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#include "Python.h"
#include "pycore_pyerrors.h"
#define MAX_DISTANCE 3
#define MAX_CANDIDATE_ITEMS 100
#define MAX_STRING_SIZE 20
/* Calculate the Levenshtein distance between string1 and string2 */
static size_t
levenshtein_distance(const char *a, const char *b) {
if (a == NULL || b == NULL) {
return 0;
}
const size_t a_size = strlen(a);
const size_t b_size = strlen(b);
if (a_size > MAX_STRING_SIZE || b_size > MAX_STRING_SIZE) {
return 0;
}
// Both strings are the same (by identity)
if (a == b) {
return 0;
}
// The first string is empty
if (a_size == 0) {
return b_size;
}
// The second string is empty
if (b_size == 0) {
return a_size;
}
size_t *buffer = PyMem_Calloc(a_size, sizeof(size_t));
if (buffer == NULL) {
return 0;
}
// Initialize the buffer row
size_t index = 0;
while (index < a_size) {
buffer[index] = index + 1;
index++;
}
size_t b_index = 0;
size_t result = 0;
while (b_index < b_size) {
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;
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;
}
}
buffer[index] = result;
}
}
PyMem_Free(buffer);
return result;
}
static inline PyObject *
calculate_suggestions(PyObject *dir,
PyObject *name) {
assert(!PyErr_Occurred());
assert(PyList_CheckExact(dir));
Py_ssize_t dir_size = PyList_GET_SIZE(dir);
if (dir_size >= MAX_CANDIDATE_ITEMS) {
return NULL;
}
Py_ssize_t suggestion_distance = PyUnicode_GetLength(name);
PyObject *suggestion = NULL;
for (int i = 0; i < dir_size; ++i) {
PyObject *item = PyList_GET_ITEM(dir, i);
const char *name_str = PyUnicode_AsUTF8(name);
if (name_str == NULL) {
PyErr_Clear();
continue;
}
Py_ssize_t current_distance = levenshtein_distance(PyUnicode_AsUTF8(name), PyUnicode_AsUTF8(item));
if (current_distance == 0 || current_distance > MAX_DISTANCE) {
continue;
}
if (!suggestion || current_distance < suggestion_distance) {
suggestion = item;
suggestion_distance = current_distance;
}
}
if (!suggestion) {
return NULL;
}
Py_INCREF(suggestion);
return suggestion;
}
static PyObject *
offer_suggestions_for_attribute_error(PyAttributeErrorObject *exc) {
PyObject *name = exc->name; // borrowed reference
PyObject *obj = exc->obj; // borrowed reference
// Abort if we don't have an attribute name or we have an invalid one
if (name == NULL || obj == NULL || !PyUnicode_CheckExact(name)) {
return NULL;
}
PyObject *dir = PyObject_Dir(obj);
if (dir == NULL) {
return NULL;
}
PyObject *suggestions = calculate_suggestions(dir, name);
Py_DECREF(dir);
return suggestions;
}
// Offer suggestions for a given exception. Returns a python string object containing the
// suggestions. This function does not raise exceptions and returns NULL if no suggestion was found.
PyObject *_Py_Offer_Suggestions(PyObject *exception) {
PyObject *result = NULL;
assert(!PyErr_Occurred()); // Check that we are not going to clean any existing exception
if (PyErr_GivenExceptionMatches(exception, PyExc_AttributeError)) {
result = offer_suggestions_for_attribute_error((PyAttributeErrorObject *) exception);
}
assert(!PyErr_Occurred());
return result;
}
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