bpo-38530: Offer suggestions on AttributeError (#16856)

When printing AttributeError, PyErr_Display will offer suggestions of similar 
attribute names in the object that the exception was raised from:

>>> collections.namedtoplo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'collections' has no attribute 'namedtoplo'. Did you mean: namedtuple?

1 files changed, 11 insertions, 1 deletions

diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 99be629..321b04e 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -15,7 +15,7 @@
 #include "pycore_interp.h"        // PyInterpreterState.importlib
 #include "pycore_object.h"        // _PyDebug_PrintTotalRefs()
 #include "pycore_parser.h"        // _PyParser_ASTFromString()
-#include "pycore_pyerrors.h"      // _PyErr_Fetch
+#include "pycore_pyerrors.h"      // _PyErr_Fetch, _Py_Offer_Suggestions
 #include "pycore_pylifecycle.h"   // _Py_UnhandledKeyboardInterrupt
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
 #include "pycore_sysmodule.h"     // _PySys_Audit()
@@ -953,6 +953,16 @@ print_exception(PyObject *f, PyObject *value)
     if (err < 0) {
         PyErr_Clear();
     }
+    PyObject* suggestions = _Py_Offer_Suggestions(value);
+    if (suggestions) {
+        // Add a trailer ". Did you mean: (...)?"
+        err = PyFile_WriteString(". Did you mean: ", f);
+        if (err == 0) {
+            err = PyFile_WriteObject(suggestions, f, Py_PRINT_RAW);
+            err += PyFile_WriteString("?", f);
+        }
+        Py_DECREF(suggestions);
+    }
     err += PyFile_WriteString("\n", f);
     Py_XDECREF(tb);
     Py_DECREF(value);