bpo-28604: Fix localeconv() for different LC_MONETARY (GH-10606) (GH-10619) (GH-10621)

locale.localeconv() now sets temporarily the LC_CTYPE locale to the
LC_MONETARY locale if the two locales are different and monetary
strings are non-ASCII. This temporary change affects other threads.

Changes:

* locale.localeconv() can now set LC_CTYPE to LC_MONETARY to decode
  monetary fields.
* Add LocaleInfo.grouping_buffer: copy localeconv() grouping string
  since it can be replaced anytime if a different thread calls
  localeconv().

(cherry picked from commit 02e6bf7f2025cddcbde6432f6b6396198ab313f4)
(cherry picked from commit 6eff6b8eecd7a8eccad16419269fa18ec820922e)

2 files changed, 17 insertions, 4 deletions

diff --git a/Python/fileutils.c b/Python/fileutils.c
index 306838ecce..d1a9ca03a1 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -1687,7 +1687,7 @@ _Py_GetLocaleconvNumeric(PyObject **decimal_point, PyObject **thousands_sep,
     if (change_locale) {
         oldloc = setlocale(LC_CTYPE, NULL);
         if (!oldloc) {
-            PyErr_SetString(PyExc_RuntimeWarning, "faild to get LC_CTYPE locale");
+            PyErr_SetString(PyExc_RuntimeWarning, "failed to get LC_CTYPE locale");
             return -1;
         }
 
@@ -1703,7 +1703,7 @@ _Py_GetLocaleconvNumeric(PyObject **decimal_point, PyObject **thousands_sep,
         }
 
         if (loc != NULL) {
-            /* Only set the locale temporarilty the LC_CTYPE locale
+            /* Only set the locale temporarily the LC_CTYPE locale
                if LC_NUMERIC locale is different than LC_CTYPE locale and
                decimal_point and/or thousands_sep are non-ASCII or longer than
                1 byte */
diff --git a/Python/formatter_unicode.c b/Python/formatter_unicode.c
index d6772c5938..c9a2c99dd2 100644
--- a/Python/formatter_unicode.c
+++ b/Python/formatter_unicode.c
@@ -397,9 +397,10 @@ typedef struct {
     PyObject *decimal_point;
     PyObject *thousands_sep;
     const char *grouping;
+    char *grouping_buffer;
 } LocaleInfo;
 
-#define STATIC_LOCALE_INFO_INIT {0, 0, 0}
+#define STATIC_LOCALE_INFO_INIT {0, 0, 0, 0}
 
 /* describes the layout for an integer, see the comment in
    calc_number_widths() for details */
@@ -708,11 +709,22 @@ get_locale_info(enum LocaleType type, LocaleInfo *locale_info)
 {
     switch (type) {
     case LT_CURRENT_LOCALE: {
+        const char *grouping;
         if (_Py_GetLocaleconvNumeric(&locale_info->decimal_point,
                                      &locale_info->thousands_sep,
-                                     &locale_info->grouping) < 0) {
+                                     &grouping) < 0) {
             return -1;
         }
+
+        /* localeconv() grouping can become a dangling pointer or point
+           to a different string if another thread calls localeconv() during
+           the string formatting. Copy the string to avoid this risk. */
+        locale_info->grouping_buffer = _PyMem_Strdup(grouping);
+        if (locale_info->grouping_buffer == NULL) {
+            PyErr_NoMemory();
+            return -1;
+        }
+        locale_info->grouping = locale_info->grouping_buffer;
         break;
     }
     case LT_DEFAULT_LOCALE:
@@ -746,6 +758,7 @@ free_locale_info(LocaleInfo *locale_info)
 {
     Py_XDECREF(locale_info->decimal_point);
     Py_XDECREF(locale_info->thousands_sep);
+    PyMem_Free(locale_info->grouping_buffer);
 }
 
 /************************************************************************/