interfaces: introduce and use a protocol class for the `charencoding` module
See
f2832de2a46c for details when this was done for the `bdiff` module.
This lets us dump the hack where the `pure` implementation was imported during
the type checking phase to provide signatures for the module methods it
provides. Now the protocol classes are starting to shine, because these methods
are provided by `pure.charencoding` and `cext.parsers`, and references to
`cffi.charencoding` and `cext.charencoding` are forwarded to them as appropriate
by the `policy` module. But none of that matters, as long as the module
returned provides the listed methods.
The interface was copy/pasted from the `pure` module, but `jsonescapeu8fallback`
is omitted because it is accessed from the `pure` module directly when the
escaping fails in the primary module's `jsonescapeu8()`.
[](https://github.com/hukkin/tomli/actions?query=workflow%3ATests+branch%3Amaster+event%3Apush)
[](https://codecov.io/gh/hukkin/tomli)
[](https://pypi.org/project/tomli)
# 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).