[C API] Deprecate private functions which have a public replacement

[vstinner]

Hi,

Python 3.13 and 3.14 added public functions to replace private functions. For example, a public function PyBytes_Join() was added to replace the private function _PyBytes_Join().

I propose to deprecate the private functions which have a public replacement, and remove them in Python 3.16.

Victor

Linked PRs

• gh-128863: Deprecate private C API functions #128864
• gh-128863: Deprecate _PyLong_Sign() function #129176
• gh-128863: deprecate _PyLong_New() function #129212
• gh-128863: deprecate _PyLong_FromDigits() function #127939
• gh-128863: Deprecate the private _PyUnicodeWriter API #129245

[vstinner]

Previous discussion: https://discuss.python.org/t/remove-again-private-apis-which-now-have-new-public-replacement/68081

[vstinner]

Other deprecations to consider:

• _PyCode_GetExtra(): PyUnstable_Code_GetExtra()
• _PyCode_SetExtra(): PyUnstable_Code_SetExtra()
• _PyEval_RequestCodeExtraIndex(): PyUnstable_Eval_RequestCodeExtraIndex()
• _PyLong_AsByteArray(): PyLong_AsNativeBytes()
• _PyLong_FromByteArray(): PyLong_FromNativeBytes()
• _PyLong_FromDigits(): PyLongWriter_Create()
• _PyLong_New(): PyLongWriter_Create()
• _PyLong_Sign(): PyLong_GetSign()
• _PyUnicodeWriter_Init(): PyUnicodeWriter_Create() (and other _PyUnicodeWriter functions)

[skirpichev]

I'm closing #127937 and #127936 in favor of this issue.