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A lil' TOML parser

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A lil' TOML parser

Tomli is a Python library for parsing TOML. Tomli is fully compatible with TOML v1.0.0.


pip install tomli


Parse a TOML string

import tomli

toml_str = """
gretzky = 99

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", encoding="utf-8") as f:
    toml_dict = tomli.load(f)

Handle invalid TOML

import tomli

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

Construct decimal.Decimals from TOML floats

from decimal import Decimal
import tomli

toml_dict = tomli.loads("precision-matters = 0.982492", parse_float=Decimal)
assert isinstance(toml_dict["precision-matters"], Decimal)


Why this parser?

  • it's lil'
  • pure Python with zero dependencies
  • fairly fast (but pure Python so can't do any miracles there)
  • 100% spec compliance: passes all tests in a test set soon to be merged to the official compliance tests for TOML repository
  • 100% test 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 (list, int, str, datetime.datetime etc.). Preserving comments requires a custom type to be returned so will not be supported, at least not by the tomli.loads function.

Is there a dumps, write or encode function?

Not yet, and it's possible there never will be.


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. On May 28 2021 running the benchmark output the following on my notebook computer.

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==0.6.1,toml==0.10.2,tomli==0.2.0,tomlkit==0.7.2
benchmark-pypi run-test-pre: PYTHONHASHSEED='305387179'
benchmark-pypi run-test: commands[0] | python benchmark/
Parsing data.toml 5000 times:
    parser |  exec time | performance (more is better)
  pytomlpp |     1.16 s | baseline
     rtoml |     1.17 s | 1x baseline
     tomli |     8.94 s | 0.13x baseline
      toml |     9.33 s | 0.12x baseline
     qtoml |     15.7 s | 0.074x baseline
   tomlkit |       70 s | 0.017x baseline

The parsers are ordered from fastest to slowest, using the fastest parser (pytomlpp) as baseline. Tomli performed the best out of all pure Python TOML parsers, losing only to pytomlpp (wraps C++) and rtoml (wraps Rust).

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