tomli 2.0.1

Description:

tomli 2.0.1

Tomli

A lil' TOML parser

Table of Contents generated with mdformat-toc


Intro
Installation
Usage

Parse a TOML string
Parse a TOML file
Handle invalid TOML
Construct decimal.Decimals from TOML floats


FAQ

Why this parser?
Is comment preserving round-trip parsing supported?
Is there a dumps, write or encode function?
How do TOML types map into Python types?


Performance


Intro
Tomli is a Python library for parsing TOML.
Tomli is fully compatible with TOML v1.0.0.
Installation
pip install tomli

Usage
Parse a TOML string
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
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.
Handle invalid TOML
import tomli

try:
toml_dict = tomli.loads("]] this is invalid TOML [[")
except tomli.TOMLDecodeError:
print("Yep, definitely not valid.")

Note that error messages are considered informational only.
They should not be assumed to stay constant across Tomli versions.
Construct decimal.Decimals from TOML floats
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 are dict and list, and their subtypes.
A ValueError will be raised if parse_float produces illegal types.
FAQ
Why this parser?

it's lil'
pure Python with zero dependencies
the fastest pure Python parser *:
15x as fast as tomlkit,
2.4x as fast as toml
outputs basic data types only
100% spec compliant: passes all tests in
a test set
soon to be merged to the official
compliance tests for TOML
repository
thoroughly tested: 100% branch coverage

Is comment preserving round-trip parsing supported?
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 if preservation of style is what you need.
Is there a dumps, write or encode function?
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?



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
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:
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).