Python makes various references to IEEE 754 floating point operations, but doesn't guarantee 1 2 that it'll be used at runtime. I'm therefore wondering where this isn't the case.

CPython source code defers to whatever the C compiler is using for a double, which in practice is an IEEE 754-2008 binary64 on all common systems I'm aware of, e.g.:

• Linux and BSD distros (e.g. FreeBSD, OpenBSD, NetBSD)
  • Intel i386/x86 and x86-64
  • ARM: AArch64
  • Power: PPC64
• MacOS all architectures supported are 754 compatible
• Windows x86 and x86-64 systems

I'm aware there are other platforms it's known to build on but don't know how these work out in practice.