PyInterpreterState_Main() is a function in the public C-API that returns a pointer to the main interpreter's state.  The main interpreter is the first one created by the CPython runtime during startup (e.g. when the "python" command is run).

Documentation for PyInterpreterState_Main() should be on the "Initialization, Finalization, and Threads" page of the C-API docs, probably in the "Sub-interpreter support" section. [1]  It could also possibly go in the "Advanced Debugger Support" section. [2]

FYI, I added PyInterpreterState_Main() at PyCon US 2017 (commit f5df46d701d29baf738365da6fcf1b8a3ceabb71) when I merged Nick Coghlan's internal implementation of PEP 432.  So it has been available since 3.7.


[1] https://docs.python.org/3/c-api/init.html#sub-interpreter-support
[2] https://docs.python.org/3/c-api/init.html#advanced-debugger-support

@Mariatta do you want to keep this for the mentored sprint at PyCon?

Since there was no response, I decided to  open a PR for this.

As I noted on the PR, this might be a good chance to make sure the C-API docs are clear about what the "main" interpreter is.

I will work on this in a separate PR.

I opened #issue36487 (https://bugs.python.org/issue36487) to track this.

New changeset 8c61739defd88c7f79e86537886c33745843ce01 by Miss Islington (bot) (Joannah Nanjekye) in branch 'master':
bpo-36157:Document PyInterpreterState_Main() (GH-12238)
https://github.com/python/cpython/commit/8c61739defd88c7f79e86537886c33745843ce01

New changeset 35fc38e5e82d18ceec95af9af2103319497e2eaf by Miss Islington (bot) in branch '3.7':
bpo-36157:Document PyInterpreterState_Main() (GH-12238)
https://github.com/python/cpython/commit/35fc38e5e82d18ceec95af9af2103319497e2eaf

Thanks for working on this, Joannah!  :)