I would like to remove #include <stdlib.h> from Python.h, and make Python.h smaller.

New changeset 47717d1186563695e798b40350d15b00d04a5237 by Victor Stinner in branch 'main':
bpo-45434: Cleanup Python.h header file (GH-28883)
https://github.com/python/cpython/commit/47717d1186563695e798b40350d15b00d04a5237

New changeset 03ea862b8a8234176761240ba122254e9eb11663 by Victor Stinner in branch 'main':
bpo-45434: Python.h no longer includes <stdlib.h> (GH-28888)
https://github.com/python/cpython/commit/03ea862b8a8234176761240ba122254e9eb11663

New changeset 489176e4285314f9ea87b8bd91fe1d55d9af2c42 by Victor Stinner in branch 'main':
bpo-45434: Convert Py_GETENV() macro to a function (GH-28912)
https://github.com/python/cpython/commit/489176e4285314f9ea87b8bd91fe1d55d9af2c42

New changeset c63623a0a6892ce8683dbf8c769793ea897e6ba8 by Victor Stinner in branch 'main':
bpo-45434: bytearrayobject.h no longer includes <stdarg.h> (GH-28913)
https://github.com/python/cpython/commit/c63623a0a6892ce8683dbf8c769793ea897e6ba8

New changeset 97308dfcdc0696e0b116c37386e2ff4d72e6c3f4 by Victor Stinner in branch 'main':
bpo-45434: Move _Py_BEGIN_SUPPRESS_IPH to pycore_fileutils.h (GH-28922)
https://github.com/python/cpython/commit/97308dfcdc0696e0b116c37386e2ff4d72e6c3f4

New changeset bbe7497c5a44c2b4ec726605cf5a9086ba02daf1 by Victor Stinner in branch 'main':
bpo-45434: Remove pystrhex.h header file (GH-28923)
https://github.com/python/cpython/commit/bbe7497c5a44c2b4ec726605cf5a9086ba02daf1

Oh, Include/errcode.h *is* used by PyRun_InteractiveOneFlags() and its variants. It's mentioned in its documentation:

   Returns ``0`` when the input was
   executed successfully, ``-1`` if there was an exception, or an error code
   from the :file:`errcode.h` include file distributed as part of Python if
   there was a parse error.  (Note that :file:`errcode.h` is not included by
   :file:`Python.h`, so must be included specifically if needed.)

New changeset 713bb19356bce9b8f2b95461834fe1dae505f889 by Victor Stinner in branch 'main':
bpo-45434: Mark the PyTokenizer C API as private (GH-28924)
https://github.com/python/cpython/commit/713bb19356bce9b8f2b95461834fe1dae505f889

PyRun_InteractiveOneObjectEx() returns a single error code of errcode.h: E_EOF (11):

    if (mod == NULL) {
        _PyArena_Free(arena);
        if (errcode == E_EOF) {
            PyErr_Clear();
            return E_EOF;
        }
        return -1;
    }

New changeset aac29af6785712019d34f1a7f15b3c408a4f68ae by Victor Stinner in branch 'main':
bpo-45434: pyport.h no longer includes <stdlib.h> (GH-28914)
https://github.com/python/cpython/commit/aac29af6785712019d34f1a7f15b3c408a4f68ae

I tried to remove the <string.h> include from Python.h:

-#include <string.h>               // memcpy()

... but it required me to modify 100+ files. I don't know the exact number, I gave up after 100 files. I was near half of C extensions built by setup.py, so the number total may be around 150 files which should include explicitly <string.h>.

"#include <errno.h>" can now be removed from Python.h, but I'm not sure if it's a good idea. I started by removing <stdlib.h> and my plan is to see if it breaks third party C extensions. Right now, Cython is broken which prevents me to use my https://github.com/vstinner/pythonci tool :-(

New changeset 284994762d820d8e09cc019f8f7c4bc501e37dd4 by Victor Stinner in branch 'main':
bpo-45434: Limited Python.h no longer includes stdio.h (GH-28960)
https://github.com/python/cpython/commit/284994762d820d8e09cc019f8f7c4bc501e37dd4

New changeset 7076bef8ba8836a19d5033f4ceb8eb9837de2301 by Victor Stinner in branch 'main':
bpo-45434: Remove useless space in includes (GH-28963)
https://github.com/python/cpython/commit/7076bef8ba8836a19d5033f4ceb8eb9837de2301

New changeset 105582e74c1817bc6a9d99bcb6540b34a3367292 by Victor Stinner in branch 'main':
bpo-45434: Remove Include/eval.h header file (GH-28973)
https://github.com/python/cpython/commit/105582e74c1817bc6a9d99bcb6540b34a3367292

New changeset fd03917786a9036ee87b7df604dfb260cc2420c9 by Dong-hee Na in branch 'main':
bpo-45434: Include stdlib.h for specialize stat (GH-29015)
https://github.com/python/cpython/commit/fd03917786a9036ee87b7df604dfb260cc2420c9

Victor, what's the benefit of doing this work? Are there real problems this fixes? I'm worried about the churn in third-party extensions, examples, tutorials, etc, especially for audiences that upon seeing a compiler error won't immediately realise they need to include stdlib.h themselves. (Also, since Python.h sets things like _POSIX_C_SOURCE and _XOPEN_SOURCE, including them in the wrong order can produce even more confusing errors, or errors that only appear on some platforms.)

I reopen the issue.

New changeset 52af0756b2ffc6788e364971d05cdaf127d77d5a by Victor Stinner in branch 'main':
bpo-45434: Only exclude <stdlib.h> in Python 3.11 limited C API (GH-29027)
https://github.com/python/cpython/commit/52af0756b2ffc6788e364971d05cdaf127d77d5a