PEP 587 "Python Initialization Configuration" added a "Multi-Phase Initialization Private Provisional API":

• PyConfig._init_main
• _Py_InitializeMain()

The plan was to make the "core phase" more usable. But since Python 3.8, Python doesn't use this "Multi-Phase Initialization" API and I failed to find any user in 3rd party code.

I propose to remove this API in Python 3.14 without any deprecation since the feature was provisional and it's a private API.

Provisional:

A provisional API is one which has been deliberately excluded from the standard library’s backwards compatibility guarantees.

Linked PRs

• gh-129033: Remove _Py_InitializeMain() function #129034
• gh-129033: Remove _PyInterpreterState_SetConfig() function #129048
• gh-129033: Remove dead code in test.support.has_no_debug_ranges() #137379
• [3.14] gh-129033: Remove dead code in test.support.has_no_debug_ranges() (GH-137379) #137382