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 :-(