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I feel that the addition, as proposed, does not make the PEP clearer for most people. And IEEE floating point is what’s provided by all supported platforms.

I think at least https://en.wikipedia.org/wiki/Extreme_programming or other link for XP could be added.

I know you can by now expect IEEE floating point, and in all C compilers. Maybe write "C11 with IEEE floating-point, and otherwise no optional features"?

I forget does Python use 64-bit floats on all platforms, or 80-bit (registers) on x86 (with 64-bit for storage format)?

Would it be better to list the optional features? Or remove the note entirely, and leave the necessary standards extensions unspecified?

In addition to the Annex F floats, CPython 3.13 now also needs C11 atomics (or MSVC).

@encukou, Is Annex F is required? Up to date build requirements says:
"A C11 compiler. Optional C11 features are not required.
[...]
Support for IEEE 754 floating-point numbers and floating-point Not-a-Number (NaN)."

Strictly speaking, this is a requirement for the platform, i.e. to binary format for doubles, not to arithmetic, for example. And I'm not sure that configure script will fail, if neither DOUBLE_IS_* macro defined. CC @vstinner.

C17 says: "An implementation that defines __STDC_IEC_559__ shall conform to the specifications in this annex." And:

sk@note:~/src/cpython $ git grep __STDC_IEC_559__ || echo "I've had worse."
I've had worse.

Edit, for context:

• https://mail.python.org/archives/list/[email protected]/thread/J5FSP6J4EITPY5C2UJI7HSL2GQCTCUWN/
• Require IEEE 754 floating point to build Python 3.11 cpython#91073

Yeah, “floating-point numbers” is a bit vague -- AFAIK, we require some things (a NaN, infinities); for some we probably have tests but the language won't break if you ignore failures (like arithmetic behaviour); but don't need everything from the annex.
#ifdef __STDC_IEC_559__ would check for strict compliance; rather than checking that we'll fail on individual pieces that are missing.

So, yeah, best left as a platform requtrement rather than a C standard requirement.

This is sort of a nitpick/question.

But practically: we only test a handful of platforms (see PEP 11). If you have a platform/compiler where Python doesn't compile, we can take (small) patches but can't guarantee they'll continue working.

I'll close this issue; if you want more discussion it's better to have it on Discourse.