Working on this at EuroPython2025:

Pythondocumentation on extending states the following:

All user-visible symbols defined by Python.h have a prefix of Py or PY, except those defined in standard header files. For convenience, and since they are used extensively by the Python interpreter, "Python.h" includes a few standard header files: <stdio.h>, <string.h>, <errno.h>, and <stdlib.h>. If the latter header file does not exist on your system, it declares the functions malloc(), free() and realloc() directly.

But this does not align with the current state ofPython.h. <errno.h>, <stdio.h>, <stdlib.h> and <string.h> headers are no longer used by Python. They are not included by limited C API version 3.11 and newer.

The <ctype.h> and <unistd.h> headers are also not included by limited C API version 3.13 and newer.

Linked PRs

• gh-136823: Update documentation on excluded headers in Python.h #136824