tomllib — Parse TOML files

Source code: Lib/tomllib

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This module provides an interface for parsing TOML 1.1.0 (Tom’s Obvious Minimal Language, https://toml.io). This module does not support writing TOML.

Added in version 3.11: The module was added with support for TOML 1.0.0.

Changed in version 3.15: Added TOML 1.1.0 support. See the What’s New for details.

Warning

Be cautious when parsing data from untrusted sources. A malicious TOML string may cause the decoder to consume considerable CPU and memory resources. Limiting the size of data to be parsed is recommended.

See also

The Tomli-W package is a TOML writer that can be used in conjunction with this module, providing a write API familiar to users of the standard library marshal and pickle modules.

See also

The TOML Kit package is a style-preserving TOML library with both read and write capability. It is a recommended replacement for this module for editing already existing TOML files.

This module defines the following functions:

tomllib.load(fp, /, *, parse_float=float)

Read a TOML file. The first argument should be a readable and binary file object. Return a dict. Convert TOML types to Python using this conversion table.

parse_float will be called with the string of every TOML float to be decoded. By default, this is equivalent to float(num_str). This can be used to use another datatype or parser for TOML floats (e.g. decimal.Decimal). The callable must not return a dict or a list, else a ValueError is raised.

A TOMLDecodeError will be raised on an invalid TOML document.

tomllib.loads(s, /, *, parse_float=float)

Load TOML from a str object. Return a dict. Convert TOML types to Python using this conversion table. The parse_float argument has the same meaning as in load().

A TOMLDecodeError will be raised on an invalid TOML document.

The following exceptions are available:

exception tomllib.TOMLDecodeError(msg, doc, pos)

Subclass of ValueError with the following additional attributes:

msg

The unformatted error message.

doc

The TOML document being parsed.

pos

The index of doc where parsing failed.

lineno

The line corresponding to pos.

colno

The column corresponding to pos.

Changed in version 3.14: Added the msg, doc and pos parameters. Added the msg, doc, pos, lineno and colno attributes.

Deprecated since version 3.14: Passing free-form positional arguments is deprecated.

Examples

Parsing a TOML file:

import tomllib

with open("pyproject.toml", "rb") as f:
    data = tomllib.load(f)

Parsing a TOML string:

import tomllib

toml_str = """
python-version = "3.11.0"
python-implementation = "CPython"
"""

data = tomllib.loads(toml_str)

Conversion Table

TOML	Python
TOML document	dict
string	str
integer	int
float	float (configurable with parse_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
array of tables	list of dicts

Limits and interoperability considerations

tomllib places some limits on the documents it can handle, and it preserves details that other TOML parsers are allowed to ignore. When writing portable TOML files, consider only using features that are guaranteed or recommended by the standard.

The implementation details listed here may change in future versions of Python.

Tables/dicts

Key/value pairs in TOML documents and tables are not guaranteed to be in any specific order.

CPython implementation detail: tomllib loads dictionary entries in the order they appear in the source.

Integers

TOML recommends supporting integers in range(−2**63, 2**63).

CPython implementation detail: tomllib uses Python’s limit on integer string conversion (4300 digits by default).

Floats

TOML recommends supporting at least IEEE 754 binary64 values, which means that numbers with more than 15 significant decimal digits are likely to be rounded.

CPython implementation detail: tomllib uses Python float by default; on many common platforms this is the recommended binary64. See sys.float_info for details.

Nesting limit

TOML 1.1.0 does not recommend a limit on how deeply arrays and tables may be nested inside one another. (A limit of 100 has been proposed for a future version of TOML.)

CPython implementation detail: In tomllib, the nesting level is mainly limited by Python’s recursion limit. Note that code that calls tomllib may contribute to the limit.