From 8b1525b8ae1511049a1fc0de6010414cdfda4b23 Mon Sep 17 00:00:00 2001 From: Pierre-Yves Le Borgne Date: Tue, 27 Oct 2026 01:25:45 +0000 Subject: [PATCH] Fix the libmpdec note for Python 3.15 in the build instructions Python 3.15 removed the implicit fallback to the bundled copy of libmpdec (gh-115119). Without libmpdec-dev, a default 3.15 build does not use the bundled copy: configure warns, _decimal is not built, and the decimal module uses its pure-Python implementation. The bundled copy is only used with --without-system-libmpdec, as the configure documentation for 3.15 says. Co-Authored-By: Claude Sonnet 5.5 Claude-Session: https://claude.ai/code/session_01GwUvhmzgfkiZ6vo4uGyesN --- getting-started/setup-building.rst | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/getting-started/setup-building.rst b/getting-started/setup-building.rst index 9271b5e20..e0c27c2a5 100644 --- a/getting-started/setup-building.rst +++ b/getting-started/setup-building.rst @@ -841,11 +841,13 @@ some of CPython's modules (for example, ``zlib``). inetutils-inetd Note that Debian 12 and Ubuntu 24.04 do not have the ``libmpdec-dev`` - package. You can remove it from the install list above: for Python 3.15 - and older, the build will use a bundled version; for Python 3.16 and - newer, the bundled copy has been removed and the :mod:`decimal` module - will fall back to its slower pure-Python implementation. We recommend - using the system + package. You can remove it from the install list above: for Python 3.14 + and older, the build will use a bundled version; for Python 3.15, the + build will use the bundled version only if you pass + ``--without-system-libmpdec`` to ``configure``. Otherwise, and for + Python 3.16 and newer, where the bundled copy has been removed, the + :mod:`decimal` module will fall back to its slower pure-Python + implementation. We recommend using the system `libmpdec `__ library. Either build it from sources or install this package from https://deb.sury.org.