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GeezerVison is showing github.com — gh-141510, PEP 814: Add built-in frozendict type by vstinner · Pull Request #144757 · python/cpython

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@vstinner

@vstinner vstinner commented Feb 12, 2026 •
edited by hugovk
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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

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@vstinner
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-app bedevere-app Bot mentioned this pull request Feb 12, 2026
PEP 814: Add built-in frozendict type #141510
Closed
vstinner added 2 commits February 12, 2026 19:25
@vstinner
Document PyFrozenDict_Type in the C API doc
1fb7c5a
@vstinner
Fix test_inspect and test_doctest
fca2e5b
@vstinner
vstinner marked this pull request as ready for review February 13, 2026 07:30
@vstinner
vstinner requested review from AA-Turner, ZeroIntensity, ericsnowcurrently, markshannon, methane and rhettinger as code owners February 13, 2026 07:30
@bedevere-app bedevere-app Bot added the awaiting core review label Feb 13, 2026
@vstinner
Complete the documentation
99b291c
@vstinner

vstinner commented Feb 13, 2026

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cc @corona10
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@vstinner vstinner mentioned this pull request Feb 13, 2026
[WIP] gh-141510: PEP 814: Add built-in frozendict type #141508
Closed
@vstinner
Fix doc warnings
5e4a284 
Fix also indentation.
@corona10
corona10 self-requested a review February 13, 2026 10:07
hugovk
hugovk reviewed Feb 13, 2026
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Co-authored-by: Hugo van Kemenade <[email protected]>
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Comment thread Objects/dictobject.c
}

if (PyDict_CheckExact(d)) {
if (PyAnyDict_CheckExact(d)) {

@corona10 corona10 Feb 13, 2026

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

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@vstinner vstinner Feb 13, 2026

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

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corona10
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Comment thread Objects/dictobject.c
dict_length(PyObject *self)
{
return FT_ATOMIC_LOAD_SSIZE_RELAXED(((PyDictObject *)self)->ma_used);
return GET_USED(_PyAnyDict_CAST(self));

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Do we have to use atomic operation for frozendict?

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@vstinner vstinner Feb 13, 2026

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No, we can skip the atomic operation for frozendict.

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@kumaraditya303 kumaraditya303 Feb 13, 2026

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

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@vstinner vstinner Feb 17, 2026

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len(frozendict) has been optimized by #144913.

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corona10
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Comment thread Objects/dictobject.c
};

static PyMappingMethods frozendict_as_mapping = {
.mp_length = dict_length,

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I think that we can make frozendict_lenth

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I propose to make such optimization in a separated PR.

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corona10
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Comment thread Objects/dictobject.c

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

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

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

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vstinner and others added 3 commits February 13, 2026 15:46
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8d4ed14 
Co-authored-by: Hugo van Kemenade <[email protected]>
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Move the What's New entry
c770613 
Document frozendict after lazy import.
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Revert _PyDict_LoadBuiltinsFromGlobals() change
6dfec48
vstinner
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Comment thread Objects/dictobject.c
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)

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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 :-)

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Yeah I will take a look at it

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Comment thread Objects/dictobject.c
if (items == NULL) {
return -1;
}
PyObject *frozenset = PyFrozenSet_New(items);

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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.

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I changed the implementation in #144919.

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Document that frozendict is not a dict subclass
9101b1a
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We should notice that frozendict is not subclass of dict to follow SC feedback

Ah right, done.
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@corona10 corona10 added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Feb 14, 2026
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🤖 New build scheduled with the buildbot fleet by @corona10 for commit 9101b1a 🤖

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

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@bedevere-bot bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label Feb 14, 2026
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Let's wait build bot to pass the refleak test :)
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benediktjohannes reviewed Feb 14, 2026
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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".

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Update Doc/library/stdtypes.rst
e845b2b 
Co-authored-by: Adam Johnson <[email protected]>
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Let's wait build bot to pass the refleak test :)

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hugovk
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vstinner and others added 2 commits February 16, 2026 13:01
@vstinner @hugovk
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3d08f46 
Co-authored-by: Hugo van Kemenade <[email protected]>
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doc: use sentence case for headers
258b3df 
Add also a title in Doc/library/stdtypes.rst.
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@hugovk: I modified a few more titles in the C API doc and the Python doc to use sentence case for headers.
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corona10
corona10 approved these changes Feb 16, 2026
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lgtm with current implementations , I will soon create PRs for removing unneeded overhead from my side.

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Feb 16, 2026
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Couple of nitpicks.

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vstinner and others added 2 commits February 16, 2026 21:33
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Add tests on repr(frozendict)
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Co-authored-by: Hugo van Kemenade <[email protected]>
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vstinner merged commit 696cdfc into python:main Feb 17, 2026
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I merged my PR. Thank you very much for all your reviews!
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@savannahostrowski savannahostrowski mentioned this pull request Feb 18, 2026
dict_traverse crash during PGO training on Windows with JIT enabled #144970
Closed
brijkapadia pushed a commit to brijkapadia/cpython that referenced this pull request Feb 28, 2026
@vstinner @hugovk
@adamchainz @benediktjohannes @brijkapadia
pythongh-141510, PEP 814: Add built-in frozendict type (python#144757)
1044beb 
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.

Co-authored-by: Hugo van Kemenade <[email protected]>
Co-authored-by: Adam Johnson <[email protected]>
Co-authored-by: Benedikt Johannes <[email protected]>
ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
@vstinner @hugovk
@adamchainz @benediktjohannes @ljfp
pythongh-141510, PEP 814: Add built-in frozendict type (python#144757)
fa77761 
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.

Co-authored-by: Hugo van Kemenade <[email protected]>
Co-authored-by: Adam Johnson <[email protected]>
Co-authored-by: Benedikt Johannes <[email protected]>
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@corona10 corona10 corona10 approved these changes
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