idna

• Restore the std3_rules option, which had no effect since changes to UTS #46 processing in Unicode 16. Note that uts46_remap() defaults to enabling STD3 rules, so direct callers will see input containing non-LDH ASCII characters rejected again.
• Performance improvements to UTS #46 mapping, particularly for ASCII-only domains.
• Test on free-threaded CPython with the GIL disabled and document thread safety.
• Expose the Unicode version of the generated tables as idna.unicode_version, and show it in idna --version.
• Add code, text, codepoint and position attributes to IDNAError so that the failed rule and the offending character can be identified without parsing the exception message.
• The deprecated transitional argument to encode() and uts46_remap() is now completely ignored, and gives a deprecation warning for the latter.
• Reject A-labels that are not the canonical Punycode encoding of their U-label.
• Fix CONTEXTJ violations raising IDNAError instead of InvalidCodepointContext.
• Consistently raise IDNAError for empty labels and non-ASCII bytes passed to label helper functions and the incremental codec.
• Add property-based tests, extended fuzzing targets, coverage measurement, and CI checks that the data tables match the generator output.
• Various code quality and tooling improvements.

Thanks to stefan6419846, LouieLuNZ, and Salvatore Corvaglia for contributions to this release.

• When decoding a domain, add a display argument that will pass through invalid labels rather than raising an exception.

• Substantial 75% reduction in memory usage through new data structures and some optimization in processing speed.
• Added a general 1024-character input length cap to the public validation, conversion, and codec entry points. This is well above any legitimate domain or label and guards against pathological inputs.

• Add a command-line interface (python -m idna, also available as the idna script). Encodes or decodes one or more domains supplied as arguments or on standard input, with options to select A-label or U-label output and control error handling.
• Raise the minimum supported Python version to 3.9
• Various code quality improvements

• Enforce DNS-length cap on individual labels early in check_label, short-circuiting contextual-rule processing for oversized input while staying compatible with UTS 46 usage.
• Tidy core helpers: hoist bidi category sets to module-level frozensets (avoiding per-codepoint list construction), simplify length checks, and reuse the shared _unicode_dots_re from idna.core in the codec module.
• Use raise ... from err for proper exception chaining and switch internal string formatting to f-strings.
• Allow flit_core 4.x in the build backend.
• Expand the ruff lint set (flake8-bugbear, flake8-simplify, pyupgrade, perflint) and apply the surfaced fixes; pin lint CI to Python 3.14.
• Add Dependabot configuration for GitHub Actions.
• Convert README and HISTORY from reStructuredText to Markdown.
• Reference CVE-2026-45409 for the 3.14 advisory in place of the initial GHSA identifier.

Thanks to Felix Yan, Stan Ulbrych, and metsw24-max for contributions to this release.

• Removed opportunity to process long inputs into quadratic time by rejecting oversize inputs up-front. Closes a bypass of the CVE-2024-3651 mitigation. [CVE-2026-45409]

Thanks to Stan Ulbrych for reporting the issue.

• Update to Unicode 17.0.0.
• Issue a deprecation warning for the transitional argument.
• Added lazy-loading to provide some performance improvements.
• Removed vestiges of code related to Python 2 support, including segmentation of data structures specific to Jython.

Thanks to Rodrigo Nogueira for contributions to this release.

• Update to Unicode 16.0.0, including significant changes to UTS46 processing. As a result of Unicode ending support for it, transitional processing no longer has an effect and returns the same result.
• Add support for Python 3.14, lowest supported version is Python 3.8.
• Various updates to packaging, including PEP 740 support.

• Reverted to Unicode 15.1.0 data. Unicode 16 has some significant changes to UTS46 processing that will require more work to properly implement.

• Update to Unicode 16.0.0
• Deprecate setup.cfg in favour of pyproject.toml
• Use ruff for code formatting

Thanks to Waket Zheng for contributions to this release.