gh-116946: add Py_TPFLAGS_IMMUTABLETYPE to _random.Random

[picnixz]

On main the following leaks:

$ ./python -X showrefcount -c 'import _random; s = _random.Random(); t = type(s); t._random = s'[42 refs, 26 blocks]

• Issue: Heap types implemented in C must have Py_TPFLAGS_HAVE_GC and implement tp_traverse #116946

[ZeroIntensity]

LGTM with one idea.

[serhiy-storchaka]

Wait, why is _random.Random mutable?

[ZeroIntensity]

Probably because it would break code to change that.

[serhiy-storchaka]

It became mutable in 3.9. I think this is a bug.

[picnixz]

It became mutable in 3.9. I think this is a bug.

I was also surprised but I just didn't want to break stuff here.

[kumaraditya303]

It became mutable in 3.9. I think this is a bug.

Yes, I think adding IMMUTABLE flag was missed while conversion, it shouldn't be a mutable type.

[kumaraditya303]

See #88074 where most of the converted types where made immutable, same should be done for random and epoll

Stale

[picnixz]

@rhettinger Does this change satisfy you? do you want this to be backported?

[vstinner]

LGTM

[vstinner]

do you want this to be backported?

Please don't backport this change. It would be surprising that a class becomes immutable in 3.x.y bugfix release.

[serhiy-storchaka]

LGTM, but I would prefer a single large PR that fixes the 3.9 error by making all converted types immutable.