`types.GeneratorType.gi_yieldfrom` is not correct

[bzoracler]

typeshed/stdlib/types.pyi

Lines 390 to 391 in d3cfe67

	@property
	def gi_yieldfrom(self) -> GeneratorType[_YieldT_co, _SendT_contra, Any] | None: ...

It's relatively simple to demonstrate counterexamples that are not GeneratorType objects. For example,

Iterator:

from collections.abc import Generator
from types import GeneratorType

def gf() -> Generator[int]:
    yield from [1, 2, 3, 4]

gen = gf()
assert type(gen) is GeneratorType
next(gen)  # 1
print(type(gen.gi_yieldfrom))  # <class 'list_iterator'>

builtins.coroutine_wrapper (some kind of collections.abc.Generator?):

# python 3.10
import asyncio

async def a():
    await asyncio.sleep(4)
    return 1

def gf():
    yield from a().__await__()

gen = gf()
next(gen)  # _asyncio.Future object
print(type(gen.gi_yieldfrom))  # <class 'coroutine_wrapper'>

---

So, what would be a useful type annotation for this that is still accurate? Would Iterator[Any] | None be OK, or do we have to do the same thing as types.CoroutineType.cr_await and erase all useful information for the type?

typeshed/stdlib/types.pyi

Lines 438 to 442 in d3cfe67

	class CoroutineType(Coroutine[_YieldT_co, _SendT_contra, _ReturnT_co]):
	__name__: str
	__qualname__: str
	@property
	def cr_await(self) -> Any | None: ...

[srittau]

Iterator sounds correct to me, although it should probably be Iterator[_YieldT_co].

Side note: The documentation of gi_yieldfrom seems incorrect to me:

object being iterated by yield from, or None

It's not the object being iterated, but the iterator of that iterable object.