gh-141510, PEP 814: Add built-in frozendict type by vstinner · Pull Request #144757 · python/cpython

vstinner · 2026-02-12T18:21:35Z

Add TYPE_FROZENDICT to the marshal module.

Add C API functions:

PyAnyDict_Check()
PyAnyDict_CheckExact()
PyFrozenDict_Check()
PyFrozenDict_CheckExact()
PyFrozenDict_New()

Add PyFrozenDict_Type C type.

Issue: PEP 814: Add built-in frozendict type #141510

📚 Documentation preview 📚: https://cpython-previews--144757.org.readthedocs.build/en/144757/c-api/dict.html#frozen-dictionary-objects

Add TYPE_FROZENDICT to the marshal module. Add C API functions: * PyAnyDict_Check() * PyAnyDict_CheckExact() * PyFrozenDict_Check() * PyFrozenDict_CheckExact() * PyFrozenDict_New() Add PyFrozenDict_Type C type.

vstinner · 2026-02-13T07:49:35Z

cc @corona10

Fix also indentation.

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

corona10 · 2026-02-13T13:00:43Z

 }

- if (PyDict_CheckExact(d)) {
+ if (PyAnyDict_CheckExact(d)) {


Maybe same opinion with @kumaraditya303 we can avoid a lot of critical section if dict is frozen dict.

I agree, but I would prefer to make such "optimization" change in a separated PR.

corona10 · 2026-02-13T13:01:28Z

 dict_length(PyObject *self)
 {
- return FT_ATOMIC_LOAD_SSIZE_RELAXED(((PyDictObject *)self)->ma_used);
+ return GET_USED(_PyAnyDict_CAST(self));


Do we have to use atomic operation for frozendict?

No, we can skip the atomic operation for frozendict.

It uses relaxed atomic so it compiles to simple loads so avoiding it has no real benefit.

len(frozendict) has been optimized by #144913.

corona10 · 2026-02-13T13:02:04Z

+};
+
+static PyMappingMethods frozendict_as_mapping = {
+ .mp_length = dict_length,


I think that we can make frozendict_lenth

I propose to make such optimization in a separated PR.

corona10 · 2026-02-13T13:05:55Z

+
+static PyMappingMethods frozendict_as_mapping = {
+ .mp_length = dict_length,
+ .mp_subscript = dict_subscript,


Still perfer to make frozendict_subscript, but let's do it at the separate PR.

corona10

We should notice that frozendict is not subclass of dict to follow SC feedback

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Document frozendict after lazy import.

vstinner · 2026-02-13T15:02:44Z

 mp->ma_values == NULL &&
- (mp->ma_used >= (mp->ma_keys->dk_nentries * 2) / 3))
+ (mp->ma_used >= (mp->ma_keys->dk_nentries * 2) / 3) &&
+ !frozendict)


We might take this fast-path for frozendict as well. It's just a missed optimization opportunity.
@corona10: Add it to the optimization TODO list :-)

Yeah I will take a look at it

vstinner · 2026-02-13T15:07:01Z

+ if (items == NULL) {
+ return -1;
+ }
+ PyObject *frozenset = PyFrozenSet_New(items);


The current implementation creates an actual frozenset object which emits surprising error messages:
>>> hash(frozendict(x=[])) Traceback (most recent call last): File "<python-input-0>", line 1, in <module> hash(frozendict(x=[])) ~~~~^^^^^^^^^^^^^^^^^^ TypeError: cannot use 'tuple' as a set element (unhashable type: 'list')
We may change the implementation later to not create an actual frozenset, but reuse frozenset hash code instead, to avoid the surprising errors.

I changed the implementation in #144919.

vstinner · 2026-02-13T15:13:01Z

We should notice that frozendict is not subclass of dict to follow SC feedback

Ah right, done.

bedevere-bot · 2026-02-14T12:19:13Z

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 9101b1a 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F144757%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

corona10 · 2026-02-14T12:19:43Z

Let's wait build bot to pass the refleak test :)

benediktjohannes

Nitpick: I know this does not primarily belong to the PR, but it's such a small change that a new PR wouldn't make sense for these small "typos".

Co-authored-by: Adam Johnson <me@adamj.eu>

vstinner · 2026-02-16T10:53:00Z

Let's wait build bot to pass the refleak test :)

Tests passed successfully on Refleaks buildbots:

buildbot/AMD64 CentOS9 NoGIL Refleaks PR — Build done.
buildbot/AMD64 Fedora Stable Refleaks PR — Build done.
buildbot/AMD64 FreeBSD Refleaks PR — Build done.
buildbot/AMD64 RHEL8 Refleaks PR — Build done.
buildbot/AMD64 Windows11 Refleaks PR — Build done.
buildbot/ARM64 MacOS M1 Refleaks NoGIL PR — Build done.
buildbot/PPC64LE Fedora Stable Refleaks PR — Build done.
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buildbot/s390x Fedora Stable Refleaks PR — Build done.
buildbot/s390x RHEL8 Refleaks PR — Build done.
buildbot/s390x RHEL9 Refleaks PR — Build done.

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Add also a title in Doc/library/stdtypes.rst.

vstinner · 2026-02-16T12:16:21Z

@hugovk: I modified a few more titles in the C API doc and the Python doc to use sentence case for headers.

corona10

lgtm with current implementations , I will soon create PRs for removing unneeded overhead from my side.

sergey-miryanov

Couple of nitpicks.

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Co-authored-by: Benedikt Johannes <benedikt.johannes.hofer@gmail.com>

vstinner · 2026-02-17T09:55:02Z

I merged my PR. Thank you very much for all your reviews!

pythongh-141510, PEP 814: Add built-in frozendict type
bde4379
Add TYPE_FROZENDICT to the marshal module. Add C API functions: * PyAnyDict_Check() * PyAnyDict_CheckExact() * PyFrozenDict_Check() * PyFrozenDict_CheckExact() * PyFrozenDict_New() Add PyFrozenDict_Type C type.

bedevere-appBot mentioned this pull request Feb 12, 2026
PEP 814: Add built-in frozendict type #141510
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vstinner added 2 commits February 12, 2026 19:25

Document PyFrozenDict_Type in the C API doc
1fb7c5a

Fix test_inspect and test_doctest
fca2e5b

vstinner marked this pull request as ready for review February 13, 2026 07:30

vstinner requested review from AA-Turner, ZeroIntensity, ericsnowcurrently, markshannon, methane and rhettinger as code owners February 13, 2026 07:30

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Complete the documentation
99b291c

vstinner mentioned this pull request Feb 13, 2026
[WIP] gh-141510: PEP 814: Add built-in frozendict type #141508
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Fix doc warnings
5e4a284
Fix also indentation.

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Move the What's New entry
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Document frozendict after lazy import.

Revert _PyDict_LoadBuiltinsFromGlobals() change
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Document that frozendict is not a dict subclass
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doc: use sentence case for headers
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Add also a title in Doc/library/stdtypes.rst.

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vstinner merged commit 696cdfc into python:mainFeb 17, 2026

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savannahostrowski mentioned this pull request Feb 18, 2026
dict_traverse crash during PGO training on Windows with JIT enabled #144970
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vstinner commented Feb 12, 2026•
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