bpo-43973: Use Py_TPFLAGS_IMMUTABLETYPE to check for class assignments by erlend-aasland · Pull Request #25714 · python/cpython

cc. @vstinner

See msg392291: Can we get rid of the huge comment preceding the if statement now? Or at least reduce it considerably.

AFAICS, this does not require a news item, but I might be wrong.

Doesn't this also require a change?

Suggested :-

 if (compatible_for_assignment(oldto, newto, "__class__")) { 
     if (!(newto->tp_flags & Py_TPFLAGS_IMMUTABLETYPE)) { 
         Py_INCREF(newto); 
     } 
     Py_SET_TYPE(self, newto); 
     if (!(oldto->tp_flags & Py_TPFLAGS_IMMUTABLETYPE))
         Py_DECREF(oldto); 
     return 0; 
 } 
 else { 
     return -1; 
 } 

Doesn't this also require a change?

AFAICT, no. They adjust the ref. count if heap types are used:

If the old class was a heap type, decrement its ref. count. If the new class is a heap type, acquire a strong reference to it (increment the ref. count).

Merged, thanks for the fix.

The comment above the check should have been fixed to reflect the new semantics, no?

Also, is the explicit check for PyModule_Type still needed?

The comment above the check should have been fixed to reflect the new semantics, no?

Yes, and I believe it can be considerably reduced.

Also, is the explicit check for PyModule_Type still needed?

I don't know. See bpo-24912.