gh-149534: Fix unification of defaultdict and frozendict with |

[sobolevn]

I have a lot of free time today 😆

• defaultdict | frozendict returns dict, not defaultdict #149534

[sobolevn]

@JelleZijlstra you were right, there's a big behavior difference here.

>>>fromcollectionsimportOrderedDict>>>dict() |OrderedDict()
OrderedDict()
>>>frozendict() |OrderedDict()
frozendict()

Since OrderedDict and defaultdict are direct subtypes of dict, _PyDict_Or is never called for the first case.

cpython/Objects/typeobject.c

Lines 10531 to 10539 in 354ef33

	#defineSLOT1BINFULL(FUNCNAME, TESTFUNC, SLOTNAME, DUNDER, RDUNDER) \
	static PyObject * \
	FUNCNAME(PyObject *self, PyObject *other) \
	{ \
	PyObject* stack[2]; \
	PyThreadState *tstate = _PyThreadState_GET(); \
	int do_other = !Py_IS_TYPE(self, Py_TYPE(other)) && \
	Py_TYPE(other)->tp_as_number != NULL && \
	Py_TYPE(other)->tp_as_number->SLOTNAME == TESTFUNC; \

While it is called for frozendict.

I am not sure that this is a bug, though. It works as expected,, if you know all the little details. But, it might be unexpected for people who just want to swap dict to frozendict. The end result might be different.

@vstinner, what do you think?

[JelleZijlstra]

I don't have a strong opinion on what the right behavior is, but let's make sure that OrderedDict and defaultdict behave consistently at least.

[sobolevn]

@JelleZijlstra they do :)

>>>fromcollectionsimportOrderedDict, defaultdict>>>frozendict() |OrderedDict()
frozendict()
>>>frozendict() |defaultdict()
frozendict()

[vstinner]

@serhiy-storchaka wrote a similar fix for collections.OrderedDict: commit 7278904.

[sobolevn]

Thanks for the feedback. Done! Please, re-review my changes :)

[vstinner]

LGTM

[miss-islington-app]

Thanks @sobolevn for the PR 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-150709 is a backport of this pull request to the 3.15 branch.

[serhiy-storchaka]

And, like with OrderedDict, dict | defaultdict -> defaultdict, but frozendict | defaultdict -> frozendict.