René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Several built-in exceptions store their attributes in the instance dict instead of as fields","articleBody":"## Feature\n\nSeveral built-in exceptions store their attributes in the instance `__dict__` instead of as struct fields, so `Exc().__dict__` is non-empty (unlike CPython) and the attributes are not backed by descriptors. `SystemExit.code` (#8230 / #8282) and `StopIteration.value` (#8290 / #8301) have been converted already; this issue tracks the rest.\n\nMeasured against CPython 3.14.6 (`print(exc.__dict__)`):\n\n| exception | leaked into `__dict__` | CPython |\n|---|---|---|\n| `NameError('m', name='x')` | `{'name': 'x'}` | `{}` |\n| `AttributeError('m')` | `{'name': None, 'obj': None}` | `{}` |\n| `ImportError('m')` | `{'name': None, 'path': None, 'name_from': None}` | `{}` |\n| `SyntaxError('m')` | `{'print_file_and_line': None}` | `{}` |\n| `SyntaxError('m', (...))` | `+ filename, lineno, offset, text` | `{}` |\n| `UnicodeDecodeError(...)` | `{'encoding', 'object', 'start', 'end', 'reason'}` | `{}` |\n| `UnicodeEncodeError(...)` | same five fields | `{}` |\n| `UnicodeTranslateError(...)` | `{'object', 'start', 'end', 'reason'}` | `{}` |\n\nTheir subclasses inherit the same problem (`ModuleNotFoundError` from `ImportError`; `IndentationError` / `TabError` / `_IncompleteInputError` from `SyntaxError`) and should be fixed automatically once the base is converted.\n\nThese are the remaining cases of the issue addressed in #8282 and #8301.\n`SyntaxError` already carries a `// TODO: members` note for this.\n\n## Plan\n\nConvert each to a struct field (`#[repr(C)]` + base field, exposed via `#[pygetset]`), following the approach established in #8282 and #8301, in separate PRs:\n\n1. `NameError` and `AttributeError`\n   * Both are small and use a similar keyword-argument pattern.\n2. `ImportError`\n   * `ModuleNotFoundError` will inherit the converted fields.\n3. `UnicodeDecodeError`, `UnicodeEncodeError`, and `UnicodeTranslateError`\n   * These exceptions share most of their fields, similar to CPython's implementation.\n4. `SyntaxError`\n   * This will also cover `IndentationError`, `TabError`, and `_IncompleteInputError`.\n   * It is the largest conversion and will require checking the code paths that read these attributes.\n\n\n## Python Documentation or reference to CPython source code\n\nhttps://docs.python.org/3/library/exceptions.html\n\nThese attributes are defined via `PyMemberDef` (struct members, not instance-dict entries) in CPython's `Objects/exceptions.c`.\n\n---\nVerified locally against CPython 3.14.6 and RustPython. AI was used to help organize the initial draft; the technical details and final wording were reviewed by me.","author":{"url":"https://github.com/kangdora","@type":"Person","name":"kangdora"},"datePublished":"2026-07-21T13:47:31.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/8345/RustPython/issues/8345"}