
    default: object = _NO_DEFAULT,
) -> Mapping[str, Any]

Role:

• Resolve settings as mapping-only API.

Parameters:

• target:
  • same semantics as GetSettings.
• default:
  • whole-query fallback value.
  • must be mapping when fallback path is used.

Behavior:

• Final value must be mapping; otherwise SettingsResolveError.
• Returned mapping is a live runtime reference (mutable), not a defensive copy.

SettingsRef

@dataclass(frozen=True)
class SettingsRef:
    target: str | type[object] | None
    field: str | None = None
    default: object = _NO_DEFAULT

    def get(self) -> Any: ...
    @property
    def value(self) -> Any: ...
    def __call__(self) -> Any: ...

Role:

• Lazy settings query descriptor.

Behavior:

• get(), .value, and () perform the same runtime resolve.
• Resolution semantics are identical to GetSettings.

init_settings

def init_settings(
    *,
    settings_path: str | Path | None = None,
    env_prefix: str | None = None,
) -> BaseModel

Role:

• Initialize process-global source and snapshot.

Parameter behavior:

• settings_path:
  • explicit bootstrap path.
  • only overrides the initial read of FASTAPIEX__SETTINGS__PATH.
  • does not lock source selection after bootstrap.
• env_prefix:
  • business env prefix override.
  • None means read from FASTAPIEX__SETTINGS__ENV_PREFIX.
  • non-empty value is treated as raw string prefix and removed from env key names.

Bootstrap source order:

• settings_path arg
• FASTAPIEX__SETTINGS__PATH
• FASTAPIEX__BASE_DIR + /settings.yaml
• ./settings.yaml

Runtime source switch:

• after each yaml read, manager checks merged live snapshot key FastAPIEx.settings.path (fastapiex.settings.path) and switches yaml source to that path when changed.
• this key is treated as an ordinary snapshot key (LWW + priority), not a dedicated control state branch.

Re-init behavior:

• Re-initializing with a different resolved source raises RuntimeError.

reload_settings

def reload_settings(*, reason: str = "manual") -> BaseModel

Role:

• Trigger a manual runtime refresh of current settings source.

Behavior:

• Calls manager-level reload flow.
• reason is logging context string.

exceptions

from fastapiex.settings import exceptions

Module members:

• exceptions.SettingsError
• exceptions.SettingsRegistrationError
• exceptions.SettingsValidationError
• exceptions.SettingsResolveError

Runtime Semantics

Registration

• Only @Settings / @SettingsMap register sections.
• Undecorated BaseSettings subclasses are ignored by registry discovery.
• Section paths under FASTAPIEX.* are reserved and rejected (case-insensitive).
• Registration stores section paths as declared (case-preserving), independent from runtime CASE_SENSITIVE.
• If multiple declared paths differ only by case, case-insensitive string lookups are ambiguous and fail; type-target lookups remain exact.

Source Loading

Sources:

• yaml (settings.yaml)
• .env file
• process os.environ

Merge strategy:

• LWW (last-write-wins by source update time)
• if timestamps tie: env > .env > yaml

Runtime reload:

• yaml may refresh by mode.
• .env and process env are loaded once at init time and not re-ingested by runtime yaml reload.
• when yaml source switches by FastAPIEx.settings.path, only yaml source is switched/reloaded; .env stays from the bootstrap directory.
• this is intentional by convention: .env is treated as an environment-variable generator, and runtime business env should be stable unless explicitly opted in.

Opt-in .env runtime sync (advanced):

• This is not part of the package-root public API. Use manager helper explicitly:

from fastapiex.settings import reload_settings
from fastapiex.settings.manager import register_source_sync

# include `.env` in runtime reload passes
register_source_sync("dotenv", sync_on_reload=True)

# optional: also follow `fastapiex.settings.path` source switches
register_source_sync("dotenv", sync_on_path_switch=True)

# optional: force one immediate re-ingest after enabling sync
reload_settings(reason="enable-dotenv-sync")

Parameter meaning:

• source="dotenv": target .env source behavior.
• sync_on_reload=True: re-read .env during reload pass (RELOAD=on_change|always, and manual reload_settings).
• sync_on_path_switch=True: when runtime settings file path switches, also re-read .env from the new settings directory.
• read_snapshot: normally omitted; keep default reader unless you are replacing source IO behavior.

Monkeypatch / Black Magic

GetSettings / GetSettingsMap expose mutable live objects by design.

Recommended safety flow when manually patching settings at runtime:

• before monkeypatching, set FastAPIEx.settings.reload (fastapiex.settings.reload) to off.
• perform the manual mutation.
• when done and you want to restore canonical values from configured sources, call reload_settings(reason="...").

Runtime Controls (FASTAPIEX__*)

Plain-key behavior:

• FASTAPIEX__* keys are ingested into live snapshot as plain keys under fastapiex.*.
• they are readable via GetSettings("fastapiex....").
• declaration is still forbidden: users cannot declare @Settings("fastapiex...") / @SettingsMap("fastapiex...").
• mixed-case keys from file/env (for example FastAPIEx.Settings.Reload) are normalized into canonical fastapiex.*.

Supported controls:

• FASTAPIEX__SETTINGS__PATH
• FASTAPIEX__BASE_DIR
• FASTAPIEX__SETTINGS__ENV_PREFIX
• FASTAPIEX__SETTINGS__CASE_SENSITIVE
• FASTAPIEX__SETTINGS__RELOAD

FASTAPIEX__SETTINGS__ENV_PREFIX rules:

• cannot start with FASTAPIEX__.
• empty prefix means plain keys are considered business keys.
• non-empty prefix is stripped as raw string.
• prefix matching follows runtime case mode: case-insensitive when CASE_SENSITIVE=false, exact when CASE_SENSITIVE=true.

Equivalent examples (all readable by GetSettings("one")):

• FASTAPIEX__SETTINGS__ENV_PREFIX=SOME_CUSTOM_PREFIX__ + SOME_CUSTOM_PREFIX__ONE=1
• FASTAPIEX__SETTINGS__ENV_PREFIX=SOME_CUSTOM_PREFIX_ + SOME_CUSTOM_PREFIX_ONE=1
• FASTAPIEX__SETTINGS__ENV_PREFIX=SOME_CUSTOM_PREFIX + SOME_CUSTOM_PREFIXONE=1
• empty prefix + ONE=1

Env split semantics:

• delimiter is __
• FOO___BAR -> ["FOO", "_BAR"]
• keys that produce empty segments are ignored (for example FOO____BAR, __X, X__)

Case Sensitivity

Control:

• FASTAPIEX__SETTINGS__CASE_SENSITIVE=true|false (default false)

Behavior:

• false: case-insensitive lookup for read/env business keys.
• true: case-sensitive.
• Windows (os.name == "nt"): true is ignored and behaves as false.
• FastAPIEx / FastAPIEx.* lookup is always case-insensitive (independent from CASE_SENSITIVE).
• When false, if sibling keys collapse to the same folded name (for example APP and app), string-path lookup is treated as ambiguous and raises resolve error.

Reload Mode

Control:

• FASTAPIEX__SETTINGS__RELOAD=off|on_change|always (default off)

Behavior:

• off: no auto yaml sync.
• on_change: sync yaml when file state changes.
• always: sync yaml on each read.
• module delta changes still trigger declaration rediscovery/snapshot rebuild.
• runtime controls are resolved from current live snapshot (not direct env re-read).

Intentionally Not Public at Package Root

These capabilities still exist internally, but are not exported from fastapiex.settings:

• manager/registry direct access helpers