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

- 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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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 303 additions and 77 deletions
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2
Include/internal/pycore_pyerrors.h
View File

@ -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
}

102
Lib/test/test_exceptions.py
View File

@ -1486,13 +1486,13 @@ class NameErrorTests(unittest.TestCase):
def test_name_error_suggestions_from_builtins(self):
def func():
print(AttributeErrop)
print(ZeroDivisionErrrrr)
try:
func()
except NameError as exc:
with support.captured_stderr() as err:
sys.__excepthook__(*sys.exc_info())
self.assertIn("'AttributeError'?", err.getvalue())
self.assertIn("'ZeroDivisionError'?", err.getvalue())
def test_name_error_suggestions_do_not_trigger_for_long_names(self):
def f():
@ -1565,21 +1565,87 @@ class NameErrorTests(unittest.TestCase):
def test_name_error_suggestions_do_not_trigger_for_too_many_locals(self):
def f():
# Mutating locals() is unreliable, so we need to do it by hand
a1 = a2 = a3 = a4 = a5 = a6 = a7 = a8 = a9 = a10 = a11 = a12 = a13 = \
a14 = a15 = a16 = a17 = a18 = a19 = a20 = a21 = a22 = a23 = a24 = a25 = \
a26 = a27 = a28 = a29 = a30 = a31 = a32 = a33 = a34 = a35 = a36 = a37 = \
a38 = a39 = a40 = a41 = a42 = a43 = a44 = a45 = a46 = a47 = a48 = a49 = \
a50 = a51 = a52 = a53 = a54 = a55 = a56 = a57 = a58 = a59 = a60 = a61 = \
a62 = a63 = a64 = a65 = a66 = a67 = a68 = a69 = a70 = a71 = a72 = a73 = \
a74 = a75 = a76 = a77 = a78 = a79 = a80 = a81 = a82 = a83 = a84 = a85 = \
a86 = a87 = a88 = a89 = a90 = a91 = a92 = a93 = a94 = a95 = a96 = a97 = \
a98 = a99 = a100 = a101 = a102 = a103 = a104 = a105 = a106 = a107 = \
a108 = a109 = a110 = a111 = a112 = a113 = a114 = a115 = a116 = a117 = \
a118 = a119 = a120 = a121 = a122 = a123 = a124 = a125 = a126 = \
a127 = a128 = a129 = a130 = a131 = a132 = a133 = a134 = a135 = a136 = \
a137 = a138 = a139 = a140 = a141 = a142 = a143 = a144 = a145 = \
a146 = a147 = a148 = a149 = a150 = a151 = a152 = a153 = a154 = a155 = \
a156 = a157 = a158 = a159 = a160 = a161 = None
a1 = a2 = a3 = a4 = a5 = a6 = a7 = a8 = a9 = a10 = \
a11 = a12 = a13 = a14 = a15 = a16 = a17 = a18 = a19 = a20 = \
a21 = a22 = a23 = a24 = a25 = a26 = a27 = a28 = a29 = a30 = \
a31 = a32 = a33 = a34 = a35 = a36 = a37 = a38 = a39 = a40 = \
a41 = a42 = a43 = a44 = a45 = a46 = a47 = a48 = a49 = a50 = \
a51 = a52 = a53 = a54 = a55 = a56 = a57 = a58 = a59 = a60 = \
a61 = a62 = a63 = a64 = a65 = a66 = a67 = a68 = a69 = a70 = \
a71 = a72 = a73 = a74 = a75 = a76 = a77 = a78 = a79 = a80 = \
a81 = a82 = a83 = a84 = a85 = a86 = a87 = a88 = a89 = a90 = \
a91 = a92 = a93 = a94 = a95 = a96 = a97 = a98 = a99 = a100 = \
a101 = a102 = a103 = a104 = a105 = a106 = a107 = a108 = a109 = a110 = \
a111 = a112 = a113 = a114 = a115 = a116 = a117 = a118 = a119 = a120 = \
a121 = a122 = a123 = a124 = a125 = a126 = a127 = a128 = a129 = a130 = \
a131 = a132 = a133 = a134 = a135 = a136 = a137 = a138 = a139 = a140 = \
a141 = a142 = a143 = a144 = a145 = a146 = a147 = a148 = a149 = a150 = \
a151 = a152 = a153 = a154 = a155 = a156 = a157 = a158 = a159 = a160 = \
a161 = a162 = a163 = a164 = a165 = a166 = a167 = a168 = a169 = a170 = \
a171 = a172 = a173 = a174 = a175 = a176 = a177 = a178 = a179 = a180 = \
a181 = a182 = a183 = a184 = a185 = a186 = a187 = a188 = a189 = a190 = \
a191 = a192 = a193 = a194 = a195 = a196 = a197 = a198 = a199 = a200 = \
a201 = a202 = a203 = a204 = a205 = a206 = a207 = a208 = a209 = a210 = \
a211 = a212 = a213 = a214 = a215 = a216 = a217 = a218 = a219 = a220 = \
a221 = a222 = a223 = a224 = a225 = a226 = a227 = a228 = a229 = a230 = \
a231 = a232 = a233 = a234 = a235 = a236 = a237 = a238 = a239 = a240 = \
a241 = a242 = a243 = a244 = a245 = a246 = a247 = a248 = a249 = a250 = \
a251 = a252 = a253 = a254 = a255 = a256 = a257 = a258 = a259 = a260 = \
a261 = a262 = a263 = a264 = a265 = a266 = a267 = a268 = a269 = a270 = \
a271 = a272 = a273 = a274 = a275 = a276 = a277 = a278 = a279 = a280 = \
a281 = a282 = a283 = a284 = a285 = a286 = a287 = a288 = a289 = a290 = \
a291 = a292 = a293 = a294 = a295 = a296 = a297 = a298 = a299 = a300 = \
a301 = a302 = a303 = a304 = a305 = a306 = a307 = a308 = a309 = a310 = \
a311 = a312 = a313 = a314 = a315 = a316 = a317 = a318 = a319 = a320 = \
a321 = a322 = a323 = a324 = a325 = a326 = a327 = a328 = a329 = a330 = \
a331 = a332 = a333 = a334 = a335 = a336 = a337 = a338 = a339 = a340 = \
a341 = a342 = a343 = a344 = a345 = a346 = a347 = a348 = a349 = a350 = \
a351 = a352 = a353 = a354 = a355 = a356 = a357 = a358 = a359 = a360 = \
a361 = a362 = a363 = a364 = a365 = a366 = a367 = a368 = a369 = a370 = \
a371 = a372 = a373 = a374 = a375 = a376 = a377 = a378 = a379 = a380 = \
a381 = a382 = a383 = a384 = a385 = a386 = a387 = a388 = a389 = a390 = \
a391 = a392 = a393 = a394 = a395 = a396 = a397 = a398 = a399 = a400 = \
a401 = a402 = a403 = a404 = a405 = a406 = a407 = a408 = a409 = a410 = \
a411 = a412 = a413 = a414 = a415 = a416 = a417 = a418 = a419 = a420 = \
a421 = a422 = a423 = a424 = a425 = a426 = a427 = a428 = a429 = a430 = \
a431 = a432 = a433 = a434 = a435 = a436 = a437 = a438 = a439 = a440 = \
a441 = a442 = a443 = a444 = a445 = a446 = a447 = a448 = a449 = a450 = \
a451 = a452 = a453 = a454 = a455 = a456 = a457 = a458 = a459 = a460 = \
a461 = a462 = a463 = a464 = a465 = a466 = a467 = a468 = a469 = a470 = \
a471 = a472 = a473 = a474 = a475 = a476 = a477 = a478 = a479 = a480 = \
a481 = a482 = a483 = a484 = a485 = a486 = a487 = a488 = a489 = a490 = \
a491 = a492 = a493 = a494 = a495 = a496 = a497 = a498 = a499 = a500 = \
a501 = a502 = a503 = a504 = a505 = a506 = a507 = a508 = a509 = a510 = \
a511 = a512 = a513 = a514 = a515 = a516 = a517 = a518 = a519 = a520 = \
a521 = a522 = a523 = a524 = a525 = a526 = a527 = a528 = a529 = a530 = \
a531 = a532 = a533 = a534 = a535 = a536 = a537 = a538 = a539 = a540 = \
a541 = a542 = a543 = a544 = a545 = a546 = a547 = a548 = a549 = a550 = \
a551 = a552 = a553 = a554 = a555 = a556 = a557 = a558 = a559 = a560 = \
a561 = a562 = a563 = a564 = a565 = a566 = a567 = a568 = a569 = a570 = \
a571 = a572 = a573 = a574 = a575 = a576 = a577 = a578 = a579 = a580 = \
a581 = a582 = a583 = a584 = a585 = a586 = a587 = a588 = a589 = a590 = \
a591 = a592 = a593 = a594 = a595 = a596 = a597 = a598 = a599 = a600 = \
a601 = a602 = a603 = a604 = a605 = a606 = a607 = a608 = a609 = a610 = \
a611 = a612 = a613 = a614 = a615 = a616 = a617 = a618 = a619 = a620 = \
a621 = a622 = a623 = a624 = a625 = a626 = a627 = a628 = a629 = a630 = \
a631 = a632 = a633 = a634 = a635 = a636 = a637 = a638 = a639 = a640 = \
a641 = a642 = a643 = a644 = a645 = a646 = a647 = a648 = a649 = a650 = \
a651 = a652 = a653 = a654 = a655 = a656 = a657 = a658 = a659 = a660 = \
a661 = a662 = a663 = a664 = a665 = a666 = a667 = a668 = a669 = a670 = \
a671 = a672 = a673 = a674 = a675 = a676 = a677 = a678 = a679 = a680 = \
a681 = a682 = a683 = a684 = a685 = a686 = a687 = a688 = a689 = a690 = \
a691 = a692 = a693 = a694 = a695 = a696 = a697 = a698 = a699 = a700 = \
a701 = a702 = a703 = a704 = a705 = a706 = a707 = a708 = a709 = a710 = \
a711 = a712 = a713 = a714 = a715 = a716 = a717 = a718 = a719 = a720 = \
a721 = a722 = a723 = a724 = a725 = a726 = a727 = a728 = a729 = a730 = \
a731 = a732 = a733 = a734 = a735 = a736 = a737 = a738 = a739 = a740 = \
a741 = a742 = a743 = a744 = a745 = a746 = a747 = a748 = a749 = a750 = \
a751 = a752 = a753 = a754 = a755 = a756 = a757 = a758 = a759 = a760 = \
a761 = a762 = a763 = a764 = a765 = a766 = a767 = a768 = a769 = a770 = \
a771 = a772 = a773 = a774 = a775 = a776 = a777 = a778 = a779 = a780 = \
a781 = a782 = a783 = a784 = a785 = a786 = a787 = a788 = a789 = a790 = \
a791 = a792 = a793 = a794 = a795 = a796 = a797 = a798 = a799 = a800 \
= None
print(a0)
try:
@ -1778,7 +1844,7 @@ class AttributeErrorTests(unittest.TestCase):
blech = None
# A class with a very big __dict__ will not be consider
# for suggestions.
for index in range(160):
for index in range(2000):
setattr(A, f"index_{index}", None)
try:

87
Modules/_testinternalcapi.c
View File

@ -18,6 +18,7 @@
#include "pycore_hashtable.h" // _Py_hashtable_new()
#include "pycore_initconfig.h" // _Py_GetConfigsAsDict()
#include "pycore_interp.h" // _PyInterpreterState_GetConfigCopy()
#include "pycore_pyerrors.h" // _Py_UTF8_Edit_Cost()
static PyObject *
@ -279,6 +280,91 @@ test_atomic_funcs(PyObject *self, PyObject *Py_UNUSED(args))
}
static int
check_edit_cost(const char *a, const char *b, Py_ssize_t expected)
{
int ret = -1;
PyObject *a_obj = NULL;
PyObject *b_obj = NULL;
a_obj = PyUnicode_FromString(a);
if (a_obj == NULL) {
goto exit;
}
b_obj = PyUnicode_FromString(b);
if (a_obj == NULL) {
goto exit;
}
Py_ssize_t result = _Py_UTF8_Edit_Cost(a_obj, b_obj, -1);
if (result != expected) {
PyErr_Format(PyExc_AssertionError,
"Edit cost from '%s' to '%s' returns %zd, expected %zd",
a, b, result, expected);
goto exit;
}
// Check that smaller max_edits thresholds are exceeded.
Py_ssize_t max_edits = result;
while (max_edits > 0) {
max_edits /= 2;
Py_ssize_t result2 = _Py_UTF8_Edit_Cost(a_obj, b_obj, max_edits);
if (result2 <= max_edits) {
PyErr_Format(PyExc_AssertionError,
"Edit cost from '%s' to '%s' (threshold %zd) "
"returns %zd, expected greater than %zd",
a, b, max_edits, result2, max_edits);
goto exit;
}
}
// Check that bigger max_edits thresholds don't change anything
Py_ssize_t result3 = _Py_UTF8_Edit_Cost(a_obj, b_obj, result * 2 + 1);
if (result3 != result) {
PyErr_Format(PyExc_AssertionError,
"Edit cost from '%s' to '%s' (threshold %zd) "
"returns %zd, expected %zd",
a, b, result * 2, result3, result);
goto exit;
}
ret = 0;
exit:
Py_XDECREF(a_obj);
Py_XDECREF(b_obj);
return ret;
}
static PyObject *
test_edit_cost(PyObject *self, PyObject *Py_UNUSED(args))
{
#define CHECK(a, b, n) do { \
if (check_edit_cost(a, b, n) < 0) { \
return NULL; \
} \
} while (0) \
CHECK("", "", 0);
CHECK("", "a", 2);
CHECK("a", "A", 1);
CHECK("Apple", "Aple", 2);
CHECK("Banana", "B@n@n@", 6);
CHECK("Cherry", "Cherry!", 2);
CHECK("---0---", "------", 2);
CHECK("abc", "y", 6);
CHECK("aa", "bb", 4);
CHECK("aaaaa", "AAAAA", 5);
CHECK("wxyz", "wXyZ", 2);
CHECK("wxyz", "wXyZ123", 8);
CHECK("Python", "Java", 12);
CHECK("Java", "C#", 8);
CHECK("AbstractFoobarManager", "abstract_foobar_manager", 3+2*2);
CHECK("CPython", "PyPy", 10);
CHECK("CPython", "pypy", 11);
CHECK("AttributeError", "AttributeErrop", 2);
CHECK("AttributeError", "AttributeErrorTests", 10);
#undef CHECK
Py_RETURN_NONE;
}
static PyMethodDef TestMethods[] = {
{"get_configs", get_configs, METH_NOARGS},
{"get_recursion_depth", get_recursion_depth, METH_NOARGS},
@ -289,6 +375,7 @@ static PyMethodDef TestMethods[] = {
{"get_config", test_get_config, METH_NOARGS},
{"set_config", test_set_config, METH_O},
{"test_atomic_funcs", test_atomic_funcs, METH_NOARGS},
{"test_edit_cost", test_edit_cost, METH_NOARGS},
{NULL, NULL} /* sentinel */
};

189
Python/suggestions.c
View File

@ -3,78 +3,129 @@
#include "pycore_pyerrors.h"
#define MAX_DISTANCE 3
#define MAX_CANDIDATE_ITEMS 160
#define MAX_STRING_SIZE 25
#define MAX_CANDIDATE_ITEMS 750
#define MAX_STRING_SIZE 40
#define MOVE_COST 2
#define CASE_COST 1
#define LEAST_FIVE_BITS(n) ((n) & 31)
static inline int
substitution_cost(char a, char b)
{
if (LEAST_FIVE_BITS(a) != LEAST_FIVE_BITS(b)) {
// Not the same, not a case flip.
return MOVE_COST;
}
if (a == b) {
return 0;
}
if ('A' <= a && a <= 'Z') {
a += ('a' - 'A');
}
if ('A' <= b && b <= 'Z') {
b += ('a' - 'A');
}
if (a == b) {
return CASE_COST;
}
return MOVE_COST;
}
/* Calculate the Levenshtein distance between string1 and string2 */
static Py_ssize_t
levenshtein_distance(const char *a, size_t a_size,
const char *b, size_t b_size) {
if (a_size > MAX_STRING_SIZE || b_size > MAX_STRING_SIZE) {
return 0;
}
const char *b, size_t b_size,
size_t max_cost)
{
static size_t buffer[MAX_STRING_SIZE];
// Both strings are the same (by identity)
if (a == b) {
return 0;
}
// The first string is empty
if (a_size == 0) {
return b_size;
// Trim away common affixes.
while (a_size && b_size && a[0] == b[0]) {
a++; a_size--;
b++; b_size--;
}
while (a_size && b_size && a[a_size-1] == b[b_size-1]) {
a_size--;
b_size--;
}
if (a_size == 0 || b_size == 0) {
return (a_size + b_size) * MOVE_COST;
}
if (a_size > MAX_STRING_SIZE || b_size > MAX_STRING_SIZE) {
return max_cost + 1;
}
// The second string is empty
if (b_size == 0) {
return a_size;
// Prefer shorter buffer
if (b_size < a_size) {
const char *t = a; a = b; b = t;
size_t t_size = a_size; a_size = b_size; b_size = t_size;
}
size_t *buffer = PyMem_Calloc(a_size, sizeof(size_t));
if (buffer == NULL) {
return -1;
// quick fail when a match is impossible.
if ((b_size - a_size) * MOVE_COST > max_cost) {
return max_cost + 1;
}
// Instead of producing the whole traditional len(a)-by-len(b)
// matrix, we can update just one row in place.
// Initialize the buffer row
size_t index = 0;
while (index < a_size) {
buffer[index] = index + 1;
index++;
for (size_t i = 0; i < a_size; i++) {
// cost from b[:0] to a[:i+1]
buffer[i] = (i + 1) * MOVE_COST;
}
size_t b_index = 0;
size_t result = 0;
while (b_index < b_size) {
for (size_t b_index = 0; b_index < b_size; b_index++) {
char code = b[b_index];
size_t distance = result = b_index++;
index = SIZE_MAX;
while (++index < a_size) {
size_t b_distance = code == a[index] ? distance : distance + 1;
// cost(b[:b_index], a[:0]) == b_index * MOVE_COST
size_t distance = result = b_index * MOVE_COST;
size_t minimum = SIZE_MAX;
for (size_t index = 0; index < a_size; index++) {
// cost(b[:b_index+1], a[:index+1]) = min(
// // 1) substitute
// cost(b[:b_index], a[:index])
// + substitution_cost(b[b_index], a[index]),
// // 2) delete from b
// cost(b[:b_index], a[:index+1]) + MOVE_COST,
// // 3) delete from a
// cost(b[:b_index+1], a[index]) + MOVE_COST
// )
// 1) Previous distance in this row is cost(b[:b_index], a[:index])
size_t substitute = distance + substitution_cost(code, a[index]);
// 2) cost(b[:b_index], a[:index+1]) from previous row
distance = buffer[index];
if (distance > result) {
if (b_distance > result) {
result = result + 1;
} else {
result = b_distance;
}
} else {
if (b_distance > distance) {
result = distance + 1;
} else {
result = b_distance;
}
}
// 3) existing result is cost(b[:b_index+1], a[index])
size_t insert_delete = Py_MIN(result, distance) + MOVE_COST;
result = Py_MIN(insert_delete, substitute);
// cost(b[:b_index+1], a[:index+1])
buffer[index] = result;
if (result < minimum) {
minimum = result;
}
}
if (minimum > max_cost) {
// Everything in this row is too big, so bail early.
return max_cost + 1;
}
}
PyMem_Free(buffer);
return result;
}
static inline PyObject *
calculate_suggestions(PyObject *dir,
PyObject *name) {
PyObject *name)
{
assert(!PyErr_Occurred());
assert(PyList_CheckExact(dir));
@ -83,13 +134,14 @@ calculate_suggestions(PyObject *dir,
return NULL;
}
Py_ssize_t suggestion_distance = PyUnicode_GetLength(name);
Py_ssize_t suggestion_distance = PY_SSIZE_T_MAX;
PyObject *suggestion = NULL;
Py_ssize_t name_size;
const char *name_str = PyUnicode_AsUTF8AndSize(name, &name_size);
if (name_str == NULL) {
return NULL;
}
for (int i = 0; i < dir_size; ++i) {
PyObject *item = PyList_GET_ITEM(dir, i);
Py_ssize_t item_size;
@ -97,15 +149,14 @@ calculate_suggestions(PyObject *dir,
if (item_str == NULL) {
return NULL;
}
Py_ssize_t current_distance = levenshtein_distance(
name_str, name_size, item_str, item_size);
if (current_distance == -1) {
return NULL;
}
if (current_distance == 0 ||
current_distance > MAX_DISTANCE ||
current_distance * 2 > name_size)
{
// No more than 1/3 of the involved characters should need changed.
Py_ssize_t max_distance = (name_size + item_size + 3) * MOVE_COST / 6;
// Don't take matches we've already beaten.
max_distance = Py_MIN(max_distance, suggestion_distance - 1);
Py_ssize_t current_distance =
levenshtein_distance(name_str, name_size,
item_str, item_size, max_distance);
if (current_distance > max_distance) {
continue;
}
if (!suggestion || current_distance < suggestion_distance) {
@ -113,15 +164,13 @@ calculate_suggestions(PyObject *dir,
suggestion_distance = current_distance;
}
}
if (!suggestion) {
return NULL;
}
Py_INCREF(suggestion);
Py_XINCREF(suggestion);
return suggestion;
}
static PyObject *
offer_suggestions_for_attribute_error(PyAttributeErrorObject *exc) {
offer_suggestions_for_attribute_error(PyAttributeErrorObject *exc)
{
PyObject *name = exc->name; // borrowed reference
PyObject *obj = exc->obj; // borrowed reference
@ -142,7 +191,8 @@ offer_suggestions_for_attribute_error(PyAttributeErrorObject *exc) {
static PyObject *
offer_suggestions_for_name_error(PyNameErrorObject *exc) {
offer_suggestions_for_name_error(PyNameErrorObject *exc)
{
PyObject *name = exc->name; // borrowed reference
PyTracebackObject *traceback = (PyTracebackObject *) exc->traceback; // borrowed reference
// Abort if we don't have a variable name or we have an invalid one
@ -194,7 +244,9 @@ offer_suggestions_for_name_error(PyNameErrorObject *exc) {
// Offer suggestions for a given exception. Returns a python string object containing the
// suggestions. This function returns NULL if no suggestion was found or if an exception happened,
// users must call PyErr_Occurred() to disambiguate.
PyObject *_Py_Offer_Suggestions(PyObject *exception) {
PyObject *
_Py_Offer_Suggestions(PyObject *exception)
{
PyObject *result = NULL;
assert(!PyErr_Occurred());
if (Py_IS_TYPE(exception, (PyTypeObject*)PyExc_AttributeError)) {
@ -205,3 +257,22 @@ PyObject *_Py_Offer_Suggestions(PyObject *exception) {
return result;
}
Py_ssize_t
_Py_UTF8_Edit_Cost(PyObject *a, PyObject *b, Py_ssize_t max_cost)
{
assert(PyUnicode_Check(a) && PyUnicode_Check(b));
Py_ssize_t size_a, size_b;
const char *utf8_a = PyUnicode_AsUTF8AndSize(a, &size_a);
if (utf8_a == NULL) {
return -1;
}
const char *utf8_b = PyUnicode_AsUTF8AndSize(b, &size_b);
if (utf8_b == NULL) {
return -1;
}
if (max_cost == -1) {
max_cost = MOVE_COST * Py_MAX(size_a, size_b);
}
return levenshtein_distance(utf8_a, size_a, utf8_b, size_b, max_cost);
}