Suggest similar member names on AttributeError for .NET objects#124
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jhonabreul merged 5 commits intoJul 1, 2026
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When accessing a missing attribute on a .NET object from Python, enrich the resulting AttributeError message with a "Did you mean ...?" hint listing similarly-named members of the managed type. The work is done inside tp_getattro where the object and attribute name are available directly, so it does not depend on the AttributeError .name/.obj attributes (Python 3.10+) and works across all supported Python versions (3.7-3.11). It only runs on the exceptional miss path, keeping normal attribute access untouched, and always re-raises an AttributeError so hasattr()/getattr(default) keep working. - ClassObject gets a tp_getattro that delegates to PyObject_GenericGetAttr and appends suggestions on a miss (inherited by EnumObject, LookUpObject, ExceptionClassObject, ClassDerivedObject). - DynamicClassObject appends suggestions on its RuntimeBinder miss path. - Shared helpers live in ClassBase (Levenshtein-based ranking, dunder names skipped, original CPython message preserved). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Martin-Molinero
approved these changes
Jun 30, 2026
The fork exposes .NET members under PEP8-style snake_case aliases, so the "Did you mean ...?" suggestions now use that form (e.g. 'length' instead of 'Length'). Conversion reuses the existing ToSnakeCase helpers, so const and static-readonly members are rendered UPPER_CASE to match how they are exposed to Python. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Style cleanup: prefer var over explicit types where the type is apparent from the right-hand side. Also drops two now-unnecessary null-forgiving operators that the compiler's flow analysis already proves non-null. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Move the suggestion logic for regular reflected types off the hot attribute-access path. Previously ClassObject overrode tp_getattro (__getattribute__), so every successful attribute access paid a managed round-trip (~17 ns/access measured). Instead, install a shared __getattr__ on each reflected type, which CPython only invokes on a miss via slot_tp_getattr_hook; hits go straight through the native generic getattr with no managed transition. pythonnet's metatype does not run CPython's slot-fixup when attributes are set on a type, so AttributeErrorHint wires tp_getattro to the hook manually (the hook address is read from a probe class). Only types still using the native generic getattr are redirected, so dynamic objects, modules and interfaces (which have their own tp_getattro) are untouched; DynamicClassObject keeps enriching on its own miss path. Benchmark (System.Version, best-of-N, ns/access): hit path: ~109 ns (baseline ~105; tp_getattro was ~122) miss path: ~11 us (rare; reflection + Levenshtein, as before) The hot-path overhead is effectively eliminated; the extra miss-path cost only applies when an attribute is actually absent. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Martin-Molinero
approved these changes
Jul 1, 2026
This was referenced Jul 1, 2026
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Summary
When Python code accesses a missing attribute on a .NET object, the resulting
AttributeErrornow includes aDid you mean ...?hint listing similarly-named members of the managed type, in snake_case (matching the fork's PEP8-style API surface):The suggestion is computed from the .NET type's members and only appears when an attribute is actually missing.
Design — miss-only
__getattr__hook (zero hot-path cost)The enrichment runs through a miss-only
__getattr__hook, so there is no cost on the common, successful attribute-access path:__getattr__after the normal lookup fails (via the nativeslot_tp_getattr_hook). On a hit it calls the generic getattr directly with no managed transition; only on a miss does it call our handler.AttributeErrorHintwirestp_getattroto the hook manually (the hook address is read from a probe class at startup). Only types still using the native generic getattr are redirected — dynamic objects, modules and interfaces (which have their owntp_getattro) are left untouched, andDynamicClassObjectenriches on its own miss path.ToSnakeCasehelpers so const/static-readonly members render asUPPER_CASE.AttributeError.name/.objattributes that only exist in 3.10+.Performance
Measured on
System.Versionproperty access, best-of-N:An earlier
tp_getattro(__getattribute__) implementation was also benchmarked; it added a consistent ~17–19 ns per attribute access on every access. A property-access-dominated Lean algorithm (~117M C# property gets) reproduced this at ~19 ns/access (~9% on that pathological loop). Across realistic Lean algorithms and a 50-algorithm regression subset, that overhead was within run-to-run noise (< 0.1% aggregate). The miss-only hook in this PR removes even that per-access cost, keeping the hit path at native speed.Changes
AttributeErrorHint.cs— sets up and installs the shared miss-only__getattr__hook on reflected types.ClassBase.cs— builds the enriched message / snake_case member suggestions (Levenshtein ranking, dunder skip); shared by the hook and byDynamicClassObject.TypeManager.cs/PythonEngine.cs— install the hook per reflected type; initialize/teardown.DynamicClassObject.cs— enriches its own attribute-miss path.tests/test_class.pyandsrc/embed_tests/TestPropertyAccess.cs.🤖 Generated with Claude Code