pydsettingsforge 1.0.0

Load and merge settings from pyproject.toml and .env files into validated Pydantic models

pydsettingsforge

Load and merge application settings from pyproject.toml and .env files into validated Pydantic models.

Features

• Read settings from pyproject.toml ([project] table + optional [tool.<name>] section)
• Read and merge multiple .env files with explicit priority ordering
• Nested configuration via __ separator in .env keys (e.g., DATABASE__HOST=localhost)
• Automatic coercion of .env list and dict values from Pydantic model hints
• .env values override pyproject.toml values
• Validate merged settings against a user-provided Pydantic model
• Clear, specific error messages for missing files, sections, and validation failures

Installation

uv add pydsettingsforge

Quick Start

1. Define your settings model

from pydantic import BaseModel

class DatabaseConfig(BaseModel):
    host: str
    port: int

class AppSettings(BaseModel):
    name: str
    version: str
    debug: bool = False
    log_level: str = "info"
    database: DatabaseConfig | None = None

2. Add settings to pyproject.toml

[project]
name = "myapp"
version = "1.0.0"

[tool.myapp]
debug = false
log_level = "info"

[tool.myapp.database]
host = "localhost"
port = 5432

3. Create .env files (optional)

# .env
DEBUG=true
LOG_LEVEL=debug

# .env.local (overrides .env)
DATABASE__HOST=db.production.com
DATABASE__PORT=3306

4. Load settings

from pydsettingsforge import load_settings
from myapp.config import AppSettings

settings = load_settings(
    AppSettings,
    tool_section="myapp",
    env_files=[".env", ".env.local"],
)

print(settings.name)            # "myapp"
print(settings.debug)           # True (overridden by .env)
print(settings.database.host)   # "db.production.com" (overridden by .env.local)

Override Priority

Settings are merged in this order (lowest to highest priority):

1. pyproject.toml root section fields (default: [project])
2. pyproject.toml [tool.<name>] section
3. .env files (in the order provided in the env_files list)
4. OS environment variables (if your model inherits from pydantic_settings.BaseSettings)

Lists and Dicts in .env

.env values are always strings, but your Pydantic model knows the target type. pydsettingsforge uses those hints to parse list-like and dict fields automatically:

class AppSettings(BaseModel):
    allowed_hosts: list[str]
    ports: list[int]
    features: dict[str, int]

# .env
ALLOWED_HOSTS=api.example.com,web.example.com
PORTS=80,443,5432
FEATURES={"timeout": 30, "retries": 3}

settings = load_settings(AppSettings, env_files=[".env"])
settings.allowed_hosts  # ["api.example.com", "web.example.com"]
settings.ports          # [80, 443, 5432]  (Pydantic coerces each element)
settings.features       # {"timeout": 30, "retries": 3}

Rules:

• List-like fields (list, set, tuple, frozenset): split on , by default, whitespace stripped, empty parts dropped. If the value starts with [, it is parsed as JSON instead; on invalid JSON the value is split as a fallback.
• Dict fields: parsed as JSON.
• Per-element types (e.g. list[int], list[bool]): the list is split into strings, then Pydantic coerces each element during model validation.
• Optional list/dict fields (list[str] | None) are detected. Multi-member unions like list[str] | int | None also detect the list member.
• Nested model lists (list[BaseModel], set[BaseModel], tuple[BaseModel, ...]): the value must be a JSON list; each element is recursively coerced, so child list / dict fields inside the model are parsed the same way as top-level fields.
• Custom separator: pass list_separator=";" to load_settings to split on a different character.
• Opt out: pass coerce_env=False to keep raw string passthrough (the prior behavior).

If a value cannot be parsed (e.g. malformed JSON for a dict field or a list[BaseModel] field), a SettingsValidationError is raised with the offending field name.

class Server(BaseModel):
    host: str
    tags: list[str]

class AppSettings(BaseModel):
    servers: list[Server]

SERVERS=[{"host": "a.example.com", "tags": "primary,public"}, {"host": "b.example.com", "tags": "backup"}]

settings.servers[0].host  # "a.example.com"
settings.servers[0].tags  # ["primary", "public"]  (child list coerced too)

Custom Root Section

By default, pydsettingsforge reads from the [project] section (filtering to known metadata keys). You can specify a custom root section to read all keys from any TOML table:

[settings]
host = "localhost"
port = 8080
debug = true

settings = load_settings(
    ServerSettings,
    root_section="settings",
)

Extra Fields

By default, Pydantic ignores any fields in your configuration that aren't defined in your model:

class AppSettings(BaseModel):
    debug: bool

# If pyproject.toml has extra fields like "name" or "version",
# they are silently ignored

You can control this behavior using Pydantic's model_config:

Forbid Extra Fields (Strict Mode)

Raise an error if unexpected fields are present:

from pydantic import BaseModel, ConfigDict

class StrictSettings(BaseModel):
    model_config = ConfigDict(extra="forbid")
    debug: bool
    log_level: str

# Raises SettingsValidationError if pyproject.toml contains
# fields not defined in the model

Allow Extra Fields

Accept and store extra fields dynamically:

from pydantic import BaseModel, ConfigDict

class FlexibleSettings(BaseModel):
    model_config = ConfigDict(extra="allow")
    debug: bool

# Extra fields are accessible via settings.model_extra

Note: This behavior is controlled by your Pydantic model configuration, not by pydsettingsforge.

API Reference

load_settings()

def load_settings[T: BaseModel](
    model_class: type[T],
    *,
    pyproject_path: Path | str | None = None,
    env_files: list[Path | str] | None = None,
    tool_section: str | None = None,
    root_section: str = "project",
    env_nesting_separator: str = "__",
    coerce_env: bool = True,
    list_separator: str = ",",
) -> T

Parameter	Type	Default	Description
model_class	type[BaseModel]	required	Pydantic model to validate against
pyproject_path	Path | str | None	./pyproject.toml	Path to pyproject.toml
env_files	list[Path | str] | None	None	Ordered list of .env files (later wins)
tool_section	str | None	None	[tool.<name>] section to read
root_section	str	"project"	Root TOML section to read (custom sections include all keys)
env_nesting_separator	str	"__"	Separator for nested .env keys
coerce_env	bool	True	Parse list/dict string values via the model hints before validation
list_separator	str	","	Separator for list-like fields when coerce_env is enabled

coerce_env_values()

def coerce_env_values(
    model_class: type[BaseModel],
    data: dict[str, Any],
    *,
    list_separator: str = ",",
    coerce_env: bool = True,
) -> dict[str, Any]

The same list/dict coercion that load_settings runs after merging, exposed as a standalone helper. Use it when you build the settings dict yourself (e.g. from a custom config source) and want the same string-to-typed-value behavior before handing the dict to Pydantic.

Parameter	Type	Default	Description
model_class	type[BaseModel]	required	Pydantic model used to interpret each leaf
data	dict[str, Any]	required	The dict to coerce (not mutated)
list_separator	str	","	Separator for list-like fields
coerce_env	bool	True	Set to False to return a shallow copy with no coercion

Exceptions

Exception	When
PyprojectNotFoundError	pyproject.toml not found
EnvFileNotFoundError	A specified .env file doesn't exist
RootSectionNotFoundError	Root section is missing
ToolSectionNotFoundError	[tool.<name>] section is missing
SettingsValidationError	Merged data fails Pydantic validation

Development

Prerequisites

• Python 3.13+
• uv

Setup

git clone <repo-url>
cd pydsettingsforge
uv sync --all-groups

Commands

# Run tests
uv run pytest

# Run tests with coverage
uv run pytest --cov=pydsettingsforge

# Lint
uv run ruff check src/ tests/

# Format
uv run ruff format src/ tests/

# Type check
uv run ty check src/

# All checks
uv run ruff check src/ tests/ && uv run ruff format --check src/ tests/ && uv run ty check src/ && uv run pytest

Project Structure

pydsettingsforge/
├── pyproject.toml
├── uv.lock
├── README.md
├── .gitignore
├── src/
│   └── pydsettingsforge/
│       ├── __init__.py          # Public API: load_settings(), coerce_env_values()
│       ├── constants.py         # Default constants
│       ├── coercer.py           # List/dict coercion from Pydantic hints
│       ├── env_reader.py        # .env file parsing and nesting
│       ├── exceptions.py        # Custom exceptions
│       ├── merger.py            # Deep-merge dictionaries
│       ├── toml_reader.py       # pyproject.toml parsing
│       └── validator.py         # Pydantic validation
└── tests/
    ├── conftest.py              # Shared fixtures
    ├── test_coercer.py
    ├── test_env_reader.py
    ├── test_load_settings.py    # Integration tests
    ├── test_merger.py
    ├── test_toml_reader.py
    └── test_validator.py

License

MIT