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.

This PR aligns the documentation with the code and the comments provided by the original author that implemented the changes.

Issue:Outdated documentation for including <errno.h>, <stdio.h>, <stdlib.h> and <string.h> in Python.h #136823

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Update documentation on excluded headers in Python.h

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Outdated documentation for including <errno.h>, <stdio.h>, <stdlib.h> and <string.h> in Python.h#136823

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SZeltaat commentedJul 19, 2025

Hi@AA-Turner, could you please take a look at this PR?
#EuroPython2025

StanFromIreland reviewed

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		``PY``, except those defined in standard header files.

		Note that:file:`Python.h` excludes ``<stdio.h>``, ``<string.h>``, ``<errno.h>``, and ``<stdlib.h>`` as they are not used by
		Python anymore. For backward compatibility of existing third party C extensions, they will

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Should we write down since which version they are no longer used, as we did for<ctype.h> and<unistd.h>?

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Seems like the right thing to do, but I couldn't find since which version they are no longer used.@vstinner, you seem to have added that comment to the code 4 years ago. Do you happen to know since which version?

AA-Turner added sprint needs backport to 3.13

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Comment on lines 80 to 83

		Note that:file:`Python.h` excludes ``<stdio.h>``, ``<string.h>``, ``<errno.h>``, and ``<stdlib.h>`` as they are not used by
		Python anymore. For backward compatibility of existing third party C extensions, they will
		be included if Py_LIMITED_API is not defined and for limited C API version 3.10 and older.
		The ``<ctype.h>`` and ``<unistd.h>`` headers are also not included for limited C API version 3.13 and newer.

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	Note that:file:`Python.h` excludes ``<stdio.h>``, ``<string.h>``, ``<errno.h>``, and ``<stdlib.h>`` as they are not used by
	Python anymore. For backward compatibility of existing third party C extensions, they will
	be included ifPy_LIMITED_API is not definedand for limited C API version 3.10 and older.
	The ``<ctype.h>`` and ``<unistd.h>`` headers are also not included for limited C API version 3.13 and newer.
	For backward compatibility of existing third party C extensions,:file:`Python.h`
	includes ``<stdio.h>``, ``<string.h>``, ``<errno.h>``, and ``<stdlib.h>`` iff
	:c:macro:`Py_LIMITED_API` is not definedor for limited C API version 3.10 and older.
	The ``<ctype.h>`` and ``<unistd.h>`` headers are also not included for limited C API version 3.13 and newer.