raise TypeError when `iter` method is `None`#7092

elmjag

Setting special __iter__ method to None is used to mark objects as non-iterable.

https://docs.python.org/3/reference/datamodel.html#special-method-names

Check if __iter__ is set to None and raise TypeError exception.

Summary by CodeRabbit

Bug Fixes
- Enhanced error reporting for iteration operations with clearer, more precise error messages when attempting to iterate over non-iterable objects
- Improved exception handling to distinguish between different iteration failure scenarios

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📝 Walkthrough

Walkthrough

The iter_wrapper function in slot.rs was refactored to explicitly look up the __iter__ special method on objects rather than directly invoking it, with added error handling to distinguish between missing methods and methods explicitly set to None, raising appropriate AttributeError or TypeError exceptions.

Changes

Cohort / File(s)	Summary
Iterator wrapper enhancement `crates/vm/src/types/slot.rs`	Refactored `iter_wrapper` to perform explicit `__iter__` method lookup with None-checking logic; raises `AttributeError` when method is missing and `TypeError` when explicitly set to None; added `PyMethod` import to support method resolution.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

More slot impl #6618: Modifies slot method resolution and ownership handling logic in the same file, affecting how special methods are accessed and wrapped.
iter with slot-wrapper #6488: Changes iterator protocol implementation by replacing direct __iter__ invocation with explicit slot-based method lookup and resolution, directly related to this iterator handling enhancement.

Poem

🐰 A hop through slots, a method to find,
No more direct calls of the blind,
Explicit lookup, errors ring clear,
When None means "not iterable here!"
The rabbit approves of semantics so fine! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 pull request title clearly and specifically describes the main change: raising a TypeError when the iter method is None, which matches the core objective of implementing proper handling for non-iterable objects.

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Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@crates/vm/src/types/slot.rs`:
- Around line 548-551: Replace the AttributeError raised when __iter__ is
missing with a TypeError: in the block that calls vm.get_special_method(&zelf,
identifier!(vm, __iter__)), change the ok_or_else(...) from
vm.new_attribute_error(...) to vm.new_type_error(...) and construct the message
as "'<ClassName>' object is not iterable" using the object's class name (e.g.,
format!("'{}' object is not iterable", zelf.class().name())). Keep the existing
method_is_none() TypeError behavior unchanged.

🧹 Nitpick comments (2)

crates/vm/src/types/slot.rs (2)
545-551: Decorative comment separators violate coding guidelines.

Lines 545–547 and 553–556 use blank // lines as section separators. As per coding guidelines, "Do not add decorative section separators (e.g. // -----------, // ===, /* *** */). Use /// doc-comments or short // comments only when they add value."
Proposed fix: collapse to single-line comments
-    //
-    // look-up '__iter__' method
-    //
+    // Look up __iter__ method
     let method_ident = identifier!(vm, __iter__);
     let method = vm
         .get_special_method(&zelf, method_ident)?
         .ok_or_else(|| vm.new_attribute_error(method_ident.as_str().to_owned()))?;

-    //
-    // setting '__iter__' method to 'None' value is used
-    // to mark non-iterable objects, raise TypeError
-    //
+    // __iter__ = None marks non-iterable objects
     if method_is_none(&method, vm) {
537-562: Consider consistency with __hash__ = None handling.

The __hash__ = None case (lines 758–783) is handled at slot-update time by storing hash_not_implemented as the slot function. The __iter__ = None case is handled at call time inside the wrapper. Both approaches work, but the inconsistency may confuse future maintainers. If there's no strong reason to differ, consider aligning the pattern (e.g., storing a dedicated iter_not_implemented function during slot update, similar to hash_not_implemented).

That said, CPython's slot_tp_iter also checks at call time, so the current approach is arguably more faithful to CPython.

ShaharNaveh

Thanks for the PR!
I don't think that the failed CI is related to your change, I'll investigate

ShaharNaveh

yup: rust-lang/miri#4855

elmjag

yup: rust-lang/miri#4855

Thanks for investigating!

ShaharNaveh

@elmjag please merge main, it should pass now

elmjag

537-562: Consider consistency with __hash__ = None handling.
The __hash__ = None case (lines 758–783) is handled at slot-update time by storing hash_not_implemented as the slot function. The __iter__ = None case is handled at call time inside the wrapper. Both approaches work, but the inconsistency may confuse future maintainers. If there's no strong reason to differ, consider aligning the pattern (e.g., storing a dedicated iter_not_implemented function during slot update, similar to hash_not_implemented).
That said, CPython's slot_tp_iter also checks at call time, so the current approach is arguably more faithful to CPython.

I'll look into using this approach for __iter__ = None case. Sounds like a better way to implement it, marking this PR as draft for now.

Setting special `__iter__` method to `None` is used to mark objects as non-iterable. https://docs.python.org/3/reference/datamodel.html#special-method-names Check if `__iter__` is set to `None` and raise TypeError exception.

github-actions

📦 Library Dependencies

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

[x] lib: cpython/Lib/typing.py
[ ] test: cpython/Lib/test/test_typing.py (TODO: 6)
[x] test: cpython/Lib/test/test_type_aliases.py
[x] test: cpython/Lib/test/test_type_annotations.py (TODO: 1)
[x] test: cpython/Lib/test/test_type_params.py (TODO: 10)
[x] test: cpython/Lib/test/test_genericalias.py

dependencies:

typing

dependent tests: (12 tests)

typing: test_annotationlib test_builtin test_enum test_fractions test_functools test_genericalias test_grammar test_isinstance test_type_aliases test_type_params test_types test_typing

Legend:

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

ShaharNaveh

@elmjag can you please resolve the conflicts? I think it can be merged

elmjag

@elmjag can you please resolve the conflicts? I think it can be merged

This issue is now fixed, via #7091. Closing this PR.

coderabbitai Bot reviewed Feb 12, 2026

View reviewed changes

ShaharNaveh mentioned this pull request Feb 12, 2026

fix miri ci #7093

Merged

elmjag marked this pull request as draft February 12, 2026 15:20

raise TypeError when __iter__ method is None …

bdcc047

Setting special `__iter__` method to `None` is used to mark objects as non-iterable. https://docs.python.org/3/reference/datamodel.html#special-method-names Check if `__iter__` is set to `None` and raise TypeError exception.

elmjag force-pushed the iter-meth-none branch from e131b7c to bdcc047 Compare February 12, 2026 16:34

elmjag closed this Feb 23, 2026

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raise TypeError when `iter` method is `None`#7092