gh-95778: Use a note for the max digits error message

Doc/library/stdtypes.rst

@@ -5493,15 +5493,17 @@ When an operation would exceed the limit, a :exc:`ValueError` is raised:
    >>> _ = int('2' * 5432)
    Traceback (most recent call last):
    ...
-   ValueError: Exceeds the limit (4300) for integer string conversion: value has 5432 digits; use sys.set_int_max_str_digits() to increase the limit.
+   ValueError: Exceeds the limit (4300) for integer string conversion: value has 5432 digits
+   Use sys.set_int_max_str_digits() to increase the limit
    >>> i = int('2' * 4300)
    >>> len(str(i))
    4300
    >>> i_squared = i*i
    >>> len(str(i_squared))
    Traceback (most recent call last):
    ...
-   ValueError: Exceeds the limit (4300) for integer string conversion: value has 8599 digits; use sys.set_int_max_str_digits() to increase the limit.
+   ValueError: Exceeds the limit (4300) for integer string conversion: value has 8599 digits
+   Use sys.set_int_max_str_digits() to increase the limit
    >>> len(hex(i_squared))
    7144
    >>> assert int(hex(i_squared), base=16) == i*i  # Hexadecimal is unlimited.

Include/internal/pycore_pyerrors.h

@@ -94,6 +94,11 @@ PyAPI_FUNC(PyObject *) _PyExc_PrepReraiseStar(
 
 PyAPI_FUNC(int) _PyErr_CheckSignalsTstate(PyThreadState *tstate);
 
+// Call add_note(note) on the current exception.
+// Return -1 on error, or 0 on success.
+// Save and restore the current exception.
+PyAPI_FUNC(int) _PyErr_AddNote(const char *note);
+
 PyAPI_FUNC(void) _Py_DumpExtensionModules(int fd, PyInterpreterState *interp);
 
 extern PyObject* _Py_Offer_Suggestions(PyObject* exception);

Objects/exceptions.c

@@ -11,6 +11,7 @@
 #include "pycore_exceptions.h"    // struct _Py_exc_state
 #include "pycore_initconfig.h"
 #include "pycore_object.h"
+#include "pycore_pyerrors.h"      // _PyErr_Restore()
 #include "structmember.h"         // PyMemberDef
 #include "osdefs.h"               // SEP
 
@@ -3833,3 +3834,38 @@ _PyErr_TrySetFromCause(const char *format, ...)
     PyErr_Restore(new_exc, new_val, new_tb);
     return new_val;
 }
+
+
+int
+_PyErr_AddNote(const char *note)
+{
+    int err = -1;
+    PyObject *str = NULL, *res = NULL;
+
+    PyThreadState *tstate = _PyThreadState_GET();
+    PyObject *exc_type, *exc_value, *exc_tb;
+    _PyErr_Fetch(tstate, &exc_type, &exc_value, &exc_tb);
+    PyErr_NormalizeException(&exc_type, &exc_value, &exc_tb);
+
+    if (exc_value == NULL) {
+        goto exit;
+    }
+
+    str = PyUnicode_FromString(note);
+    if (str == NULL) {
+        goto exit;
+    }
+
+    res = BaseException_add_note(exc_value, str);
+    if (res == NULL) {
+        goto exit;
+    }
+    err = 0;
+
+exit:
+    Py_DECREF(str);
+    Py_XDECREF(res);
+
+    _PyErr_Restore(tstate, exc_type, exc_value, exc_tb);
+    return err;
+}

Objects/longobject.c

@@ -7,6 +7,7 @@
 #include "pycore_initconfig.h"    // _PyStatus_OK()
 #include "pycore_long.h"          // _Py_SmallInts
 #include "pycore_object.h"        // _PyObject_InitVar()
+#include "pycore_pyerrors.h"      // _PyErr_AddNote()
 #include "pycore_pystate.h"       // _Py_IsMainInterpreter()
 #include "pycore_runtime.h"       // _PY_NSMALLPOSINTS
 #include "pycore_structseq.h"     // _PyStructSequence_FiniType()
@@ -36,8 +37,9 @@ medium_value(PyLongObject *x)
 #define IS_SMALL_INT(ival) (-_PY_NSMALLNEGINTS <= (ival) && (ival) < _PY_NSMALLPOSINTS)
 #define IS_SMALL_UINT(ival) ((ival) < _PY_NSMALLPOSINTS)
 
-#define _MAX_STR_DIGITS_ERROR_FMT_TO_INT "Exceeds the limit (%d) for integer string conversion: value has %zd digits; use sys.set_int_max_str_digits() to increase the limit"
-#define _MAX_STR_DIGITS_ERROR_FMT_TO_STR "Exceeds the limit (%d) for integer string conversion; use sys.set_int_max_str_digits() to increase the limit"
+#define _MAX_STR_DIGITS_ERROR_FMT_TO_INT "Exceeds the limit (%d) for integer string conversion: value has %zd digits"
+#define _MAX_STR_DIGITS_ERROR_FMT_TO_STR "Exceeds the limit (%d) for integer string conversion"
+#define _MAX_STR_DIGITS_ERROR_NOTE "Use sys.set_int_max_str_digits() to increase the limit"
 
 static inline void
 _Py_DECREF_INT(PyLongObject *op)
@@ -1732,6 +1734,14 @@ rem1(PyLongObject *a, digit n)
     );
 }
 
+
+static void
+long_error_add_max_digits_note(void)
+{
+    (void)_PyErr_AddNote(_MAX_STR_DIGITS_ERROR_NOTE);
+}
+
+
 /* Convert an integer to a base 10 string.  Returns a new non-shared
    string.  (Return value is non-shared so that callers can modify the
    returned value if necessary.) */
@@ -1772,6 +1782,7 @@ long_to_decimal_string_internal(PyObject *aa,
             (max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10)) {
             PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_STR,
                          max_str_digits);
+            long_error_add_max_digits_note();
             return -1;
         }
     }
@@ -1843,6 +1854,7 @@ long_to_decimal_string_internal(PyObject *aa,
             Py_DECREF(scratch);
             PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_STR,
                          max_str_digits);
+            long_error_add_max_digits_note();
             return -1;
         }
     }
@@ -2518,6 +2530,7 @@ digit beyond the first.
             if ((max_str_digits > 0) && (digits > max_str_digits)) {
                 PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_INT,
                              max_str_digits, digits);
+                long_error_add_max_digits_note();
                 return NULL;
             }
         }