Isolate the itertools extension module

[erlend-aasland]

Feature or enhancement

Following https://github.com/ericsnowcurrently/multi-core-python/wiki/0-The-Plan we need to convert the itertools extension module to use module state.

There are multiple static global type objects:

cpython/Tools/c-analyzer/cpython/globals-to-fix.tsv

Lines 338 to 359 in e244401

	Modules/itertoolsmodule.c - _grouper_type -
	Modules/itertoolsmodule.c - accumulate_type -
	Modules/itertoolsmodule.c - batched_type -
	Modules/itertoolsmodule.c - chain_type -
	Modules/itertoolsmodule.c - combinations_type -
	Modules/itertoolsmodule.c - compress_type -
	Modules/itertoolsmodule.c - count_type -
	Modules/itertoolsmodule.c - cwr_type -
	Modules/itertoolsmodule.c - cycle_type -
	Modules/itertoolsmodule.c - dropwhile_type -
	Modules/itertoolsmodule.c - filterfalse_type -
	Modules/itertoolsmodule.c - groupby_type -
	Modules/itertoolsmodule.c - islice_type -
	Modules/itertoolsmodule.c - pairwise_type -
	Modules/itertoolsmodule.c - permutations_type -
	Modules/itertoolsmodule.c - product_type -
	Modules/itertoolsmodule.c - repeat_type -
	Modules/itertoolsmodule.c - starmap_type -
	Modules/itertoolsmodule.c - takewhile_type -
	Modules/itertoolsmodule.c - tee_type -
	Modules/itertoolsmodule.c - teedataobject_type -
	Modules/itertoolsmodule.c - ziplongest_type -

We need to convert these to heap types, add module state, and implement multi-phase init.

See also PEP-687.

I've got an old PR (#24065) that I'm planning on resurrecting. I'll re-submit it as multiple PRs; this is going to be a large change.

For this particular module, it could make sense to add a module state pointer to each type context, for easy and cheap state access.

Linked PRs

• gh-101277: Isolate itertools, add group and _grouper types to module state #101302
• gh-101277: Isolate itertools, part 2/4 #101303
• gh-101277: Isolate itertools, part 3/4 #101304
• gh-101277: Finalise isolating itertools #101305

[sobolevn]

cc @rhettinger as the module owner.