rustoml

A modern, high-performance TOML library for Python implemented in Rust.

About This Fork

This project is a maintained and enhanced fork of samuelcolvin/rtoml. The original project hasn't been updated in a while, and this fork continues development for the latest Python versions, with additional Rust tooling improvements.

Key Improvements Over Original rtoml

• Python 3.14 Support: Full support for Python 3.14, including free-threaded mode (GIL-free)
• Modern Dependencies: Updated to latest Rust dependencies (PyO3 0.26, toml 0.9)
• Enhanced Error Handling: tomllib-compatible error messages with line/column information
• Comprehensive Docstrings: For improved developer experience and IDE support
• Custom Float Parsing: Support for parse_float parameter (e.g., for Decimal types)
• Binary File Support: Read TOML from binary file handles
• Better Type Safety: Comprehensive type stubs and full mypy strict compatibility
• Modern Tooling: Built with uv, maturin, and modern Python packaging standards

Credits

Original project by Samuel Colvin. This fork maintained by Sean Lees.

Both projects are MIT licensed.

Why Use rustoml

• Correctness: Built on the widely-used and stable toml-rs library. Passes all standard TOML tests with 100% test coverage on Python code.
• Performance: One of the fastest Python TOML libraries available.
• Flexible None handling: Configurable support for None values with custom serialization/deserialization.
• Type safe: Full type annotations with py.typed marker for excellent IDE support and type checking.

Install

Requires python>=3.10, binaries are available from PyPI for Linux, macOS and Windows, see here.

uv add rustoml
# or
pip install rustoml

If no binary is available on PyPI for your system configuration, you'll need Rust stable installed before you can install rustoml.

Usage

load

def load(toml: str | Path | TextIO, *, none_value: str | None = None) -> dict[str, Any]: ...

Parse TOML via a string or file and return a python dictionary.

• toml: a str, Path or file object from open().
• none_value: controlling which value in toml is loaded as None in python. By default, none_value is None, which means nothing is loaded as None

loads

def loads(toml: str, *, none_value: str | None = None) -> dict[str, Any]: ...

Parse a TOML string and return a python dictionary. (provided to match the interface of json and similar libraries)

• toml: a str containing TOML.
• none_value: controlling which value in toml is loaded as None in python. By default, none_value is None, which means nothing is loaded as None

dumps

def dumps(obj: Any, *, pretty: bool = False, none_value: str | None = "null") -> str: ...

Serialize a python object to TOML.

• obj: a python object to be serialized.
• pretty: if True the output has a more "pretty" format.
• none_value: controlling how None values in obj are serialized. none_value=None means None values are ignored.

dump

def dump(
    obj: Any, file: Path | TextIO, *, pretty: bool = False, none_value: str | None = "null"
) -> int: ...

Serialize a python object to TOML and write it to a file.

• obj: a python object to be serialized.
• file: a Path or file object from open().
• pretty: if True the output has a more "pretty" format.
• none_value: controlling how None values in obj are serialized. none_value=None means None values are ignored.

Examples

from datetime import datetime, timezone, timedelta
import rustoml

obj = {
    'title': 'TOML Example',
    'owner': {
        'dob': datetime(1979, 5, 27, 7, 32, tzinfo=timezone(timedelta(hours=-8))),
        'name': 'Tom Preston-Werner',
    },
    'database': {
        'connection_max': 5000,
        'enabled': True,
        'ports': [8001, 8001, 8002],
        'server': '192.168.1.1',
    },
}

loaded_obj = rustoml.load("""\
# This is a TOML document.

title = "TOML Example"

[owner]
name = "Tom Preston-Werner"
dob = 1979-05-27T07:32:00-08:00 # First class dates

[database]
server = "192.168.1.1"
ports = [8001, 8001, 8002]
connection_max = 5000
enabled = true
""")

assert loaded_obj == obj

assert rustoml.dumps(obj) == """\
title = "TOML Example"

[owner]
dob = 1979-05-27T07:32:00-08:00
name = "Tom Preston-Werner"

[database]
connection_max = 5000
enabled = true
server = "192.168.1.1"
ports = [8001, 8001, 8002]
"""

An example of None-value handling:

obj = {
    'a': None,
    'b': 1,
    'c': [1, 2, None, 3],
}

# Ignore None values
assert rustoml.dumps(obj, none_value=None) == """\
b = 1
c = [1, 2, 3]
"""

# Serialize None values as '@None'
assert rustoml.dumps(obj, none_value='@None') == """\
a = "@None"
b = 1
c = [1, 2, "@None", 3]
"""

# Deserialize '@None' back to None
assert rustoml.load("""\
a = "@None"
b = 1
c = [1, 2, "@None", 3]
""", none_value='@None') == obj