Use correct `__reduce__` value for `test.test_copy.TestCopy.test_reduce_5tuple`

[Bobronium]

Feature or enhancement

Currently test_reduce_5tuple verifies that Lib/copy.py supports behavior which deviates from standard reduce protocol.

Here you can see that __reduce__ returns tuple with fifth element that is not an iterator:

cpython/Lib/test/test_copy.py

Lines 672 to 687 in 598d4c6

	def test_reduce_5tuple(self):
	class C(dict):
	def __reduce__(self):
	return (C, (), self.__dict__, None, self.items())
	def __eq__(self, other):
	return (dict(self) == dict(other) and
	self.__dict__ == other.__dict__)
	x = C([("foo", [1, 2]), ("bar", 3)])
	y = copy.copy(x)
	self.assertEqual(x, y)
	self.assertIsNot(x, y)
	self.assertIs(x["foo"], y["foo"])
	y = copy.deepcopy(x)
	self.assertEqual(x, y)
	self.assertIsNot(x, y)
	self.assertIsNot(x["foo"], y["foo"])

Pickle explicitly doesn't support that:

import pickle


class C(dict):
    def __reduce__(self):
        return (C, (), self.__dict__, None, self.items())

    def __eq__(self, other):
        return dict(self) == dict(other) and self.__dict__ == other.__dict__


x = C([("foo", [1, 2]), ("bar", 3)])

pickle.dumps(x)  # _pickle.PicklingError: fifth item of the tuple returned by __reduce__ must be an iterator, not dict_items

And when mentioning 4th and 5th elements, docs explicitly say:

Optionally, an iterator (and not a sequence)
Optionally, an iterator (not a sequence)

test_reduce_4tuple already correctly returns iterator:

cpython/Lib/test/test_copy.py

Lines 655 to 658 in 598d4c6

	def test_reduce_4tuple(self):
	class C(list):
	def __reduce__(self):
	return (C, (), self.__dict__, iter(self))

Proposal

I propose changing self.items() to iter(self.items()) so that this test only verifies that Lib/copy.py supports pickle protocol as it is documented.

No changes to Lib/copy.py are proposed, current behavior may be classified as an implementation detail.

Motivation

This will allow alternative implementations to rely on strict protocol compliance without breaking Lib/test/test_copy.py.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Linked PRs

• gh-141757: comply with pickle protocol in test_reduce_5tuple #141759
• [3.14] gh-141757: Comply with pickle protocol in test_reduce_5tuple (GH-141759) #141782
• [3.13] gh-141757: Comply with pickle protocol in test_reduce_5tuple (GH-141759) #141783

[serhiy-storchaka]

Thank you for your contribution @Bobronium.