gh-141510, PEP 814: Add frozendict support to pickle by vstinner · Pull Request #144967 · python/cpython

vstinner · 2026-02-18T18:19:20Z

Add frozendict.__getnewargs__() method.

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

Add frozendict.__getnewargs__() method.

serhiy-storchaka · 2026-02-18T21:30:01Z

 # make sure that floats are formatted locale independent with proto 0
 self.assertEqual(self.dumps(1.2, 0)[0:3], b'F1.')

+ def test_frozendict(self):


Would not be better to add this test in test_frozendict.py? Together with tests for copy() and deepcopy()?

Ok, I moved this test to test_pickle.

Together with tests for copy() and deepcopy()?
Commit dd64e42, which adds frozendict support to the copy module, added frozendict tests to test_copy.

vstinner · 2026-02-19T12:28:53Z

@serhiy-storchaka: I addressed your review. Please review the updated PR.

serhiy-storchaka

What about frozendict views and iterators? Are they copyable/pickleable?

Are there tests for deepcopying?

I am surprised that there is no separate test_frozendict.py.

serhiy-storchaka · 2026-02-19T12:55:59Z

Oh, I don't think deepcopy of frozendict is correct. It does not work for recursive frozendict.

vstinner · 2026-02-19T13:31:53Z

I will try to update my PR later to address other comments.

What about frozendict views and iterators? Are they copyable/pickleable?

keys, values and items views cannot be copied nor serialized by pickle.

Ah, it seems like it's possible to serialize a frozendict iterator.

Are there tests for deepcopying?

test_copy.test_deepcopy_frozendict() tests frozendict deepcopy.

I am surprised that there is no separate test_frozendict.py.

Ah. It was simple to add frozendict tests to existing test_dict. Maybe we can create test_frozendict later once we will add more tests.

vstinner · 2026-02-19T23:29:03Z

Oh, I don't think deepcopy of frozendict is correct. It does not work for recursive frozendict.

You're right, the current copy.deepcopy() implementation doesn't work for recursive frozendict.

vstinner · 2026-02-19T23:32:11Z

I completed the PR to add requested tests.

vstinner · 2026-02-19T23:53:21Z

You're right, the current copy.deepcopy() implementation doesn't work for recursive frozendict.

I created #145027 to fix copy.deepcopy() for recursive frozendict.

serhiy-storchaka · 2026-02-20T09:31:24Z

 pickle.dumps(fd, proto)

+ def test_pickle_iter(self):
+ it = iter(frozendict(x=1, y=2))


What about value iterator and item iterator?
Consume one item from the iterator, to ensure that it correctly restores its state. See pickling tests in test_ordered_dict for example.
If things are pickleable, they should also be deepcopyable. It is worth to have explicit deepcopy tests, because they can preserve additional invariants. For example, it should be possible to deepcopy a frozendict containing lambdas or modules.

vstinner · 2026-02-20T12:08:28Z

If things are pickleable, they should also be deepcopyable. It is worth to have explicit deepcopy tests, because they can preserve additional invariants. For example, it should be possible to deepcopy a frozendict containing lambdas or modules.

I propose merging this PR first (once it will be approved), and then adding such tests to #145027 PR.

serhiy-storchaka · 2026-02-20T13:02:55Z

Did you forget to push changes for comments which you marked resolved?

Remove also DictKey (use Object instead).

vstinner · 2026-02-20T13:26:55Z

Ooops, you're correct. I forgot to push my changes, but I also removed my local branch... I had to rewrite my changes. I just pushed them. I should be ok now.

serhiy-storchaka

LGTM. 👍

vstinner · 2026-02-21T10:08:16Z

Merged. Thanks for your great review @serhiy-storchaka, it was very useful!

StanFromIreland · 2026-02-21T10:34:51Z

This broke Oddballs (i.e. text_xpickle): https://buildbot.python.org/#/builders/1868/builds/5

vstinner · 2026-02-21T10:45:10Z

This broke Oddballs (i.e. text_xpickle): https://buildbot.python.org/#/builders/1868/builds/5

Oh, I'm not used to test_xpickle yet, I forgot about it. I wrote #145069 to fix test_xpickle.

…4967) Add frozendict.__getnewargs__() method.

pythongh-141510, PEP 814: Add frozendict support to pickle
3eb714a
Add frozendict.__getnewargs__() method.

vstinner requested review from markshannon and methane as code owners February 18, 2026 18:19

vstinner added the skip news label Feb 18, 2026

bedevere-appBot added the awaiting core review label Feb 18, 2026

vstinner mentioned this pull request Feb 18, 2026
gh-141510, PEP 814: Add frozendict support to pickle #144936
Closed

Add simple tests
d7972ff

bedevere-appBot mentioned this pull request Feb 18, 2026
PEP 814: Add built-in frozendict type #141510
Closed

serhiy-storchaka reviewed Feb 18, 2026
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vstinner added 2 commits February 19, 2026 13:13

Fix picklecommon for Python 3.14 and older
24d757a

Move pickle tests to test_dict
416a1b7

Fix test_dict.test_pickle()
9666d7e

serhiy-storchaka reviewed Feb 19, 2026
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Comment threadLib/test/test_dict.py
Comment threadLib/test/test_dict.py Outdated

serhiy-storchaka reviewed Feb 19, 2026
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Comment threadLib/test/pickletester.py

Test frozendict subclasses
2939cba

serhiy-storchaka reviewed Feb 19, 2026
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Comment threadLib/test/test_dict.py

vstinner added 2 commits February 19, 2026 23:57

Add more tests to test_dict
8162f6b

Add pickle tests on mutable key/value
64cba52

serhiy-storchaka reviewed Feb 20, 2026
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vstinner mentioned this pull request Feb 20, 2026
gh-141510: Fix copy.deepcopy() for recursive frozendict #145027
Merged

vstinner added 2 commits February 20, 2026 14:23

Add more pickle tests on iterators
90842c1

Remove redundant pickle tests
c5f7ef7
Remove also DictKey (use Object instead).

serhiy-storchaka approved these changes Feb 20, 2026
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bedevere-appBot added awaiting merge and removed awaiting core review labels Feb 20, 2026

vstinner merged commit 20b1535 into python:mainFeb 21, 2026
49 checks passed

vstinner deleted the frozendict_pickle2 branch February 21, 2026 10:07

bedevere-appBot removed the awaiting merge label Feb 21, 2026

brianschubert mentioned this pull request Feb 22, 2026
Add frozendict support to pickle #145091
Closed

brijkapadia pushed a commit to brijkapadia/cpython that referenced this pull request Feb 28, 2026
pythongh-141510, PEP 814: Add frozendict support to pickle (python#14…
2324277
…4967) Add frozendict.__getnewargs__() method.

ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
pythongh-141510, PEP 814: Add frozendict support to pickle (python#14…
ad3752a
…4967) Add frozendict.__getnewargs__() method.

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vstinner commented Feb 18, 2026•
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