bpo-38530: Offer suggestions on NameError (GH-25397)
When printing NameError raised by the interpreter, PyErr_Display
will offer suggestions of simmilar variable names in the function that the exception
was raised from:
>>> schwarzschild_black_hole = None
>>> schwarschild_black_hole
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'schwarschild_black_hole' is not defined. Did you mean: schwarzschild_black_hole?diff --git a/Python/ceval.c b/Python/ceval.c
index 53b596b..326930b 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -6319,6 +6319,20 @@ format_exc_check_arg(PyThreadState *tstate, PyObject *exc,
return;
_PyErr_Format(tstate, exc, format_str, obj_str);
+
+ if (exc == PyExc_NameError) {
+ // Include the name in the NameError exceptions to offer suggestions later.
+ _Py_IDENTIFIER(name);
+ PyObject *type, *value, *traceback;
+ PyErr_Fetch(&type, &value, &traceback);
+ PyErr_NormalizeException(&type, &value, &traceback);
+ if (PyErr_GivenExceptionMatches(value, PyExc_NameError)) {
+ // We do not care if this fails because we are going to restore the
+ // NameError anyway.
+ (void)_PyObject_SetAttrId(value, &PyId_name, obj);
+ }
+ PyErr_Restore(type, value, traceback);
+ }
}
static void
diff --git a/Python/suggestions.c b/Python/suggestions.c
index 2c0858d..058294f 100644
--- a/Python/suggestions.c
+++ b/Python/suggestions.c
@@ -1,17 +1,15 @@
#include "Python.h"
+#include "frameobject.h"
#include "pycore_pyerrors.h"
#define MAX_DISTANCE 3
#define MAX_CANDIDATE_ITEMS 100
-#define MAX_STRING_SIZE 20
+#define MAX_STRING_SIZE 25
/* 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);
@@ -89,14 +87,19 @@ calculate_suggestions(PyObject *dir,
Py_ssize_t suggestion_distance = PyUnicode_GetLength(name);
PyObject *suggestion = NULL;
+ const char *name_str = PyUnicode_AsUTF8(name);
+ if (name_str == NULL) {
+ PyErr_Clear();
+ return 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) {
+ const char *item_str = PyUnicode_AsUTF8(item);
+ if (item_str == NULL) {
PyErr_Clear();
- continue;
+ return NULL;
}
- Py_ssize_t current_distance = levenshtein_distance(PyUnicode_AsUTF8(name), PyUnicode_AsUTF8(item));
+ Py_ssize_t current_distance = levenshtein_distance(name_str, item_str);
if (current_distance == 0 || current_distance > MAX_DISTANCE) {
continue;
}
@@ -132,6 +135,48 @@ offer_suggestions_for_attribute_error(PyAttributeErrorObject *exc) {
return suggestions;
}
+
+static PyObject *
+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 an attribute name or we have an invalid one
+ if (name == NULL || traceback == NULL || !PyUnicode_CheckExact(name)) {
+ return NULL;
+ }
+
+ // Move to the traceback of the exception
+ while (traceback->tb_next != NULL) {
+ traceback = traceback->tb_next;
+ }
+
+ PyFrameObject *frame = traceback->tb_frame;
+ assert(frame != NULL);
+ PyCodeObject *code = frame->f_code;
+ assert(code != NULL && code->co_varnames != NULL);
+ PyObject *dir = PySequence_List(code->co_varnames);
+ if (dir == NULL) {
+ PyErr_Clear();
+ return NULL;
+ }
+
+ PyObject *suggestions = calculate_suggestions(dir, name);
+ Py_DECREF(dir);
+ if (suggestions != NULL) {
+ return suggestions;
+ }
+
+ dir = PySequence_List(frame->f_globals);
+ if (dir == NULL) {
+ PyErr_Clear();
+ return NULL;
+ }
+ 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) {
@@ -139,6 +184,8 @@ PyObject *_Py_Offer_Suggestions(PyObject *exception) {
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);
+ } else if (PyErr_GivenExceptionMatches(exception, PyExc_NameError)) {
+ result = offer_suggestions_for_name_error((PyNameErrorObject *) exception);
}
assert(!PyErr_Occurred());
return result;