bpo-31900: Fix localeconv() encoding for LC_NUMERIC (#4174)

* Add _Py_GetLocaleconvNumeric() function: decode decimal_point and
  thousands_sep fields of localeconv() from the LC_NUMERIC encoding,
  rather than decoding from the LC_CTYPE encoding.
* Modify locale.localeconv() and "n" formatter of str.format() (for
  int, float and complex to use _Py_GetLocaleconvNumeric()
  internally.

1 files changed, 10 insertions, 0 deletions

diff --git a/Doc/library/locale.rst b/Doc/library/locale.rst
index 7da94a2..2fd44fe 100644
--- a/Doc/library/locale.rst
+++ b/Doc/library/locale.rst
@@ -147,6 +147,16 @@ The :mod:`locale` module defines the following exception and functions:
    | ``CHAR_MAX`` | Nothing is specified in this locale.    |
    +--------------+-----------------------------------------+
 
+   The function sets temporarily the ``LC_CTYPE`` locale to the ``LC_NUMERIC``
+   locale to decode ``decimal_point`` and ``thousands_sep`` byte strings if
+   they are non-ASCII or longer than 1 byte, and the ``LC_NUMERIC`` locale is
+   different than the ``LC_CTYPE`` locale. This temporary change affects other
+   threads.
+
+   .. versionchanged:: 3.7
+      The function now sets temporarily the ``LC_CTYPE`` locale to the
+      ``LC_NUMERIC`` locale in some cases.
+
 
 .. function:: nl_langinfo(option)