Implement missing slots for NoneType by moreal · Pull Request #7437 · RustPython/RustPython · GitHub

This pull request does two things. First, as the title, it implements missing slots (e.g., __eq__) for NoneType.

And it lets slot traits (e.g., Comparable) implement only the slot (wrapper_descriptor), not the method. This task was ongoing, and this commit may complete it (#6486).

It will remove NoneType from whats_left.

NoneType tp_hash: https://github.com/python/cpython/blob/2f4e4ec2e7292901cab0c1466b78f5ddff48208d/Objects/object.c#L2276-L2279

static Py_hash_t none_hash(PyObject *v)
{
    return 0xFCA86420;
}

Summary by CodeRabbit

Improvements
- None now has a stable, consistent hash value (0xFCA86420 masked to 32 bits) for reliable use in sets and as dict keys.
- Rich comparisons between None and non-None values now return NotImplemented as expected.
Behavior Changes
- Some explicit Python-level dunder wrappers (comparison, descriptor, repr, and attribute-call bridges) were removed; behavior now relies on core slot implementations.
Tests
- Added tests validating None's hashing, comparison behaviors, and presence/type of comparison/hash descriptors.

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between 4ababea and 07b792b.

📒 Files selected for processing (1)

crates/vm/src/builtins/singletons.rs

📝 Walkthrough

Walkthrough

Adds Comparable and Hashable implementations for the PyNone singleton (including a fixed NONE_HASH); removes many Python-level dunder wrapper method signatures from slot-related traits; removes explicit repr wrappers for struct sequences; and expands tests to assert None's comparison behaviors and hash value.

Changes

Cohort / File(s)	Summary
PyNone Trait Implementations crates/vm/src/builtins/singletons.rs	Adds Comparable and Hashable to PyNone (pyclass attribute), implements Comparable (identical optimization → equality, otherwise NotImplemented) and Hashable returning constant NONE_HASH = 0xFCA86420.
Slot Trait API Cleanup crates/vm/src/types/slot.rs	Removes Python-level dunder method signatures from multiple traits (Destructor, Callable, GetDescriptor, GetAttr, SetAttr, Comparable rich comparisons); trims related public imports and reduces pymethod wrapper declarations.
StructSequence repr Removal crates/vm/src/types/structseq.rs	Removes explicit __repr__ pymethod wrappers for PyStructSequence and related data block, relying on slot-based slot_repr instead.
Tests: None behavior extra_tests/snippets/builtin_none.py	Adds assertions that None's rich comparisons with non-None return NotImplemented; verifies presence of comparison/hash wrapper_descriptors in type(None).__dict__ distinct from object.__dict__; asserts hash(None) masked to 32 bits equals 0xFCA86420.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

RichCompare contains pymethod. No AtomicCell for slots #6562: Modifies the Comparable/rich-comparison machinery and slot wrapper wiring closely related to adding Comparable for PyNone.
More slot impl #6618: Adjusts slot trait exposures and dunder wrapper handling similar to the slot API cleanup here.
__hash__ to slot_wrapper #6480: Changes hashing/Hashable slot surface and __hash__ handling; relates to introducing Hashable and the NONE_HASH constant.

Suggested reviewers

ShaharNaveh

Poem

🐰 I nibble slots and hop through traits,
None gets a hash in tidy slates.
When comparisons meet a stranger's face,
I whisper "NotImplemented" with gentle grace.
Happy hops and tiny bytes of delight. 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title directly and clearly describes the main objective: implementing missing type slots for NoneType, which is the primary focus of all changes across the modified files.

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📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/types.py
[ ] test: cpython/Lib/test/test_types.py (TODO: 6)

dependencies:

types

dependent tests: (52 tests)

types: test_annotationlib test_ast test_asyncgen test_asyncio test_builtin test_call test_code test_collections test_compile test_compiler_assemble test_coroutines test_decorators test_descr test_dis test_doctest test_dtrace test_dynamicclassattribute test_email test_enum test_exception_group test_fstring test_funcattrs test_generators test_genericalias test_hmac test_importlib test_inspect test_listcomps test_marshal test_monitoring test_opcache test_os test_positional_only_arg test_pprint test_pyclbr test_pydoc test_raise test_string test_subclassinit test_subprocess test_tempfile test_threading test_trace test_traceback test_type_aliases test_type_annotations test_type_params test_types test_typing test_unittest test_xml_etree test_xml_etree_c

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

As a memo, it seems 765133c commit added pymethods to Comparable again but I can't guess the reason. It may be okay if all tests pass.

🧹 Nitpick comments (1)

crates/vm/src/builtins/singletons.rs (1)
53-54: Consider adding IMMUTABLETYPE flag for consistency.

The Comparable and Hashable additions are correct. However, note that PyNotImplemented (line 122) includes flags(IMMUTABLETYPE) while PyNone does not. Both are singletons with similar semantics, so you may want to add this flag here for consistency.
Optional consistency fix
-#[pyclass(with(Constructor, AsNumber, Comparable, Hashable, Representable))]
+#[pyclass(with(Constructor, AsNumber, Comparable, Hashable, Representable), flags(IMMUTABLETYPE))]
 impl PyNone {}
🤖 Prompt for AI Agents
Verify each finding against the current code and only fix it if needed.

In `@crates/vm/src/builtins/singletons.rs` around lines 53 - 54, Add the
IMMUTABLETYPE flag to PyNone's pyclass attribute to match PyNotImplemented:
update the PyNone declaration (#[pyclass(with(Constructor, AsNumber, Comparable,
Hashable, Representable))] impl PyNone {}) to include flags(IMMUTABLETYPE) so
the singleton is marked immutable like PyNotImplemented.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@crates/vm/src/builtins/singletons.rs`:
- Around line 53-54: Add the IMMUTABLETYPE flag to PyNone's pyclass attribute to
match PyNotImplemented: update the PyNone declaration
(#[pyclass(with(Constructor, AsNumber, Comparable, Hashable, Representable))]
impl PyNone {}) to include flags(IMMUTABLETYPE) so the singleton is marked
immutable like PyNotImplemented.

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📥 Commits

Reviewing files that changed from the base of the PR and between 6a08fda and 4ababea.

📒 Files selected for processing (1)

crates/vm/src/builtins/singletons.rs

Looks good, and thank you for catching legacy python magic methods.
There must be a bunch more of those unnecessary magic methods. Could you investigate more about other methods too?

Co-authored-by: Jeong, YunWon <69878+youknowone@users.noreply.github.com>

Looks good, and thank you for catching legacy python magic methods. There must be a bunch more of those unnecessary magic methods. Could you investigate more about other methods too?

Okay, I will do in the next pull request.

* Define only wrapper_descriptor * Implement missing slots for NoneType

moreal added 2 commits March 15, 2026 23:49

Define only wrapper_descriptor

b31b812

Implement missing slots for NoneType

6d863fb

Unmark fixed tests

6a08fda

moreal marked this pull request as ready for review March 15, 2026 16:04

moreal marked this pull request as draft March 15, 2026 16:09

Inline PyNone hash value

4ababea

moreal self-assigned this Mar 15, 2026

moreal marked this pull request as ready for review March 15, 2026 16:12

coderabbitai Bot reviewed Mar 15, 2026

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moreal requested a review from youknowone March 15, 2026 16:21

youknowone approved these changes Mar 16, 2026

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youknowone requested changes Mar 16, 2026

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Comment thread crates/vm/src/builtins/singletons.rs Outdated

Improve searchability for NoneType hash value

07b792b

Co-authored-by: Jeong, YunWon <69878+youknowone@users.noreply.github.com>

moreal requested a review from youknowone March 16, 2026 02:54

youknowone approved these changes Mar 16, 2026

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youknowone merged commit 97790a8 into RustPython:main Mar 16, 2026
16 checks passed

youknowone pushed a commit to youknowone/RustPython that referenced this pull request Mar 19, 2026

Implement missing slots for NoneType (RustPython#7437 )

52c0588

* Define only wrapper_descriptor * Implement missing slots for NoneType

youknowone pushed a commit to youknowone/RustPython that referenced this pull request Mar 22, 2026

Implement missing slots for NoneType (RustPython#7437 )

9d4ceee

* Define only wrapper_descriptor * Implement missing slots for NoneType

Implement missing slots for NoneType by moreal · Pull Request #7437 · RustPython/RustPython · GitHub

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Implement missing slots for NoneType#7437
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Implement missing slots for NoneType by moreal · Pull Request #7437 · RustPython/RustPython · GitHub

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📦 Library Dependencies

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