From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Date: Mon, 2 Dec 2024 13:52:49 +0000 (+0100) Subject: [3.12] gh-99880: document rounding mode for new-style formatting (GH-121481) (#126335) X-Git-Tag: v3.12.8~11 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=22f8e430f81b8b8966bff0efe65786515a132b7e;p=thirdparty%2FPython%2Fcpython.git [3.12] gh-99880: document rounding mode for new-style formatting (GH-121481) (#126335) The CPython uses _Py_dg_dtoa(), which does rounding to nearest with half to even tie-breaking rule. If that functions is unavailable, PyOS_double_to_string() fallbacks to system snprintf(). Since CPython 3.12, build requirements include C11 compiler *and* support for IEEE 754 floating point numbers (Annex F). This means that FE_TONEAREST macro is available and, per default, printf-like functions should use same rounding mode as _Py_dg_dtoa(). (cherry picked from commit 7d7d56d8b1147a6b85e1c09d01b164df7c5c4942) Co-authored-by: Sergey B Kirpichev Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> --- diff --git a/Doc/library/string.rst b/Doc/library/string.rst index 9e8e44a8abe7..a000bb49f148 100644 --- a/Doc/library/string.rst +++ b/Doc/library/string.rst @@ -589,6 +589,11 @@ The available presentation types for :class:`float` and | | as altered by the other format modifiers. | +---------+----------------------------------------------------------+ +The result should be correctly rounded to a given precision ``p`` of digits +after the decimal point. The rounding mode for :class:`float` matches that +of the :func:`round` builtin. For :class:`~decimal.Decimal`, the rounding +mode of the current :ref:`context ` will be used. + The available presentation types for :class:`complex` are the same as those for :class:`float` (``'%'`` is not allowed). Both the real and imaginary components of a complex number are formatted as floating-point numbers, according to the