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bpo-38530: Refactor and improve AttributeError suggestions (GH-25776)

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- Make case-swaps half the cost of any other edit
- Refactor Levenshtein code to not use memory allocator, and to bail early on no match.
- Add comments to Levenshtein distance code
- Add test cases for Levenshtein distance behind a debug macro
- Set threshold to `(name_size + item_size + 3) * MOVE_COST / 6`.
  - Reasoning: similar to `difflib.SequenceMatcher.ratio()` >= 2/3:
```
"Multiset Jaccard similarity" >= 2/3
matching letters / total letters >= 2/3
(name_size - distance + item_size - distance) / (name_size + item_size) >= 2/3
1 - (2*distance) / (name_size + item_size) >= 2/3
1/3 >= (2*distance) / (name_size + item_size)
(name_size + item_size) / 6 >= distance
With rounding:
(name_size + item_size + 3) // 6 >= distance
```

Co-authored-by: Pablo Galindo <pablogsal@gmail.com>
This commit is contained in:
Dennis Sweeney 2021-05-03 11:47:27 -04:00 • committed by GitHub
parent c715b52421
commit 80a2a4ed7d
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4 changed files with 303 additions and 77 deletions
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2
Include/internal/pycore_pyerrors.h
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@ -87,6 +87,8 @@ PyAPI_FUNC(int) _PyErr_CheckSignalsTstate(PyThreadState *tstate);
PyAPI_FUNC(void) _Py_DumpExtensionModules(int fd, PyInterpreterState *interp);
extern PyObject* _Py_Offer_Suggestions(PyObject* exception);
PyAPI_FUNC(Py_ssize_t) _Py_UTF8_Edit_Cost(PyObject *str_a, PyObject *str_b,
Py_ssize_t max_cost);
#ifdef __cplusplus
}