Changelog

To be included in v6.6.3 (if present)

Released versions

6.6.3

(2025-06-30)

Bug fixes

  • Fixed inconsistencies generated by the C implementation of _md_shrink() which might later lead to assertion failures and crash – by @Romain-Geissler-1A.

    Related issues and pull requests on GitHub: #1229.


6.6.2

(2025-06-28)

Bug fixes

  • Fixed a memory corruption issue in the C implementation of _md_shrink() that could lead to segmentation faults and data loss when items were deleted from a MultiDict. The issue was an edge case in the pointer arithmetic during the compaction phase – by @bdraco.

    Related issues and pull requests on GitHub: #1221, #1222.

  • Fixed format string compilation errors in debug builds on 32-bit platforms by using portable %zd format specifiers for Py_ssize_t values instead of %ld – by @bdraco.

    Related issues and pull requests on GitHub: #1225, #1226.

Packaging updates and notes for downstreams

  • Re-enabled 32-bit Linux wheel builds that were disabled by default in cibuildwheel 3.0.0 – by @bdraco.

    Related issues and pull requests on GitHub: #1225, #1227.


6.6.1

(2025-06-28)

Bug fixes

Contributor-facing changes

  • Fixed setuptools deprecation warning about the license specification – by @asvetlov.

    Related issues and pull requests on GitHub: #1216.

  • Fix compiler warnings and convert them to errors – by @asvetlov.

    Related issues and pull requests on GitHub: #1217.


6.6.0

(2025-06-27)

Features

  • Added multidict.MultiDict.merge() which copies all items from arguments if its key not exist in the dictionary – by @asvetlov.

    Related issues and pull requests on GitHub: #292.

  • Stopped reallocating memory for the internal htkeys_t structure when inserting new items if the multidict has deleted items and it could be collapsed in-place. Removal of malloc()/free() improves the performance slightly.

    The change affects C implementation only, pure Python code is not changed.

    Patch by @asvetlov.

    Related issues and pull requests on GitHub: #1200.

  • C implementation of multidict.MultiDict.getall now is slightly faster if it returns nothing – by @asvetlov.

    Related issues and pull requests on GitHub: #1212.

Improved documentation

Contributor-facing changes

  • When building wheels, the source distribution is now passed directly to the cibuildwheel invocation – by @webknjaz.

    Related issues and pull requests on GitHub: #1199.

  • Set up PYTHONHASHSEED for benchmarks execution to make measured times stable – by @asvetlov.

    Related issues and pull requests on GitHub: #1202.


6.5.1

(2025-06-24)

Bug fixes

  • Fixed a bug in C implementation when multidict is resized and it has deleted slots.

    The bug was introduced by multidict 6.5.0 release.

    Patch by @asvetlov.

    Related issues and pull requests on GitHub: #1195.

Contributor-facing changes

  • A pair of code formatters for Python and C have been configured in the pre-commit tool.

    Related issues and pull requests on GitHub: #1123.

  • Shorted fixture parametrization ids.

    For example, test_keys_view_xor[case-insensitive-pure-python-module] becomes test_keys_view_xor[ci-py] – by @asvetlov.

    Related issues and pull requests on GitHub: #1192.

  • The reusable-cibuildwheel.yml workflow has been refactored to be more generic and ci-cd.yml now holds all the configuration toggles – by @webknjaz.

    Related issues and pull requests on GitHub: #1193.


6.5.0

(2025-06-17)

Note

The release was yanked because of #1195, multidict 6.5.1 should be used instead.

Features

  • Replace internal implementation from an array of items to hash table. algorithmic complexity for lookups is switched from O(N) to O(1).

    The hash table is very similar to dict from CPython but it allows keys duplication.

    The benchmark shows 25-50% boost for single lookups, x2-x3 for bulk updates, and x20 for some multidict view operations. The gain is not for free: add and extend are 25-50% slower now. We consider it as acceptable because the lookup is much more common operation that addition for the library domain.

    Related issues and pull requests on GitHub: #1128.

Contributor-facing changes

  • Builds have been added for arm64 Windows wheels and the reusable-build-wheel.yml template has been modified to allow for an os value (windows-11-arm) which does not end with the -latest postfix.

    Related issues and pull requests on GitHub: #1167.


6.4.4

(2025-05-19)

Bug fixes

Miscellaneous internal changes

  • multidict.MultiDictProxy was refactored to rely only on multidict.MultiDict public interface and don’t touch any implementation details.

    Related issues and pull requests on GitHub: #1150.

  • Multidict views were refactored to rely only on multidict.MultiDict API and don’t touch any implementation details.

    Related issues and pull requests on GitHub: #1152.

  • Dropped internal _Impl class from pure Python implementation, both pure Python and C Extension follows the same design internally now.

    Related issues and pull requests on GitHub: #1153.


6.4.3

(2025-04-10)

Bug fixes

  • Fixed building the library in debug mode.

    Related issues and pull requests on GitHub: #1144.

  • Fixed custom PyType_GetModuleByDef() when non-heap type object was passed.

    Related issues and pull requests on GitHub: #1147.

Packaging updates and notes for downstreams


6.4.2

(2025-04-09)

Bug fixes

  • Fixed a segmentation fault when creating subclassed MultiDict objects on Python < 3.11 – by @bdraco.

    The problem first appeared in 6.4.0

    Related issues and pull requests on GitHub: #1141.


6.4.1

(2025-04-09)

No significant changes.


6.4.0

(2025-04-09)

Bug fixes

  • Fixed a memory leak creating new istr objects – by @bdraco.

    The leak was introduced in 6.3.0

    Related issues and pull requests on GitHub: #1133.

  • Fixed reference counting when calling multidict.MultiDict.update() – by @bdraco.

    The leak was introduced in 4.4.0

    Related issues and pull requests on GitHub: #1135.

Features

  • Switched C Extension to use heap types and the module state.

    Related issues and pull requests on GitHub: #1125.

  • Started building armv7l wheels – by @bdraco.

    Related issues and pull requests on GitHub: #1127.


6.3.2

(2025-04-03)

Bug fixes

  • Resolved a memory leak by ensuring proper reference count decrementation – by @asvetlov and @bdraco.

    Related issues and pull requests on GitHub: #1121.


6.3.1

(2025-04-01)

Bug fixes

  • Fixed keys not becoming case-insensitive when multidict.CIMultiDict is created by passing in a multidict.MultiDict – by @bdraco.

    Related issues and pull requests on GitHub: #1112.

  • Fixed the pure Python version mutating the original multidict.MultiDict when creating a new multidict.CIMultiDict from an existing one when keyword arguments are also passed – by @bdraco.

    Related issues and pull requests on GitHub: #1113.

  • Prevented crashing with a segfault when repr() is called for recursive multidicts and their proxies and views.

    Related issues and pull requests on GitHub: #1115.


6.3.0

(2025-03-31)

Bug fixes

  • Set operations for KeysView and ItemsView of case-insensitive multidicts and their proxies are processed in case-insensitive manner.

    Related issues and pull requests on GitHub: #965.

  • Rewrote multidict.CIMultiDict and it proxy to always return multidict.istr keys. istr is derived from str, thus the change is backward compatible.

    The performance boost is about 15% for some operations for C Extension, pure Python implementation have got a visible (15% - 230%) speedup as well.

    Related issues and pull requests on GitHub: #1097.

  • Fixed a crash when extending a multidict from multidict proxy if C Extensions were used.

    Related issues and pull requests on GitHub: #1100.

Features

  • Implemented a custom parser for METH_FASTCALL | METH_KEYWORDS protocol – by @asvetlov.

    The patch re-enables fast call protocol in the multidict C Extension.

    Speedup is about 25%-30% for the library benchmarks for Python 3.12+.

    Related issues and pull requests on GitHub: #1070.

  • The C-extension no longer pre-allocates a Python exception object in lookup-related methods of MultiDict when the passed-in key is not found but default value is provided.

    Namely, this affects MultiDict.getone(), MultiDict.getall(), MultiDict.get(), MultiDict.pop(), MultiDict.popone(), and MultiDict.popall().

    Additionally, the MultiDict comparison with regular dictionaries is now about 60% faster on Python 3.13+ in the fallback-to-default case.

    Related issues and pull requests on GitHub: #1078.

  • Implemented __repr__() for C Extension classes in C.

    The speedup is about 2.5 times.

    Related issues and pull requests on GitHub: #1081.

  • Made C version of multidict.istr pickleable.

    Related issues and pull requests on GitHub: #1098.

  • Optimized multidict creation and extending / updating if C Extensions are used.

    The speedup is between 25% and 70% depending on the usage scenario.

    Related issues and pull requests on GitHub: #1101.

  • multidict.MultiDict.popitem() is changed to remove the latest entry instead of the first.

    It gives O(1) amortized complexity.

    The standard dict.popitem() removes the last entry also.

    Related issues and pull requests on GitHub: #1105.

Contributor-facing changes

  • Started running benchmarks for the pure Python implementation in addition to the C implementation – by @bdraco.

    Related issues and pull requests on GitHub: #1092.

  • The the project-wide Codecov metric is no longer reported via GitHub Checks API. The combined value is not very useful because one of the sources (MyPy) cannot reach 100% with the current state of the ecosystem. We may want to reconsider in the future. Instead, we now have two separate “runtime coverage” metrics for library code and tests. They are to be kept at 100% at all times. And the “type coverage” metric will remain advisory, at a lower threshold.

    The default patch metric check is renamed to “runtime” to better reflect its semantics. This one will also require 100% coverage. Another “typing” patch coverage metric is now reported alongside it. It’s considered advisory, just like its project counterpart.

    When looking at Codecov, one will likely want to look at MyPy and pytest flags separately. It is usually best to avoid looking at the PR pages that sometimes display combined coverage incorrectly.

    The change additionally disables the deprecated GitHub Annotations integration in Codecov.

    Finally, the badge coloring range now starts at 100%.

    Coverage metrics

    – by @webknjaz

    Related issues and pull requests on GitHub: #1093.

Miscellaneous internal changes

  • Synchronized pythoncapi_compat.h with the latest available version.

    Related issues and pull requests on GitHub: #1063.

  • Moved registering ABCs for C Extension classes from C to Python.

    Related issues and pull requests on GitHub: #1083.

  • Refactored the internal pair_list implementation.

    Related issues and pull requests on GitHub: #1084.

  • Implemented views comparison and disjoints in C instead of Python helpers.

    The performance boost is about 40%.

    Related issues and pull requests on GitHub: #1096.


6.2.0

(2025-03-17)

Bug fixes

  • Fixed in checks throwing an exception instead of returning False when testing non-strings.

    Related issues and pull requests on GitHub: #1045.

  • Fixed a leak when the last accessed module in PyInit__multidict() init is not released.

    Related issues and pull requests on GitHub: #1061.

Features

  • Implemented support for the free-threaded build of CPython 3.13 – by @lysnikolaou.

    Related issues and pull requests on GitHub: #1015.

Packaging updates and notes for downstreams

  • Started publishing wheels made for the free-threaded build of CPython 3.13 – by @lysnikolaou.

    Related issues and pull requests on GitHub: #1015.

Miscellaneous internal changes

  • Used stricter typing across the code base, resulting in improved typing accuracy across multidict classes. Funded by an NLnet grant.

    Related issues and pull requests on GitHub: #1046.


6.1.0 (2024-09-09)

Bug fixes

  • Covered the unreachable code path in multidict._multidict_base._abc_itemsview_register() with typing – by @skinnyBat.

    Related issues and pull requests on GitHub: #928.

Features

  • Added support for Python 3.13 – by @bdraco.

    Related issues and pull requests on GitHub: #1002.

Removals and backward incompatible breaking changes

  • Removed Python 3.7 support – by @bdraco.

    Related issues and pull requests on GitHub: #997.

Contributor-facing changes

  • Added tests to have full code coverage of the multidict._multidict_base._viewbaseset_richcmp() function – by @skinnyBat.

    Related issues and pull requests on GitHub: #928.

  • The deprecated ::set-output workflow command has been replaced by the $GITHUB_OUTPUT environment variable in the GitHub Actions CI/CD workflow definition.

    Related issues and pull requests on GitHub: #940.

  • codecov-action has been temporarily downgraded to v3 in the GitHub Actions CI/CD workflow definitions in order to fix uploading coverage to Codecov. See this issue for more details.

    Related issues and pull requests on GitHub: #941.

  • In the GitHub Actions CI/CD workflow definition, the Get pip cache dir step has been fixed for Windows runners by adding shell: bash. See actions/runner#2224 for more details.

    Related issues and pull requests on GitHub: #942.

  • Interpolation of the pip cache keys has been fixed by adding missing $ syntax in the GitHub Actions CI/CD workflow definition.

    Related issues and pull requests on GitHub: #943.


6.0.5 (2024-02-01)

Bug fixes

  • Upgraded the C-API macros that have been deprecated in Python 3.9 and later removed in 3.13 – by @iemelyanov.

    Related issues and pull requests on GitHub: #862, #864, #868, #898.

  • Reverted to using the public argument parsing API PyArg_ParseTupleAndKeywords() under Python 3.12 – by @charles-dyfis-net and @webknjaz.

    The effect is that this change prevents build failures with clang 16.9.6 and gcc-14 reported in #926. It also fixes a segmentation fault crash caused by passing keyword arguments to MultiDict.getall() discovered by @jonaslb and @hroncok while examining the problem.

    Related issues and pull requests on GitHub: #862, #909, #926, #929.

  • Fixed a SystemError: null argument to internal routine error on a MultiDict.items().isdisjoint() call when using C Extensions.

    Related issues and pull requests on GitHub: #927.

Improved documentation

  • On the Contributing docs page, a link to the Towncrier philosophy has been fixed.

    Related issues and pull requests on GitHub: #911.

Packaging updates and notes for downstreams

  • Stopped marking all files as installable package data – by @webknjaz.

    This change helps setuptools understand that C-headers are not to be installed under lib/python3.x/site-packages/.

    Related commits on GitHub: 31e1170.

  • Started publishing pure-python wheels to be installed as a fallback – by @webknjaz.

    Related commits on GitHub: 7ba0e72.

  • Switched from setuptools’ legacy backend (setuptools.build_meta:__legacy__) to the modern one (setuptools.build_meta) by actually specifying the the [build-system] build-backend option in pyproject.toml – by @Jackenmen.

    Related issues and pull requests on GitHub: #802.

  • Declared Python 3.12 supported officially in the distribution package metadata – by @hugovk.

    Related issues and pull requests on GitHub: #877.

Contributor-facing changes

  • The test framework has been refactored. In the previous state, the circular imports reported in #837 caused the C-extension tests to be skipped.

    Now, there is a set of the pytest fixtures that is set up in a parametrized manner allowing to have a consistent way of accessing mirrored multidict implementations across all the tests.

    This change also implemented a pair of CLI flags (--c-extensions / --no-c-extensions) that allow to explicitly request deselecting the tests running against the C-extension.

    – by @webknjaz.

    Related issues and pull requests on GitHub: #98, #837, #915.

  • Updated the test pins lockfile used in the cibuildwheel test stage – by @hoodmane.

    Related issues and pull requests on GitHub: #827.

  • Added an explicit void for arguments in C-function signatures which addresses the following compiler warning:

    warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
    

    – by @hoodmane

    Related issues and pull requests on GitHub: #828.

  • An experimental Python 3.13 job now runs in the CI – @webknjaz.

    Related issues and pull requests on GitHub: #920.

  • Added test coverage for the and, or, sub, and xor operators in the multidict/_multidict_base.py module. It also covers NotImplemented and “Iterable-but-not-Set” cases there.

    – by @a5r0n

    Related issues and pull requests on GitHub: #936.

  • The version of pytest is now capped below 8, when running MyPy against Python 3.7. This pytest release dropped support for said runtime.

    Related issues and pull requests on GitHub: #937.


6.0.4 (2022-12-24)

Bugfixes

  • Fixed a type annotations regression introduced in v6.0.2 under Python versions <3.10. It was caused by importing certain types only available in newer versions. (#798)

6.0.3 (2022-12-03)

Features

  • Declared the official support for Python 3.11 — by @mlegner. (#872)

6.0.2 (2022-01-24)

Bugfixes

  • Revert #644, restore type annotations to as-of 5.2.0 version. (#688)

6.0.1 (2022-01-23)

Bugfixes

  • Restored back MultiDict, CIMultiDict, MultiDictProxy, and CIMutiDictProxy generic type arguments; they are parameterized by value type, but the key type is fixed by container class.

    MultiDict[int] means MutableMultiMapping[str, int]. The key type of MultiDict is always str, while all str-like keys are accepted by API and converted to str internally.

    The same is true for CIMultiDict[int] which means MutableMultiMapping[istr, int]. str-like keys are accepted but converted to istr internally. (#682)

6.0.0 (2022-01-22)

Features

  • Use METH_FASTCALL where it makes sense.

    MultiDict.add() is 2.2 times faster now, CIMultiDict.add() is 1.5 times faster. The same boost is applied to get*(), setdefault(), and pop*() methods. (#681)

Bugfixes

  • Fixed type annotations for keys of multidict mapping classes. (#644)

  • Support Multidict[int] for pure-python version. __class_getitem__ is already provided by C Extension, making it work with the pure-extension too. (#678)

Deprecations and Removals

  • Dropped Python 3.6 support (#680)

Misc

5.2.0 (2021-10-03)

Features

    1. Added support Python 3.10

    2. Started shipping platform-specific wheels with the musl tag targeting typical Alpine Linux runtimes.

    3. Started shipping platform-specific arm64 wheels for Apple Silicon. (#629)

Bugfixes

  • Fixed pure-python implementation that used to raise “Dictionary changed during iteration” error when iterated view (.keys(), .values() or .items()) was created before the dictionary’s content change. (#620)

5.1.0 (2020-12-03)

Features

  • Supported GenericAliases (MultiDict[str]) for Python 3.9+ #553

Bugfixes

  • Synchronized the declared supported Python versions in setup.py with actually supported and tested ones. #552


5.0.1 (2020-11-14)

Bugfixes

  • Provided x86 Windows wheels #550


5.0.0 (2020-10-12)

Features

  • Provided wheels for aarch64, i686, ppc64le, s390x architectures on Linux as well as x86_64. #500

  • Provided wheels for Python 3.9. #534

Removal

  • Dropped Python 3.5 support; Python 3.6 is the minimal supported Python version.

Misc