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# Tomli

> A lil' TOML parser

**Table of Contents**  *generated with [mdformat-toc](https://github.com/hukkin/mdformat-toc)*

<!-- mdformat-toc start --slug=github --maxlevel=6 --minlevel=2 -->

- [Intro](#intro)

- [Installation](#installation)

- [Usage](#usage)

  - [Parse a TOML string](#parse-a-toml-string)

  - [Parse a TOML file](#parse-a-toml-file)

  - [Handle invalid TOML](#handle-invalid-toml)

  - [Construct `decimal.Decimal`s from TOML floats](#construct-decimaldecimals-from-toml-floats)

- [FAQ](#faq)

  - [Why this parser?](#why-this-parser)

  - [Is comment preserving round-trip parsing supported?](#is-comment-preserving-round-trip-parsing-supported)

  - [Is there a `dumps`, `write` or `encode` function?](#is-there-a-dumps-write-or-encode-function)

  - [How do TOML types map into Python types?](#how-do-toml-types-map-into-python-types)

- [Performance](#performance)

<!-- mdformat-toc end -->

## Intro<a name="intro"></a>

Tomli is a Python library for parsing [TOML](https://toml.io).

Tomli is fully compatible with [TOML v1.0.0](https://toml.io/en/v1.0.0).

## Installation<a name="installation"></a>

```bash

pip install tomli

```

## Usage<a name="usage"></a>

### Parse a TOML string<a name="parse-a-toml-string"></a>

```python

import tomli

toml_str = """

           gretzky = 99

           [kurri]

           jari = 17

           """

toml_dict = tomli.loads(toml_str)

assert toml_dict == {"gretzky": 99, "kurri": {"jari": 17}}

```

### Parse a TOML file<a name="parse-a-toml-file"></a>

```python

import tomli

with open("path_to_file/conf.toml", "rb") as f:

    toml_dict = tomli.load(f)

```

The file must be opened in binary mode (with the `"rb"` flag).

Binary mode will enforce decoding the file as UTF-8 with universal newlines disabled,

both of which are required to correctly parse TOML.

Support for text file objects is deprecated for removal in the next major release.

### Handle invalid TOML<a name="handle-invalid-toml"></a>

```python

import tomli

try:

    toml_dict = tomli.loads("]] this is invalid TOML [[")

except tomli.TOMLDecodeError:

    print("Yep, definitely not valid.")

```

Note that while the `TOMLDecodeError` type is public API, error messages of raised instances of it are not.

Error messages should not be assumed to stay constant across Tomli versions.

### Construct `decimal.Decimal`s from TOML floats<a name="construct-decimaldecimals-from-toml-floats"></a>

```python

from decimal import Decimal

import tomli

toml_dict = tomli.loads("precision-matters = 0.982492", parse_float=Decimal)

assert toml_dict["precision-matters"] == Decimal("0.982492")

```

Note that `decimal.Decimal` can be replaced with another callable that converts a TOML float from string to a Python type.

The `decimal.Decimal` is, however, a practical choice for use cases where float inaccuracies can not be tolerated.

Illegal types include `dict`, `list`, and anything that has the `append` attribute.

Parsing floats into an illegal type results in undefined behavior.

## FAQ<a name="faq"></a>

### Why this parser?<a name="why-this-parser"></a>

- it's lil'

- pure Python with zero dependencies

- the fastest pure Python parser [\*](#performance):

  15x as fast as [tomlkit](https://pypi.org/project/tomlkit/),

  2.4x as fast as [toml](https://pypi.org/project/toml/)

- outputs [basic data types](#how-do-toml-types-map-into-python-types) only

- 100% spec compliant: passes all tests in

  [a test set](https://github.com/toml-lang/compliance/pull/8)

  soon to be merged to the official

  [compliance tests for TOML](https://github.com/toml-lang/compliance)

  repository

- thoroughly tested: 100% branch coverage

### Is comment preserving round-trip parsing supported?<a name="is-comment-preserving-round-trip-parsing-supported"></a>

No.

The `tomli.loads` function returns a plain `dict` that is populated with builtin types and types from the standard library only.

Preserving comments requires a custom type to be returned so will not be supported,

at least not by the `tomli.loads` and `tomli.load` functions.

Look into [TOML Kit](https://github.com/sdispater/tomlkit) if preservation of style is what you need.

### Is there a `dumps`, `write` or `encode` function?<a name="is-there-a-dumps-write-or-encode-function"></a>

[Tomli-W](https://github.com/hukkin/tomli-w) is the write-only counterpart of Tomli, providing `dump` and `dumps` functions.

The core library does not include write capability, as most TOML use cases are read-only, and Tomli intends to be minimal.

### How do TOML types map into Python types?<a name="how-do-toml-types-map-into-python-types"></a>

| TOML type        | Python type         | Details                                                      |

| ---------------- | ------------------- | ------------------------------------------------------------ |

| Document Root    | `dict`              |                                                              |

| Key              | `str`               |                                                              |

| String           | `str`               |                                                              |

| Integer          | `int`               |                                                              |

| Float            | `float`             |                                                              |

| Boolean          | `bool`              |                                                              |

| Offset Date-Time | `datetime.datetime` | `tzinfo` attribute set to an instance of `datetime.timezone` |

| Local Date-Time  | `datetime.datetime` | `tzinfo` attribute set to `None`                             |

| Local Date       | `datetime.date`     |                                                              |

| Local Time       | `datetime.time`     |                                                              |

| Array            | `list`              |                                                              |

| Table            | `dict`              |                                                              |

| Inline Table     | `dict`              |                                                              |

## Performance<a name="performance"></a>

The `benchmark/` folder in this repository contains a performance benchmark for comparing the various Python TOML parsers.

The benchmark can be run with `tox -e benchmark-pypi`.

Running the benchmark on my personal computer output the following:

```console

foo@bar:~/dev/tomli$ tox -e benchmark-pypi

benchmark-pypi installed: attrs==19.3.0,click==7.1.2,pytomlpp==1.0.2,qtoml==0.3.0,rtoml==0.7.0,toml==0.10.2,tomli==1.1.0,tomlkit==0.7.2

benchmark-pypi run-test-pre: PYTHONHASHSEED='2658546909'

benchmark-pypi run-test: commands[0] | python -c 'import datetime; print(datetime.date.today())'

2021-07-23

benchmark-pypi run-test: commands[1] | python --version

Python 3.8.10

benchmark-pypi run-test: commands[2] | python benchmark/run.py

Parsing data.toml 5000 times:

------------------------------------------------------

    parser |  exec time | performance (more is better)

-----------+------------+-----------------------------

     rtoml |    0.901 s | baseline (100%)

  pytomlpp |     1.08 s | 83.15%

     tomli |     3.89 s | 23.15%

      toml |     9.36 s | 9.63%

     qtoml |     11.5 s | 7.82%

   tomlkit |     56.8 s | 1.59%

```

The parsers are ordered from fastest to slowest, using the fastest parser as baseline.

Tomli performed the best out of all pure Python TOML parsers,

losing only to pytomlpp (wraps C++) and rtoml (wraps Rust).